US20030080370A1 - Multi-state non-volatile integrated circuit memory systems that employ dielectric storage elements - Google Patents
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- G11C16/0466—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells with charge storage in an insulating layer, e.g. metal-nitride-oxide-silicon [MNOS], silicon-oxide-nitride-oxide-silicon [SONOS]
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- G11C16/0483—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells having several storage transistors connected in series
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- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/41—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions
- H01L29/423—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions not carrying the current to be rectified, amplified or switched
- H01L29/42312—Gate electrodes for field effect devices
- H01L29/42316—Gate electrodes for field effect devices for field-effect transistors
- H01L29/4232—Gate electrodes for field effect devices for field-effect transistors with insulated gate
- H01L29/4234—Gate electrodes for transistors with charge trapping gate insulator
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/76—Unipolar devices, e.g. field effect transistors
- H01L29/772—Field effect transistors
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- H01L29/7923—Programmable transistors with more than two possible different levels of programmation
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- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B41/00—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates
- H10B41/30—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates characterised by the memory core region
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B41/00—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates
- H10B41/30—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates characterised by the memory core region
- H10B41/35—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates characterised by the memory core region with a cell select transistor, e.g. NAND
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B43/00—EEPROM devices comprising charge-trapping gate insulators
- H10B43/30—EEPROM devices comprising charge-trapping gate insulators characterised by the memory core region
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B69/00—Erasable-and-programmable ROM [EPROM] devices not provided for in groups H10B41/00 - H10B63/00, e.g. ultraviolet erasable-and-programmable ROM [UVEPROM] devices
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- G11C16/0466—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells with charge storage in an insulating layer, e.g. metal-nitride-oxide-silicon [MNOS], silicon-oxide-nitride-oxide-silicon [SONOS]
- G11C16/0475—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells with charge storage in an insulating layer, e.g. metal-nitride-oxide-silicon [MNOS], silicon-oxide-nitride-oxide-silicon [SONOS] comprising two or more independent storage sites which store independent data
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- G11C2216/02—Structural aspects of erasable programmable read-only memories
- G11C2216/06—Floating gate cells in which the floating gate consists of multiple isolated silicon islands, e.g. nanocrystals
Definitions
- This invention relates most specifically to non-volatile flash EEPROM (Electrically Erasable and Programmable Read Only Memory) cell arrays of a type using dielectric material charge storage elements.
- non-volatile flash EEPROM Electrically Erasable and Programmable Read Only Memory
- non-volatile memory products there are many commercially successful non-volatile memory products being used today, particularly in the form of small cards, where the memory cells have conductive floating gates, commonly of doped polysilicon material, on which an electron charge is stored to a level of the data state being stored.
- a common form of such memory cells has a “split-channel” between source and drain diffusions.
- the floating gate of the cell is positioned over one portion of the channel and the word line (also referred to as a control gate) is positioned over the other channel portion as well as the floating gate.
- a modification of this split-channel flash EEPROM cell adds a steering gate positioned between the floating gate and the word line.
- Each steering gate of an array extends over one column of floating gates, perpendicular to the word line. The effect is relieve the word line from having to perform two functions at the same time when reading or programming a selected cell. Those two functions are (1) to serve as a gate of a select transistor, thus requiring a proper voltage to turn the select transistor on and off, and (2) to drive the voltage of the floating gate to a desired level through an electric field (capacitive) coupling between the word line and the floating gate. It is often difficult to perform both of these functions in an optimum manner with a single voltage.
- the word line need only perform function (1), while the added steering gate performs function (2). Further, such cells may operate with source side programming, having an advantage of lower programming currents and/or voltages.
- steering gates in a flash EEPROM array is described in U.S. Pat. Nos. 5,313,421, 5,712,180, and 6,222,762, which patents are incorporated herein by this reference.
- Source side injection controls the substrate surface electrical potential along the length of the memory cell channel in a manner to create conditions for electron injection in a region of the channel away from the drain.
- Source side injection is also described in an article by Kamiya et al., “EPROM Cell with High Gate Injection Efficiency,” IEDM Technical Digest, 1982, pages 741-744, and in U.S. Pat. Nos. 4,622,656 and 5,313,421, which article and patents are incorporated herein by this reference.
- Two techniques for removing charge from floating gates to erase memory cells are used in both of the two types of memory cell arrays described above.
- One is to erase to the substrate by applying appropriate voltages to the source, drain, substrate and other gate(s) that cause electrons to tunnel through a portion of a dielectric layer between the floating gate and the substrate.
- the other erase technique transfers electrons from the floating gate to another gate through a tunnel dielectric layer positioned between them.
- a third gate is provided for that purpose.
- the floating gate is erased to the word line, without the necessity to add a fourth gate.
- Increased data density can also be achieved by reducing the physical size of the memory cells and/or of the overall array.
- Shrinking the size of integrated circuits is commonly performed for all types of circuits as processing techniques improve over time to permit implementing smaller feature sizes. But since there are limits of how far a given circuit layout can be shrunk by scaling through simple demagnification, efforts are so directed toward redesigning cells so that one or more features takes up less area.
- FIG. 1 An example is a dual floating gate memory cell connected in a NOR configuration, which can also be operated with the storage of multiple states on each floating gate.
- FIG. 1 A steering gate is included along each column of floating gates and a word line is provided thereover along each row of floating gates. When accessing a given floating gate for reading or programming, the steering gate over the other floating gate of the cell containing the floating gate of interest is raised sufficiently high to turn on the channel under the other floating gate no matter what charge level exists on it.
- Another type of memory cell useful in flash EEPROM systems utilizes a non-conductive dielectric material in place of a conductive floating gate to store charge in a non-volatile manner.
- a non-conductive dielectric material in place of a conductive floating gate to store charge in a non-volatile manner.
- Such a cell is described in an article by Chan et al., “A True Single-Transistor Oxide-Nitride-Oxide EEPROM Device,” IEEE Electron Device Letters , Vol. EDL-8, No. 3, March 1987, pp. 93-95.
- a triple layer dielectric formed of silicon oxide, silicon nitride and silicon oxide (“ONO”) is sandwiched between a conductive control gate and a surface of a semi-conductive substrate above the memory cell channel.
- the cell is programmed by injecting electrons from the cell channel into the nitride, where they are trapped and stored in a limited region. This stored charge then changes the threshold voltage of a portion of the channel of the cell in a manner that is detectable.
- the cell is erased by injecting hot holes into the nitride. See also Nozaki et al., “A 1-Mb EEPROM with MONOS Memory Cell for Semiconductor Disk Application,” IEEE Journal of Solid - State Circuits , Vol. 26, No. 4, April 1991, pp. 497-501, which describes a similar cell in a split-gate configuration where a doped polysilicon gate extends over a portion of the memory cell channel to form a separate select transistor.
- the programming techniques mentioned above, by reference to section 1.2 of the book edited by Brown and Brewer, are also described in that section to be applicable to dielectric charge-trapping devices.
- U.S. Pat. No. 5,851,881 incorporated herein by this reference, describes the use of two storage elements positioned adjacent each other over the channel of the memory cell, one being such a dielectric gate and the other a conductive floating gate. Two bits of data are stored, one in the dielectric and the other in the floating gate.
- the memory cell is programmed into one of four different threshold level combinations, representing one of four storage states, by programming each of the two gates into one of two different charge level ranges.
- the present invention includes two primary aspects that may either be implemented together or separately.
- One primary aspect is directed to novel non-volatile memory cell structures that use dielectric charge storage elements rather than conductive floating gates.
- the other primary aspect is directed to the storage of charge in one of more than two detectable levels at one or more limited, contained regions across a dielectric charge storage element over a channel of a memory cell transistor. More than one bit of data is thereby stored in a single localized region of the dielectric over a portion of the channel.
- Two or more such independently programmable charge storage regions, spaced apart from each other along the length of the channel may be provided in each memory cell of an array of such cells, wherein more than one bit of data is stored in each such region.
- This invention can be implemented in a number of prior flash memory systems, such as those described above in the Background.
- a prior memory cell array utilizes conductive floating gates as storage elements
- charge trapping dielectric material is substituted for the floating gates.
- the methods of making and operating such non-volatile memory systems with dielectric storage elements are quite similar to their conductive floating gate counterparts. Since charge does not move across a dielectric storage material, the dielectric may usually extend over most other areas of a memory cell array, across multiple rows and columns of memory cells. Where the memory cell includes a select transistor, however, gate dielectric is substituted within the select transistor for the electron storage material.
- Two or more electron storage elements can be provided within the storage dielectric of each memory cell that has a gate structure allowing independent control of the electric potential across the substrate surface in respective two or more portions along the length of the memory cell channel.
- only one charge storage region is maintained within each such storage element.
- the enlargement or movement of a region of the dielectric into which electrons are injected which can occur as the number of erase/programming cycles increases, thus does not affect an adjacent region within the same memory cell. This increases the number of erase/programming cycles that the memory can endure, thus increasing its effective life.
- This also makes it practical to store more than two memory states within each charge region since increased voltages, which are usually necessary to operate an enlarged window of charge that includes more than two charge levels defining multi-state storage, can also contribute to such enlargement or movement of the storage regions.
- the Dual Storage Element Cell described above in the Background has charge-storing dielectric substituted for each of the two floating gates of the memory cells.
- This dielectric is sandwiched between conductive steering gates and the substrate to form two functionally separate charge storage elements over channels of the memory cells between their sources and drains.
- One region of charge is stored in each of these two storage elements, which lie along the length of the cell channels on opposite sides of the select transistors.
- the level of charge in a region affects the threshold level of the portion of the length of the cell channel beneath that region. Two or more such charge levels, and thus two or more different threshold levels, are defined for programming into each of the two charge storage regions of each memory cell.
- Dual Storage Element Cell arrays in which the charge storage dielectric may be substituted for floating gates are given in U.S. Pat. Nos. 6,091,633, 6,103,573 and 6,151,248, and in pending applications Ser. No. 09/667,344, filed Sep.
- a NAND array has its memory cell floating gates replaced by storage element regions of a dielectric layer. This dielectric is sandwiched between word lines and the substrate surface. Otherwise, the array is operated as described in U.S. Pat. application Ser. No. 09/893,277, filed Jun. 27, 2001, which application is incorporated herein by this reference.
- Each storage element region may be operated to store more than two charge levels, thus storing more than one bit of data in each such region.
- FIG. 1 shows a plan view of a first example of an array of memory cells
- FIGS. 2A and 2B are cross-sectional views of the array of FIG. 1, taken at respective sections I-I and II-II;
- FIG. 3 is an enlarged view of the section of FIG. 2A, showing one memory cell, plus exemplary threshold voltage characteristics across that cell;
- FIG. 4 is a set of exemplary current-voltage characteristic curves for the memory cell of FIG. 3 operated in four states;
- FIG. 5 is an equivalent electrical circuit of the memory cell shown in FIG. 3, plus schematic representations of some operating elements;
- FIGS. 6A and 6B illustrate two different specific dielectric material configurations that may be used in memory cells for trapping charge
- FIG. 7 shows a plan view of a second example of an array of memory cells
- FIGS. 8A and 8B are cross-sectional views of the array of FIG. 7, taken at respective sections III-III and IV-IV;
- FIG. 9 is an enlarged view of the section of FIG. 8A, showing one memory cell, plus exemplary threshold voltage characteristics across that cell;
- FIG. 10 shows a plan view of a third example of an array of memory cells
- FIGS. 11A and 11B are cross-sectional views of the array of FIG. 10, taken at respective sections V-V and VI-VI;
- FIG. 12 is an enlarged view of the section of FIG. 11 A, showing one memory cell, plus exemplary threshold voltage characteristics across that cell;
- FIG. 13 is a section that shows a modification of the memory cells shown in FIG. 11A;
- FIG. 14 illustrates in block diagram form a flash EEPROM system in which the arrays of memory cells according to the first, second and third examples may be implemented;
- FIG. 15 is a plan view of a fourth example of memory cells
- FIGS. 16A and 16B are cross-sectional views of the array of FIG. 15, taken at respective sections VII-VII and VIII-VIII;
- FIG. 17 is an electrical equivalent circuit of a string of memory cells of the fourth example.
- FIGS. 18A, 18B and 18 C illustrate one process for forming a memory array of the type illustrated in FIGS. 15 - 17 ;
- FIG. 19 illustrates in block diagram form a flash EEPROM system in which the array of memory cells according to the fourth example may be implemented.
- FIG. 1 A few cells of a two-dimensional array of cells is illustrated in FIG. 1 in plan view, with orthogonal sections shown in FIGS. 2A and 2B.
- Elongated, parallel source and drain diffusions 103 , 104 and 105 are formed in a surface 101 of a semi-conductor substrate 100 , with their lengths extending in the y-direction and are spaced apart in the x-direction.
- a dielectric layer 107 including a charge storage material is formed on the substrate surface 101 .
- Elongated, parallel conductive control gates 109 , 110 and 111 have lengths extending in the x-direction and are spaced apart in the y-direction. These gates can be made from doped polysilicon material, as is typical.
- the charge storage elements of this simple structure are the areas of the dielectric layer 107 between the source and drain diffusions 103 - 105 and sandwiched between the control gates 109 - 111 and the substrate surface 101 . These storage element areas are marked with cross-hatching in FIG. 1.
- the charge trapping material needs to be positioned only in these regions in order to form operable memory cells but may be extended over any other portions of the structure that is convenient, including over the entire memory cell array.
- This memory cell array may be formed by standard processing techniques, particularly those developed for making flash EEPROM arrays of the type utilizing a floating gate.
- the major processing steps include forming an ion implant mask on the substrate surface through which ions are them implanted into the source and drain regions 103 - 105 . This mask is then removed and the dielectric layer 107 is formed over the entire array.
- control gates are doped in order to make them conductive by either initially depositing the polysilicon in a doped form or subsequently doping it by implanting ions before it is separated into the elongated strips 109 - 111 .
- the layer 107 in the regions being etched may also be removed, since those regions are unnecessary to the operation of the memory, to leave strips of the dielectric layer 107 under the control gates 109 - 111 .
- another implant may be made into the substrate between the control gate strips 109 - 111 , using the control gates as a mask, in order to increase the electrical isolation between adjacent rows of cells.
- FIG. 3 The programming and charge retention of such an array is illustrated in FIG. 3, where a portion of FIG. 2A including a single memory cell is enlarged. Programming is accomplished by the channel hot-electron injection technique described above in the Background. When appropriate voltages are placed on the substrate 100 , source 104 , drain 105 and control gate 110 , electrons are accelerated within the cell channel from the source toward the drain sufficiently to be injected into a region 115 within the dielectric layer 107 adjacent the drain 105 and retained there.
- the actual programming voltages applied depend upon details of the array structure but the following are exemplary: Substrate 100 : 0 volts; source 104 : 0 volts; drain 105 : 5 volts; and control gate 110 : 8 volts.
- the preferred programming technique follows that of flash EEPROMs with conductive floating gates, as described in references discussed above in the Background. Simultaneous pulses of these programming voltages are periodically applied to a number of cells in parallel and the programmed states of the cells are read in between programming pulses. When an individual cell reaches its programmed level, application of programming pulses to that cell is terminated. It will be noted that the source and drain diffusions are shared between cells in adjacent columns, and are operated in a virtual ground mode that is widely used in the operation of floating gate memory arrays.
- the length of the channel of the memory cell of FIG. 3 is noted to have two components, “L1” for the portion of the length outside of the charge storage region 115 , and “L2” for the portion of the length under the region 115 .
- a curve 117 illustrates the threshold voltage (V T ) characteristics of the channel. The curve is flat along the channel length segment L 1 at a level depending upon any threshold altering implant that may have been made in the substrate surface 101 and the impact of any prior channel erase operations (described hereinafter).
- the charge stored in the region 115 does not affect the threshold characteristics in the L 1 segment. But in the L 2 channel segment, the threshold is significantly affected by the stored charge, and, as in the floating gate counterpart systems, is the characteristic that is measured to determine the storage state of the cell.
- Each cell may be operated in binary, to store one bit of data, by detecting whether V T is above or below one predetermined threshold level. But according to one primary aspect of the present invention, more than one bit of data may be stored in each cell by operating it to distinguish between more than two levels or ranges of V T that are separated by more than two predetermined threshold levels.
- a window of threshold levels in the L 2 segment is shown in FIG. 3 to be divided into four states 0-3, as an example, which will store two bits per cell. More than four levels may alternatively be designated in order to store more than two bits per storage element.
- Exemplary current-voltage characteristics are shown in FIG. 4 for the cell of FIG. 3 in each of its four storage states as a result of an appropriate amount of charge being stored in the dielectric region 115 .
- the quantity V CG along the x-axis of FIG. 4 is the voltage on the control gate 110 of the cell
- the quantity I CELL on the y-axis is the current through the channel of the cell.
- the memory cell shown in FIG. 3 is effectively a split-channel cell because the charge storage region 115 extends across only a portion of the channel.
- An electrical equivalent circuit of the cell is shown in FIG. 5, two transistors Q 1 and Q 2 being connected in series between adjacent source and drain diffusions 104 and 105 (bit lines).
- the transistor Q 1 must be rendered conductive during programming or reading by providing a sufficient combination of voltages on the cell's elements.
- a voltage source 121 (V CG ) is connected to the control gate 110 (word line), a voltage source 125 (V S ) to the diffusion 104 and a voltage source 127 (V D ) to the diffusion 105 .
- the cell of FIG. 3 can be read in the same manner as a cell having a conductive floating gate.
- the control gate voltage V CG may be held fixed and the current through the cell (I CELL ) measured by a sense amplifier circuit 129 as an indication of the storage state of the cell.
- the actual voltages applied depend upon details of the array structure but the following are exemplary: Substrate 100 : 0 volts; source 104 : 0 volts; drain 105 : 1 volts; and control gate 110 : 3-5 volts.
- the control gate voltage V CG may be varied and its value noted when the value of the cell current is determined by the sense amplifier 129 to cross a fixed threshold.
- That voltage value gives an indication of the storage state of the cell.
- This example utilizes “forward” reading, since the drain during programming is also the drain during reading.
- the reading may be performed in a “reverse” mode, where the drain and source during programming are reversed during reading.
- the diagram of FIG. 5 also contains the components used to program the cell, except that the sense amplifier 129 is typically not connected during programming.
- the voltage sources 121 , 125 and 127 are connected as shown in FIG. 5 during programming but the values of the voltages supplied are different.
- a number of cells along at least one word line may be erased together by applying appropriate voltages to cause electrons to move from the dielectric charge trapping regions to the substrate.
- An example set of erase voltages is as follows: Substrate 100 : 0 volts; source 104 : floating; drain 105 : 5 volts; and control gate 110 : ⁇ 8 volts.
- FIG. 6 illustrates two exemplary structures for the charge storage dielectric layer 107 that may be used in all of the memory cell examples described herein.
- the first includes a layer 135 of silicon oxide (SiO 2 ), commonly just called “oxide,” grown on the substrate surface 101 , followed by a layer 137 of silicon nitride (Si 3 N 4 ), commonly just called “nitride,” being deposited over the layer 135 .
- a layer 139 of oxide is then grown on the nitride layer 137 or deposited on it, or a combination of the two. This oxide-nitride-oxide configuration is known as “ONO.” Electrons are trapped and stored in the nitride layer 137 .
- Exemplary thicknesses of these layers are as follows: layer 135 : 50 Angstroms; layer 137 : 70 Angstroms; and layer 139 : 100 Angstroms.
- the layer of conductive material from which the control gates are formed is then deposited on the ONO layer.
- the second structure uses a tailored layer 141 of silicon rich silicon dioxide to trap and store electrons.
- a tailored layer 141 of silicon rich silicon dioxide is described in the following two articles, which articles are incorporated herein in their entirety by this reference: DiMaria et al., “Electrically-alterable read-only-memory using Si-rich SIO 2 injectors and a floating polycrystalline silicon storage layer,” J. Appl. Phys. 52(7), July 1981, pp. 4825-4842; Hori et al., “A MOSFET with Si-implanted Gate-Si0 2 Insulator for Nonvolatile Memory Applications,” IEDM 92, April 1992, pp. 469-472.
- the thickness of the layer 141 can be about 500 Angstroms.
- FIGS. 7 - 9 Another example memory array is illustrated in FIGS. 7 - 9 , which differs from the first example by the use of two sets of orthogonally positioned conductive gates instead of just one set.
- FIG. 7 shows a few cells of the array in plan view and FIGS. 8A and 8B are cross-sectional views in two orthogonal directions.
- Parallel source and drain diffusions 151 , 152 and 153 formed in a surface 164 of a substrate 163 , are elongated in the y-direction across the array and spaced apart in the x-direction.
- Conductive control gates 155 , 156 and 157 which may be referred to as steering gates, are also elongated in the y-direction and spaced apart in the x-direction. These gates are positioned alongside respective diffusions 151 , 152 and 153 . These diffusions are spaced further apart than those of the first example in order to allow for these control gates to be positioned across the memory cell channels.
- a second set of conductive control gates 159 , 160 and 161 which form the word lines of the array, are elongated in the x-direction and spaced apart in the y-direction.
- the conductive gates are typically formed of doped polysilicon but may alternatively be formed of other low resistance materials.
- a layer of charge storing dielectric 165 is formed over the substrate surface 164 of the array.
- This dielectric can be one of the two specific dielectrics described above with respect to FIGS. 6 A-B.
- Another dielectric layer 167 is formed between the two sets of conductive gates where they cross each other. This layer is made to be relatively thick in order to sustain the potential voltage differences between the two sets of gates, such as a 250 Angstroms thick oxide.
- FIG. 8A and the enlarged sectional view of one memory cell thereof in FIG. 9, that the length of the individual memory cell channels is divided into two portions that are field coupled with different ones of the two sets of control gates.
- the word line 160 lies over the left approximately one-half of the channel length and the control gate 157 over the other.
- the charge storing dielectric 165 is sandwiched between the substrate surface 164 and these gates A primary difference in operation of this array from that of the first example is that charge may be stored in two spatially separated regions 171 and 173 within the layer 165 , and each of these regions may be individually programmed and read independently of the other.
- Programming by source side injection is preferred, which causes the charge storage region 171 to be located adjacent an interior edge of the gate 160 and the charge storage region 173 adjacent an interior edge of the gate 157 .
- electrons are stored in regions 172 and 174 within the layer 165 instead of in the regions 171 and 173 .
- the regions 172 and 174 are adjacent respective ones of the cell diffusions 152 and 153 .
- This example cell effectively contains two charge storage elements over its channel between adjacent source and drain regions 152 and 153 , one under the conductive gate 160 and the other under the conductive gate 157 .
- the dielectric layer 165 may be limited to these areas or, as is usually more convenient, extended over more of the array.
- FIGS. 7 - 9 show the charge storage layer 165 extending over the entire array.
- a curve 175 of FIG. 9 illustrates the varying threshold voltage characteristics (V T ) across the cell's channel, when programmed in the regions 171 and 173 by source side injection.
- the amount of charge stored in the region 171 imparts a V T value 177 of the threshold under it
- the amount of charge stored in the region 173 imparts a V T value 179 of the threshold under it.
- Each of the threshold values 177 and 179 may be maintained in one of two storage states, where a single breakpoint threshold value is set between the states. Two bits of data are stored in each cell if this is done.
- each of the values 177 and 179 may be operated with more than two levels, as shown in FIG. 3 for the first example array.
- each of the levels 177 and 179 is operated in four states, as shown in FIG. 3, a total of four bits of data are stored in each memory cell.
- a total of four bits of data are stored in each memory cell.
- the curve 175 is modified by the levels 177 and 179 being moved apart to positions under the charge storage regions 172 and 174 .
- Each of the threshold values 177 and 179 is preferably programmed and read independently of one another. One segment of the cell is turned on hard, thus eliminating any effect of its programmed threshold level, while the other is being programmed or read.
- the specific voltages applied to the array will depend upon its specific structure, the following are approximate voltages that might be used for programming the cell of FIG. 9 by channel hot-electron injection:
- Programming is also preferably accomplished in this example by alternately pulsing a plurality of cells with these voltages in parallel and verifying their programmed states by reading them, the programming being terminated on a cell-by-cell basis after reaching the desired level, as done with floating gate flash memory gate arrays.
- Exemplary reading voltages for the cell of FIG. 9, when programmed in the manner described above, are as follows:
- Erasing of the memory cells is accomplished in this and the other two examples by the injection of holes into their charge trapping layers. These holes neutralize the negative charge of the electrons that were injected into the charge-trapping layer during a programming operation. It is the layer 165 in this second example (FIGS. 7 - 9 ) that receives the electrons during programming and the holes during erasing. There are two specific erasing techniques. In one, the holes are injected into a charge storage portion of the layer 165 from the silicon substrate by tunneling through an oxide portion of that layer that is in contact with the substrate surface, termed a “channel erase.” To bring this about, a negative potential is applied to the word line with respect to the substrate, with the drain and source either being grounded or left floating.
- the holes are injected into the layer 165 from a region of the substrate near the drain or the source.
- a combination of a negative voltage on both the word lines 159 - 161 and steering gates 155 - 157 , and a positive voltage on the drains and sources 151 - 153 are applied.
- a positive voltage is applied to the drain 105
- the source 104 is left floating
- a negative voltage is applied to the word line 110 .
- the channel erase technique When cells have been programmed by source side injection, the channel erase technique is preferred. When programmed by the hot-electron injection technique, either of these two erasing techniques can be used. But when cells have been programmed by hot-electron injection, the channel erase has a disadvantage of tunneling holes across the entire channel, the result being an over erase of a portion of the charge trapping layer that does not contain electrons trapped by prior programming. This can cause the flat zero portions of the curve 175 (FIG. 9) across the cell channel to be lowered to negative threshold values.
- the memory cell array of FIGS. 7 - 9 may also be formed by standard processing techniques, particularly those developed for making flash EEPROM arrays of the type utilizing a floating gate.
- the layer 165 is first formed over the entire substrate area of the memory cell array. A first layer of polysilicon is then deposited over this area and etched through an appropriate mask to leave the control gates 155 - 157 . The layer 165 in between the control gates 155 - 157 is removed as part of this etching process, in one example.
- the source and drain regions 151 , 152 and 153 are then implanted through a mask formed by the control gates and other temporary masking material (not shown), thus being self-aligned with one edge of the control gates 155 - 157 .
- the layer 165 is then formed on the substrate surface 164 in between the control gates 155 - 157 and simultaneously over the top and sides of the control gates 155 - 157 .
- This is a continuous layer of ONO (FIG. 6A) or silicon rich oxide (FIG. 6B).
- the layer 167 shown in FIGS. 8 and 9 can be part of the same layer 165 or a combination of the layer 165 and other dielectric material.
- Such other dielectric material can be in the form of oxide spacers (not shown) formed along the vertical walls of the control gates 155 - 157 and/or a thick oxide layer (not shown) on the top surface of the control gates 155 - 157 .
- This top surface oxide is preferably formed by depositing the oxide on the top of the first polysilicon layer before it is separated into the gates 155 - 157 .
- a second layer of polysilicon is then formed over this continuous layer, and is then etched into the word lines 159 , 160 and 161 .
- this second example memory cell has a larger dimension in the x-direction by one resolution element than does the first example of FIGS. 1 - 3 , because of the added control (steering) gates 155 - 157 .
- a second polysilicon layer is also required in this second example. This added structure and size, however, allows the amount of data that is stored in each cell to be doubled.
- a useful modification of the cell of FIGS. 7 - 9 for some purposes replaces the electron storage layer under the control gates 155 - 157 with a thin (such as 200 Angstroms thick) gate dielectric, usually an oxide grown on the substrate surface 164 . This eliminates the second electron storage region 173 but adds an independent select transistor function to each cell. Erase can then be confined to individual rows of cells.
- an array of Dual Storage Element Cells is provided with its conductive floating gates replaced by portions of one of the dielectric charge trapping material layers described above with respect to FIGS. 6 A- 6 B.
- the making and operation of this array are similar to the arrays of Dual Storage Element Cells described in the patents and patent applications incorporated above into the Background and Summary.
- FIGS. 10 - 12 show an array.
- Source and drain diffusions 185 , 186 and 187 are formed in a surface 181 of a semi-conductive substrate 183 , and have their lengths extending in the y-direction and are spaced apart in the x-direction.
- conductive steering gates 189 , 190 , 191 , 192 , 193 and 194 are oriented in the same way as the diffusions, being positioned on either side of the diffusions in the x-direction.
- Conductive word lines 197 - 199 are oriented with lengths extending in the x-direction and are spaced apart in the y-direction. As typical, these conductive lines are made of doped polysilicon material.
- the steering gates 189 - 194 are positioned over a layer 201 of charge storage material according to one of FIGS. 6 A- 6 B. After the steering gates 189 - 194 are formed over the charge trapping layer 201 , strips of that layer extending in the y-direction are removed between every other of the steering gates in the x-direction. The source and drain regions 185 - 187 are implanted between the remaining regions between every other steering gate in the x-direction.
- An oxide layer 203 is formed over the tops and sides of the steering gates 189 - 194 to isolate those steering gates from the word lines 197 - 199 , and simultaneously formed over the exposed substrate surface 181 to provide gate oxide under the word lines 197 - 199 .
- An example thickness of the dielectric layer 203 is 200 Angstroms over the doped polysilicon steering gates 189 - 194 , and 150 Angstroms on the substrate surface 181 .
- the portions of the word line 198 shown in FIG. 11A, for example, that are formed immediately over the portion of the oxide layer 203 on the substrate surface 181 serve as the select transistor gates in that row of memory cells.
- Adjacent pairs of steering gates on either side of the diffusions 185 - 187 are preferably electrically connected together at a decoder for the steering gates in order to reduce the complexity of the decoder.
- One such pair includes steering gates 191 and 192 .
- Such adjacent pairs of steering gates may alternatively be physically merged together by joining them over their intermediate diffusions, as described in several of the Dual Storage Element Cell patents and applications referenced above.
- Individual storage elements can be defined to exist in regions of the dielectric trapping layer 201 under one of the steering gates 189 - 194 where one of the word lines 197 - 199 crosses, as shown in cross-hatching in the plan view of FIG. 10. There are two such storage elements per memory cell. Each storage element can be operated in two states (binary) in order to store 1 bit per storage element. The storage elements may alternatively be operated to individually store more than two states, such as four states per storage element, in a manner similar to that described in the Dual Storage Element Cell U.S. Pat. No. 6,151,248. The operation of such a dielectric storage memory array is similar to what is described in that patent, one difference being the use of lower voltages on the steering gates since there are no floating gates.
- FIG. 12 an enlarged view of one of the memory cells of FIG. 11A is given.
- Charge is trapped within the dielectric layer 201 in two regions 211 and 213 , adjacent to each side of a select transistor gate 198 ′ that is part of the word line 198 , if programmed by the source-side injection technique. If programmed by the channel hot-electron injection technique, on the other hand, these charge regions are located adjacent the source and drain regions 186 and 187 instead.
- the portions of the dielectric 201 within the memory cell on either side of the select transistor gate 198 ′ and beneath the word line 198 define the two storage elements of the cell that replace the two conductive floating gates of the Dual Storage Element Cell arrays and systems referenced above.
- the dielectric layer 201 can extend beyond these storage elements.
- the layer 201 is formed in strips having individual widths that extends in the x-direction between select transistors of memory cells in adjacent columns and lengths that extend in the y-direction across a large number of rows of memory cells. These strips, and the select transistor gate dielectric between them, can be self-aligned with edges of the steering gates, such as the edges of the steering gates 192 and 193 that are shown in FIG. 12.
- a curve portion 217 indicates a variation of the threshold voltage V T of a portion of the memory cell channel under the charge region 211 .
- the effect of the charge region 213 on the channel is indicated by the portion 219 of the curve 215 .
- Each of these regions may be operated in two states (storing one bit per cell) or more than two states (storing more than one bit per cell), as previously described above for the other examples. If programmed by channel hot-electron injection, on the other hand, the curve portions 217 and 219 are positioned further apart from each other, under the alternate locations of the charge trapped in the layer 201 that is mentioned above.
- FIG. 13 shows an optional modification of the memory cell shown in cross-section of FIGS. 11A and 12. The difference is that the select gate portion of the word line 198 ′ extends into a groove or recess 221 in the substrate 183 , with the select transistor gate dielectric 205 ′ formed between them along the bottom and walls of the groove 221 . This structure increases the length of the channel of the select transistor without taking any additional area across the substrate surface 181 .
- the gates in the foregoing structure are preferably made of doped polysilicon material, other suitable electrically conductive materials may be used in place of one or both of the polysilicon layers described.
- the second layer for example, from which the word lines 197 - 199 are formed, may be a polycide material, which is polysilicon with a conductive refractive metal silicide, such as tungsten, on its top surface in order to increase its conductivity.
- a polycide material is usually not preferred for the first conductive layer from which the steering gates 189 - 194 are formed because an oxide grown from a polycide as an interpoly dielectric is of lower quality than that grown from polysilicon.
- the second memory cell example described above For the first memory cell example, since only one layer of conductive gates is formed, those gates may be a polycide material.
- FIG. 14 An example memory system in which the various aspects of the present invention may be implemented is generally illustrated in the block diagram of FIG. 14. This system is most specifically directed to use of the second and third example arrays discussed above with control (steering) gates elongated in the y-direction but also has application to the first example by elimination of the circuits that connect to steering gates.
- a large number of individually addressable memory cells 11 are arranged in a regular array of rows and columns, although other physical arrangements of cells are certainly possible.
- Bit lines designated herein to extend along columns of the array 11 of cells, are electrically connected with a bit line decoder and driver circuit 13 through lines 15 .
- Word lines which are designated in this description to extend along rows of the array I 11 of cells, are electrically connected through lines 17 to a word line decoder and driver circuit 19 .
- Steering gates which extend along columns of memory cells in the array 11 , are electrically connected to a steering gate decoder and driver circuit 21 through lines 23 .
- the steering gates and/or bit lines may be connected to their respective decoders by techniques described in a co-pending patent application by Harari et al. entitled “Steering Gate and Bit Line Segmentation in Non-Volatile Memories,” U.S. Ser. No. 09/871,333, filed May 31, 2001, which application is incorporated herein by this reference.
- Each of the decoders 13 , 19 and 21 receives memory cell addresses over a bus 25 from a memory controller 27 .
- the decoder and driving circuits are also connected to the controller 27 over respective control and status signal lines 29 , 31 and 33 . Voltages applied to the steering gates and bit lines are coordinated through a bus 22 that interconnects the steering gates and bit line decoder and driver circuits 13 and 21 .
- the controller 27 is connectable through lines 35 to a host device (not shown).
- the host may be a personal computer, notebook computer, digital camera, audio player, various other hand held electronic devices, and the like.
- the memory system of FIG. 14 will commonly be implemented in a card according to one of several existing physical and electrical standards, such as one from the PCMCIA, the CompactFlashTM Association, the MMCTM Association, and others.
- the lines 35 terminate in a connector on the card that interfaces with a complementary connector of the host device.
- the electrical interface of many cards follows the ATA standard, wherein the memory system appears to the host as if it was a magnetic disk drive. Other memory card interface standards also exist.
- memory systems of the type shown in FIG. 14 are permanently embedded in the host device.
- the decoder and driver circuits 13 , 19 and 21 generate appropriate voltages in their respective lines of the array 11 , as addressed over the bus 25 , according to control signals in respective control and status lines 29 , 31 and 33 , to execute programming, reading and erasing functions. Any status signals, including voltage levels and other array parameters, are provided by the array 11 to the controller 27 over the same control and status lines 29 , 31 and 33 .
- a plurality of sense amplifiers within the circuit 13 receive current or voltage levels that are indicative of the states of addressed memory cells within the array 11 , and provides the controller 27 with information about those states over lines 41 during a read operation. A large number of such sense amplifiers are usually used in order to be able to read the states of a large number of memory cells in parallel.
- one row of cells is typically addressed at a time through the circuits 19 for accessing in the addressed row a number of cells that are selected by the circuits 13 and 21 .
- all cells in each of many rows are addressed together as a block for simultaneous erasure.
- a fourth example, illustrated in FIGS. 15 - 17 applies the dielectric storage techniques to a NAND array, the floating gate version of which is generally described in the Background above.
- Conductive word lines 241 - 244 elongated in the x-direction and spaced apart in the y-direction, extend across strips 245 - 249 of charge storage dielectric and intermediate isolation regions 251 - 254 formed of dielectric in trenches of the semi-conductor substrate 257 , as best seen in the cross-section of FIG. 16A.
- the dielectric strips 245 - 249 are elongated in the y-direction and spaced apart in the x-direction with one of the dielectric isolation strips 251 - 254 positioned therebetween.
- the dielectric strips 251 - 254 are preferably formed by typical silicon trench isolation (STI) techniques. Alternative techniques for providing electrical isolation between adjacent columns of memory cells may be used instead.
- STI silicon trench isolation
- the dielectric strips 245 - 249 are formed directly on the surface of the substrate 257 .
- the dielectric material and other characteristics are preferably those of one of the two described above with respect to FIGS. 6A and 6B.
- the word lines 241 - 244 are, in turn, positioned directly on top of these dielectric strips in regions that become charge storage regions.
- Charge storage regions 265 - 267 are indicated in FIG. 16A along the word line 242 , and regions 269 , 265 , 271 and 272 in FIG. 16B along the dielectric strip 246 .
- Doped source and drain regions are formed in surface areas of the substrate 257 between the word lines and the isolation dielectric.
- source and drain regions 261 - 263 are positioned in between word lines of a column formed between dielectric isolation strips 251 and 252 .
- This column forms one string of series connected memory cells, as shown in the cross-sectional view of FIG. 16B and represented by an electrical equivalent circuit diagram in FIG. 17.
- a switching select transistor shown in FIG. 16B at one end to have a gate 275 and at the other end to have a gate 277 .
- Terminals 279 and 281 form electrical ends of the string of storage and select transistors.
- One of these terminals is usually connected to an individual bit line and the other to a common potential.
- FIGS. 15 - 16 B illustrate the use of dielectric charge storage material in one specific NAND memory cell array structure. It will be recognized that dielectric charge storage material may also serve as charge storage elements in other specific NAND array structures.
- a group of memory cells one cell in each of several such column strings that is in a selected common row, are selected for simultaneous reading or programming.
- the row is selected by placing appropriate voltages on the word lines.
- the word lines of the rows within the associated NAND strings are raised to a relatively high voltage in order to render the memory cell transistors in those rows along each of the involved strings highly conductive, with the exception of the one row of cells that is desired to be read.
- the voltage of the word line of the selected row in the associated NAND strings is raised to a higher voltage compared with the word lines of the non-selected rows of the associated NAND strings.
- the select transistors at the ends of the strings of selected columns of cells are appropriately biased and appropriate voltages applied to their end terminals in order to carry out the desired reading or programming function.
- the same procedure can be applied to a NAND array of memory cells with dielectric storage media, such as that of FIGS. 15 - 17 .
- charge stored in the dielectric of a memory cell affects the threshold voltage of that cell.
- the level of charge stored in the region 265 of the dielectric strip 246 establishes the threshold voltage level of the memory cell transistor formed by that region, the adjacent source and drain regions 261 and 262 , a portion of the substrate between the source and drain that forms the cell's channel, and a portion of the word line 242 positioned over the channel.
- Each of the memory cell charge storage regions may be operated in two states or in more than two states, as previously described above for the other examples.
- One process for forming the NAND structure illustrated in FIGS. 15 - 16 B includes first forming a layer of the charge storage dielectric material such as ONO over the entire area of the substrate to be occupied by the array.
- a mask of silicon nitride material is formed on top of the ONO layer to define parallel, elongated trenches in the substrate used to isolate adjacent NAND strings.
- An etching step then removes the dielectric layer and forms trenches in the substrate through openings of the mask.
- Silicon oxide is then deposited over the structure to fill in the trenches and openings of the mask. Excess oxide is removed, followed by removal of the silicon nitride mask material. The result is the structure shown in FIGS. 16A and 16B without the word lines (WLs).
- the word lines are then formed by depositing a layer of doped polysilicon material over at least the array area and then etching away portions of the material through another mask in order to leave the word lines as shown in FIGS. 16A and 16B.
- An ion implant can then be made through the charge storage dielectric layer into regions of the substrate that remain exposed between the thick isolation dielectric and the word lines, thereby to form the source and drain regions.
- FIGS. 18A, 18B and 18 C Another process for forming a slightly different NAND dielectric storage array is illustrated by FIGS. 18A, 18B and 18 C. These views show the development of the structure along section VII-VII of the plan view of FIG. 15. Reference numbers of elements of FIGS. 18 A- 18 C that correspond to elements of FIGS. 15 - 16 B are the same with a double prime (′′) added.
- a layer of silicon nitride is deposited on the surface of the substrate 257 ′′, usually after growing a thin layer 296 of silicon dioxide on the substrate surface 257 ′′.
- a mask is then formed on the nitride layer with openings elongated in the y-direction (FIG. 15) and the nitride layer is etched away through the mask to leave nitride strips 291 - 295 that are elongated in the y-direction and spaced apart in the x-direction.
- the substrate is then etched in the spaces between the nitride strips that serve as a mask, thereby forming isolation trenches in the substrate.
- Those trenches are then filled with silicon oxide by depositing a thick oxide layer over the structure and then removing it to leave the portions 251 ′′, 252 ′′, 253 ′′and 254 ′′that fill the substrate trenches and extend slightly above the substrate surface.
- FIG. 18C A next series of steps is illustrated by FIG. 18C.
- the nitride strips 291 - 295 are removed by a selective etch that leaves the trench oxide between them and the substrate surface under them mostly unaffected.
- a layer 297 of charge storage dielectric, such as ONO, is then formed over the entire memory cell array area, covering the exposed substrate surface areas and the portions of the isolation dielectric extending above the substrate surface.
- Word lines are then formed by depositing a layer of doped polysilicon material over the entire area, forming a mask on top of the polysilicon layer with openings that are elongated in the x-direction and spaced apart in the y-direction, and then removing the polysilicon though the mask openings.
- Source and drain regions of the substrate can then be implanted through the charge storage dielectric layer 297 between the word lines and isolation oxide that serve as an implant mask.
- FIG. 18C has its charge storage dielectric layer 297 extending over the entire array area, while that of FIGS. 16A and 16B limits this dielectric layer to strips in between the thick isolation dielectric layers. In either case, a charge storage dielectric layer is provided over the channels of the NAND storage transistors where it is need to store charge.
- FIG. 19 Another example memory system in which the various aspects of the present invention may be implemented is illustrated by the block diagram of FIG. 19.
- Memory cell array 1 including a plurality of memory cells arranged in a matrix is controlled by a column control circuit 2 , a row control circuit 3 , a c-source control circuit 4 and a c-p-well control circuit 5 .
- This system is particularly suited to use a memory cell array 1 that is of the NAND type described above with respect to FIGS. 15 - 18 .
- a control circuit 2 is connected to bit lines (BL) of the memory cell array 1 for reading data stored in the memory cells, for establishing a state of the memory cells during a program operation, and for controlling potential levels of the bit lines (BL) to promote the programming or to inhibit the programming.
- BL bit lines
- each string of NAND memory cells described above can be connected to one of the bit lines, and the other terminal of the string to a common potential such as ground.
- the row control circuit 3 is connected to word lines (WL) to apply reading or programming voltages to the word lines. These voltages, combined with the bit line potential levels controlled by the column control circuit 2 , cause selected memory cells along one of the word lines to be read or programmed in parallel. An erase voltage is also applied by the circuits 2 to a p-type region on which the memory cells are formed.
- the c-source control circuit 4 controls a common source line (labeled as “c-source” in FIG. 18) connected to the memory cells.
- the c-p-well control circuit 5 controls the c-p-well voltage.
- the data stored in the memory cells are read out by the column control circuit 2 and are output to external I/O lines 51 via internal I/O lines 53 and a data input/output buffer 6 .
- Program data to be stored in the memory cells are input to the data input/output buffer 6 via the external I/O lines 51 , and transferred to the column control circuit 2 .
- the external I/O lines 51 are connected to a controller 43 .
- the controller includes various types of registers and other memory including a volatile random-access-memory (RAM) 45 .
- Command data for controlling the flash memory device are inputted to command circuits 7 through internal control lines 55 through external control lines 57 that are connected with the controller 43 .
- the command data informs the flash memory of what operation is requested.
- the input command is transferred to a state machine 8 that controls the column control circuit 2 , the row control circuit 3 , the c-source control circuit 4 , the c-p-well control circuit 5 and the data input/output buffer 6 .
- the state machine 8 can output a status data of the flash memory such as READY/BUSY or PASS/FAIL.
- the controller 43 is connected to, or connectable with, a host system such as a personal computer, a digital camera, or a personal digital assistant. It is the host that initiates commands, such as to store or read data to or from the memory array 1 , and provides or receives such data, respectively.
- the controller converts such commands into command signals that can be interpreted and executed by the command circuits 7 .
- the controller also typically contains buffer memory for the user data being written to or read from the memory array.
- a typical memory system includes one integrated circuit chip 47 that includes the controller 43 , and one or more integrated circuit chips 49 that each contain a memory array and associated control, input/output and state machine circuits. The trend, of course, is to integrate the memory array and controller circuits of a system together on one or more integrated circuit chips.
- Either of the memory systems of FIG. 14 or FIG. 19 may be embedded as part of the host system, or may be included in a memory card that is removably insertible into a mating socket of a host system. Such a card may include the entire memory system. Alternatively, the controller and memory array (with associated peripheral circuits) may be provided in separate cards. Several card implementations are described, for example, in U.S. Pat. No. 5,887,145, which patent is expressly incorporated herein in its entirety by this reference.
- FIG. 1 Other configurations of memory cell arrays that use conductive floating gates may similarly be modified to replace the floating gates with charge trapping dielectric material, and then to operate each charge storage region of the array either in binary (two states) or multi-states (more than two states).
- certain configurations described in patents and patent applications referenced above position either of the storage elements or source/drain diffusions in trenches, the trenches either being rectangular in cross-section or V-shaped.
- the conductive storage elements can also be replaced with charge trapping dielectric material.
Abstract
Description
- This is a continuation-in-part of application Ser. No. 10/002,696, filed Oct. 31, 2001, by the same inventors and entitled “Multi-State Non-Volatile Integrated Circuit Memory Systems that Employ Dielectric Storage Elements,” which application is incorporated herein in its entirety by this reference.
- This invention relates most specifically to non-volatile flash EEPROM (Electrically Erasable and Programmable Read Only Memory) cell arrays of a type using dielectric material charge storage elements.
- There are many commercially successful non-volatile memory products being used today, particularly in the form of small cards, where the memory cells have conductive floating gates, commonly of doped polysilicon material, on which an electron charge is stored to a level of the data state being stored. A common form of such memory cells has a “split-channel” between source and drain diffusions. The floating gate of the cell is positioned over one portion of the channel and the word line (also referred to as a control gate) is positioned over the other channel portion as well as the floating gate. This effectively forms a cell with two transistors in series, one (the memory transistor) with a combination of the amount of charge on the floating gate and the voltage on the word line controlling the amount of current that can flow through its portion of the channel, and the other (the select transistor) having the word line alone serving as its gate. The word line extends over a row of floating gates. Examples of such cells, their uses in memory systems and methods of manufacturing them are given in U.S. Pat. Nos. 5,070,032, 5,095,344, 5,315,541, 5,343,063, and 5,661,053, and in co-pending U.S. patent application Ser. No. 09/239,073, filed Jan. 27, 1999, which patents and application are incorporated herein by this reference.
- A modification of this split-channel flash EEPROM cell adds a steering gate positioned between the floating gate and the word line. Each steering gate of an array extends over one column of floating gates, perpendicular to the word line. The effect is relieve the word line from having to perform two functions at the same time when reading or programming a selected cell. Those two functions are (1) to serve as a gate of a select transistor, thus requiring a proper voltage to turn the select transistor on and off, and (2) to drive the voltage of the floating gate to a desired level through an electric field (capacitive) coupling between the word line and the floating gate. It is often difficult to perform both of these functions in an optimum manner with a single voltage. With the addition of the steering gate, the word line need only perform function (1), while the added steering gate performs function (2). Further, such cells may operate with source side programming, having an advantage of lower programming currents and/or voltages. The use of steering gates in a flash EEPROM array is described in U.S. Pat. Nos. 5,313,421, 5,712,180, and 6,222,762, which patents are incorporated herein by this reference.
- The foregoing incorporated references have their memory cells connected in what is generally referred to as a NOR configuration. The individual memory cells, which have one or two floating gate storage elements, are connected between adjacent bit lines to which adjacent cells in rows of cells are also connected. One bit line is connected to both source diffusions of one column of cells and drain diffusions of an immediately adjacent column of cells, in what is termed a virtual ground array. In another type of array architecture, generally referred to as a NAND configuration, eight, sixteen or more memory cells are connected in series with each other and select transistors in strings connected between individual bit lines and a common potential. Examples of such arrays and their operation are described in U.S. Pat. No. 6,046,935, which patent is expressly incorporated herein in its entirety by this reference.
- There are various programming techniques for injecting electrons from the substrate onto the floating gate through the gate dielectric. The most common programming mechanisms are described in a book edited by Brown and Brewer, “Nonvolatile Semiconductor Memory Technology,” IEEE Press, section 1.2, pages 9-25 (1998), which section is incorporated herein by this reference. One technique, termed “Fowler-Nordheim tunneling” (section 1.2.1), causes electrons to tunnel through the floating gate dielectric under the influence of a high field that is established thereacross by a voltage difference between the control gate and the substrate channel. Another technique, termed channel “hot-electron injection” (section 1.2.3), injects electrons from the cell's channel into a region of the floating gate adjacent the cell's drain. Yet another technique, termed “source side injection” (section 1.2.4), controls the substrate surface electrical potential along the length of the memory cell channel in a manner to create conditions for electron injection in a region of the channel away from the drain. Source side injection is also described in an article by Kamiya et al., “EPROM Cell with High Gate Injection Efficiency,”IEDM Technical Digest, 1982, pages 741-744, and in U.S. Pat. Nos. 4,622,656 and 5,313,421, which article and patents are incorporated herein by this reference.
- Two techniques for removing charge from floating gates to erase memory cells are used in both of the two types of memory cell arrays described above. One is to erase to the substrate by applying appropriate voltages to the source, drain, substrate and other gate(s) that cause electrons to tunnel through a portion of a dielectric layer between the floating gate and the substrate.
- The other erase technique transfers electrons from the floating gate to another gate through a tunnel dielectric layer positioned between them. In the first type of cell described above, a third gate is provided for that purpose. In the second type of cell described above, which already has three gates because of the use of a steering gate, the floating gate is erased to the word line, without the necessity to add a fourth gate. Although this later technique adds back a second function to be performed by the word line, these functions are performed at different times, thus avoiding the necessity of making compromises to accommodate the two functions.
- It is continuously desired to increase the amount of digital data that can be stored in a given area of a silicon substrate, in order to increase the storage capacity of a given size memory card and other types packages, or to both increase capacity and decrease size. One way to increase the storage density of data is to store more than one bit of data per memory cell. This is accomplished by dividing a window of a floating gate charge level voltage range into more than two states. The use of four such states allows each cell to store two bits of data, a cell with sixteen states stores four bits of data, and so on. A multiple state flash EEPROM structure and operation is described in U.S. Pat. Nos. 5,043,940 and 5,172,338, which patents are incorporated herein by this reference.
- Increased data density can also be achieved by reducing the physical size of the memory cells and/or of the overall array. Shrinking the size of integrated circuits is commonly performed for all types of circuits as processing techniques improve over time to permit implementing smaller feature sizes. But since there are limits of how far a given circuit layout can be shrunk by scaling through simple demagnification, efforts are so directed toward redesigning cells so that one or more features takes up less area.
- In addition, different designs of memory cells have been implemented in order to further increase data storage density. An example is a dual floating gate memory cell connected in a NOR configuration, which can also be operated with the storage of multiple states on each floating gate. In this type of cell, two floating gates are included over its channel between source and drain diffusions with a select transistor in between them. A steering gate is included along each column of floating gates and a word line is provided thereover along each row of floating gates. When accessing a given floating gate for reading or programming, the steering gate over the other floating gate of the cell containing the floating gate of interest is raised sufficiently high to turn on the channel under the other floating gate no matter what charge level exists on it. This effectively eliminates the other floating gate as a factor in reading or programming the floating gate of interest in the same memory cell. For example, the amount of current flowing through the cell, which can be used to read its state, is then a function of the amount of charge on the floating gate of interest but not of the other floating gate in the same cell. An example of this cell array architecture, its manufacture and operating techniques are described in U.S. Pat. No. 5,712,180 (FIGS.9+), which patent is incorporated herein by this reference (hereinafter referred to as the “Dual Storage Element Cell”).
- Another type of memory cell useful in flash EEPROM systems utilizes a non-conductive dielectric material in place of a conductive floating gate to store charge in a non-volatile manner. Such a cell is described in an article by Chan et al., “A True Single-Transistor Oxide-Nitride-Oxide EEPROM Device,”IEEE Electron Device Letters, Vol. EDL-8, No. 3, March 1987, pp. 93-95. A triple layer dielectric formed of silicon oxide, silicon nitride and silicon oxide (“ONO”) is sandwiched between a conductive control gate and a surface of a semi-conductive substrate above the memory cell channel. The cell is programmed by injecting electrons from the cell channel into the nitride, where they are trapped and stored in a limited region. This stored charge then changes the threshold voltage of a portion of the channel of the cell in a manner that is detectable. The cell is erased by injecting hot holes into the nitride. See also Nozaki et al., “A 1-Mb EEPROM with MONOS Memory Cell for Semiconductor Disk Application,” IEEE Journal of Solid-State Circuits, Vol. 26, No. 4, April 1991, pp. 497-501, which describes a similar cell in a split-gate configuration where a doped polysilicon gate extends over a portion of the memory cell channel to form a separate select transistor. The foregoing two articles are incorporated herein by this reference. The programming techniques mentioned above, by reference to section 1.2 of the book edited by Brown and Brewer, are also described in that section to be applicable to dielectric charge-trapping devices.
- U.S. Pat. No. 5,851,881, incorporated herein by this reference, describes the use of two storage elements positioned adjacent each other over the channel of the memory cell, one being such a dielectric gate and the other a conductive floating gate. Two bits of data are stored, one in the dielectric and the other in the floating gate. The memory cell is programmed into one of four different threshold level combinations, representing one of four storage states, by programming each of the two gates into one of two different charge level ranges.
- Another approach to storing two bits in each cell has been described by Eitan et al., “NROM: A Novel Localized Trapping, 2-Bit Nonvolatile Memory Cell,”IEEE Electron Device Letters, vol. 21, no. 11, November 2000, pp. 543-545. An ONO dielectric layer extends across the channel between source and drain diffusions. The charge for one data bit is localized in the dielectric layer adjacent to the drain, and the charge for the other data bit localized in the dielectric layer adjacent to the source. Multi-state data storage is obtained by separately reading binary states of the spatially separated charge storage regions within the dielectric.
- The present invention includes two primary aspects that may either be implemented together or separately. One primary aspect is directed to novel non-volatile memory cell structures that use dielectric charge storage elements rather than conductive floating gates. The other primary aspect is directed to the storage of charge in one of more than two detectable levels at one or more limited, contained regions across a dielectric charge storage element over a channel of a memory cell transistor. More than one bit of data is thereby stored in a single localized region of the dielectric over a portion of the channel. Two or more such independently programmable charge storage regions, spaced apart from each other along the length of the channel, may be provided in each memory cell of an array of such cells, wherein more than one bit of data is stored in each such region.
- This invention can be implemented in a number of prior flash memory systems, such as those described above in the Background. Where a prior memory cell array utilizes conductive floating gates as storage elements, charge trapping dielectric material is substituted for the floating gates. The methods of making and operating such non-volatile memory systems with dielectric storage elements are quite similar to their conductive floating gate counterparts. Since charge does not move across a dielectric storage material, the dielectric may usually extend over most other areas of a memory cell array, across multiple rows and columns of memory cells. Where the memory cell includes a select transistor, however, gate dielectric is substituted within the select transistor for the electron storage material.
- Two or more electron storage elements can be provided within the storage dielectric of each memory cell that has a gate structure allowing independent control of the electric potential across the substrate surface in respective two or more portions along the length of the memory cell channel. In the preferred implementations of the present invention, only one charge storage region is maintained within each such storage element. The enlargement or movement of a region of the dielectric into which electrons are injected, which can occur as the number of erase/programming cycles increases, thus does not affect an adjacent region within the same memory cell. This increases the number of erase/programming cycles that the memory can endure, thus increasing its effective life. This also makes it practical to store more than two memory states within each charge region since increased voltages, which are usually necessary to operate an enlarged window of charge that includes more than two charge levels defining multi-state storage, can also contribute to such enlargement or movement of the storage regions.
- In a particular example, the Dual Storage Element Cell described above in the Background has charge-storing dielectric substituted for each of the two floating gates of the memory cells. This dielectric is sandwiched between conductive steering gates and the substrate to form two functionally separate charge storage elements over channels of the memory cells between their sources and drains. One region of charge is stored in each of these two storage elements, which lie along the length of the cell channels on opposite sides of the select transistors. The level of charge in a region affects the threshold level of the portion of the length of the cell channel beneath that region. Two or more such charge levels, and thus two or more different threshold levels, are defined for programming into each of the two charge storage regions of each memory cell. Programming and reading of a selected one of the two charge storage regions of an addressed cell is accomplished in the same manner as in the dual floating gate systems, by turning on the select transistor and driving the other channel portion strongly conductive. This renders the selected charge storage region of the addressed cell responsive to voltages placed on its source, drain and gates. Specific examples of Dual Storage Element Cell arrays in which the charge storage dielectric may be substituted for floating gates are given in U.S. Pat. Nos. 6,091,633, 6,103,573 and 6,151,248, and in pending applications Ser. No. 09/667,344, filed Sep. 22, 2000, by Yuan et al., entitled “Non-volatile Memory Cell Array having Discontinuous Source and Drain Diffusions Contacted by Continuous Bit Line Conductors and Methods of Forming,” Ser. No. 09/925,134, filed Aug. 8, 2001, by Harari et al., entitled “Non-Volatile Memory Cells Utilizing Substrate Trenches,” and Ser. No. 09/925,102, filed Aug. 8, 2001, by Yuan et al., entitled “Scalable Self-Aligned Dual Floating Gate Memory Cell Array and Methods of Forming the Array,” which patents and patent applications are incorporated herein in their entirety by this reference.
- In another specific example, a NAND array has its memory cell floating gates replaced by storage element regions of a dielectric layer. This dielectric is sandwiched between word lines and the substrate surface. Otherwise, the array is operated as described in U.S. Pat. application Ser. No. 09/893,277, filed Jun. 27, 2001, which application is incorporated herein by this reference. Each storage element region may be operated to store more than two charge levels, thus storing more than one bit of data in each such region.
- Additional aspects, advantages and features of the present invention are included in the following description of its exemplary embodiments, which description should be read in conjunction with the accompanying drawings.
- FIG. 1 shows a plan view of a first example of an array of memory cells;
- FIGS. 2A and 2B are cross-sectional views of the array of FIG. 1, taken at respective sections I-I and II-II;
- FIG. 3 is an enlarged view of the section of FIG. 2A, showing one memory cell, plus exemplary threshold voltage characteristics across that cell;
- FIG. 4 is a set of exemplary current-voltage characteristic curves for the memory cell of FIG. 3 operated in four states;
- FIG. 5 is an equivalent electrical circuit of the memory cell shown in FIG. 3, plus schematic representations of some operating elements;
- FIGS. 6A and 6B illustrate two different specific dielectric material configurations that may be used in memory cells for trapping charge;
- FIG. 7 shows a plan view of a second example of an array of memory cells;
- FIGS. 8A and 8B are cross-sectional views of the array of FIG. 7, taken at respective sections III-III and IV-IV;
- FIG. 9 is an enlarged view of the section of FIG. 8A, showing one memory cell, plus exemplary threshold voltage characteristics across that cell;
- FIG. 10 shows a plan view of a third example of an array of memory cells;
- FIGS. 11A and 11B are cross-sectional views of the array of FIG. 10, taken at respective sections V-V and VI-VI;
- FIG. 12 is an enlarged view of the section of FIG. 11 A, showing one memory cell, plus exemplary threshold voltage characteristics across that cell;
- FIG. 13 is a section that shows a modification of the memory cells shown in FIG. 11A;
- FIG. 14 illustrates in block diagram form a flash EEPROM system in which the arrays of memory cells according to the first, second and third examples may be implemented;
- FIG. 15 is a plan view of a fourth example of memory cells;
- FIGS. 16A and 16B are cross-sectional views of the array of FIG. 15, taken at respective sections VII-VII and VIII-VIII;
- FIG. 17 is an electrical equivalent circuit of a string of memory cells of the fourth example;
- FIGS. 18A, 18B and18C illustrate one process for forming a memory array of the type illustrated in FIGS. 15-17; and
- FIG. 19 illustrates in block diagram form a flash EEPROM system in which the array of memory cells according to the fourth example may be implemented.
- Several specific memory cell configurations are described with respect to the drawings. In each of them, charge is stored in at least one region of a charge trapping dielectric that is positioned between a conductive gate and the substrate. These memory cell examples may be operated either in a binary mode, where one bit of data is stored in each charge region, or in a multi-state mode, where more than one bit of data is stored in each region.
- First Memory Cell Example (FIGS.1-6)
- A few cells of a two-dimensional array of cells is illustrated in FIG. 1 in plan view, with orthogonal sections shown in FIGS. 2A and 2B. Elongated, parallel source and drain
diffusions surface 101 of asemi-conductor substrate 100, with their lengths extending in the y-direction and are spaced apart in the x-direction. Adielectric layer 107 including a charge storage material is formed on thesubstrate surface 101. Elongated, parallelconductive control gates - The charge storage elements of this simple structure (which is one of its advantages) are the areas of the
dielectric layer 107 between the source and drain diffusions 103-105 and sandwiched between the control gates 109-111 and thesubstrate surface 101. These storage element areas are marked with cross-hatching in FIG. 1. The charge trapping material needs to be positioned only in these regions in order to form operable memory cells but may be extended over any other portions of the structure that is convenient, including over the entire memory cell array. - This memory cell array may be formed by standard processing techniques, particularly those developed for making flash EEPROM arrays of the type utilizing a floating gate. The major processing steps include forming an ion implant mask on the substrate surface through which ions are them implanted into the source and drain regions103-105. This mask is then removed and the
dielectric layer 107 is formed over the entire array. A layer of conductive material, such as doped polysilicon or polycide, is then deposited over the dielectric 107, an etch mask formed on its top surface and the polysilicon is then etched through the mask to leave the control gates 109-111. In the case of polysilicon, these control gates are doped in order to make them conductive by either initially depositing the polysilicon in a doped form or subsequently doping it by implanting ions before it is separated into the elongated strips 109-111. When the polysilicon is etched, thelayer 107 in the regions being etched may also be removed, since those regions are unnecessary to the operation of the memory, to leave strips of thedielectric layer 107 under the control gates 109-111. Finally, another implant may be made into the substrate between the control gate strips 109-111, using the control gates as a mask, in order to increase the electrical isolation between adjacent rows of cells. - The programming and charge retention of such an array is illustrated in FIG. 3, where a portion of FIG. 2A including a single memory cell is enlarged. Programming is accomplished by the channel hot-electron injection technique described above in the Background. When appropriate voltages are placed on the
substrate 100,source 104, drain 105 andcontrol gate 110, electrons are accelerated within the cell channel from the source toward the drain sufficiently to be injected into aregion 115 within thedielectric layer 107 adjacent thedrain 105 and retained there. The actual programming voltages applied depend upon details of the array structure but the following are exemplary: Substrate 100: 0 volts; source 104: 0 volts; drain 105: 5 volts; and control gate 110: 8 volts. - The preferred programming technique follows that of flash EEPROMs with conductive floating gates, as described in references discussed above in the Background. Simultaneous pulses of these programming voltages are periodically applied to a number of cells in parallel and the programmed states of the cells are read in between programming pulses. When an individual cell reaches its programmed level, application of programming pulses to that cell is terminated. It will be noted that the source and drain diffusions are shared between cells in adjacent columns, and are operated in a virtual ground mode that is widely used in the operation of floating gate memory arrays.
- The length of the channel of the memory cell of FIG. 3 is noted to have two components, “L1” for the portion of the length outside of the
charge storage region 115, and “L2” for the portion of the length under theregion 115. Acurve 117 illustrates the threshold voltage (VT) characteristics of the channel. The curve is flat along the channel length segment L1 at a level depending upon any threshold altering implant that may have been made in thesubstrate surface 101 and the impact of any prior channel erase operations (described hereinafter). The charge stored in theregion 115 does not affect the threshold characteristics in the L1 segment. But in the L2 channel segment, the threshold is significantly affected by the stored charge, and, as in the floating gate counterpart systems, is the characteristic that is measured to determine the storage state of the cell. - Programming by Fowler-Nordheim tunneling through the layer of oxide formed on the channel region has its limitations. It can usually be used in only some specific memory array configurations, such as NAND and AND configurations. It is not practical to program this first example, or either of the second or third memory cell array examples described hereinafter, by this technique. But if programmed in this manner, the storage region within the dielectric107 would extend substantially uniformly across the entire channel length (L1+L2) instead of being confined to the
region 115. - Each cell may be operated in binary, to store one bit of data, by detecting whether VT is above or below one predetermined threshold level. But according to one primary aspect of the present invention, more than one bit of data may be stored in each cell by operating it to distinguish between more than two levels or ranges of VT that are separated by more than two predetermined threshold levels. A window of threshold levels in the L2 segment is shown in FIG. 3 to be divided into four states 0-3, as an example, which will store two bits per cell. More than four levels may alternatively be designated in order to store more than two bits per storage element. Exemplary current-voltage characteristics are shown in FIG. 4 for the cell of FIG. 3 in each of its four storage states as a result of an appropriate amount of charge being stored in the
dielectric region 115. The quantity VCG along the x-axis of FIG. 4 is the voltage on thecontrol gate 110 of the cell, and the quantity ICELL on the y-axis is the current through the channel of the cell. - The memory cell shown in FIG. 3 is effectively a split-channel cell because the
charge storage region 115 extends across only a portion of the channel. An electrical equivalent circuit of the cell is shown in FIG. 5, two transistors Q1 and Q2 being connected in series between adjacent source and drain diffusions 104 and 105 (bit lines). The transistor Q1 must be rendered conductive during programming or reading by providing a sufficient combination of voltages on the cell's elements. During read, a voltage source 121 (VCG) is connected to the control gate 110 (word line), a voltage source 125 (VS) to thediffusion 104 and a voltage source 127 (VD) to thediffusion 105. - The cell of FIG. 3 can be read in the same manner as a cell having a conductive floating gate. There are two general ways. The control gate voltage VCG may be held fixed and the current through the cell (ICELL) measured by a
sense amplifier circuit 129 as an indication of the storage state of the cell. The actual voltages applied depend upon details of the array structure but the following are exemplary: Substrate 100: 0 volts; source 104: 0 volts; drain 105: 1 volts; and control gate 110: 3-5 volts. Alternatively, the control gate voltage VCG may be varied and its value noted when the value of the cell current is determined by thesense amplifier 129 to cross a fixed threshold. That voltage value gives an indication of the storage state of the cell. This example utilizes “forward” reading, since the drain during programming is also the drain during reading. Alternatively, the reading may be performed in a “reverse” mode, where the drain and source during programming are reversed during reading. - The diagram of FIG. 5 also contains the components used to program the cell, except that the
sense amplifier 129 is typically not connected during programming. Thevoltage sources - FIG. 6 illustrates two exemplary structures for the charge
storage dielectric layer 107 that may be used in all of the memory cell examples described herein. The first (FIG. 6A) includes alayer 135 of silicon oxide (SiO2), commonly just called “oxide,” grown on thesubstrate surface 101, followed by alayer 137 of silicon nitride (Si3N4), commonly just called “nitride,” being deposited over thelayer 135. Alayer 139 of oxide is then grown on thenitride layer 137 or deposited on it, or a combination of the two. This oxide-nitride-oxide configuration is known as “ONO.” Electrons are trapped and stored in thenitride layer 137. Exemplary thicknesses of these layers are as follows: layer 135: 50 Angstroms; layer 137: 70 Angstroms; and layer 139: 100 Angstroms. The layer of conductive material from which the control gates are formed is then deposited on the ONO layer. - The second structure, shown in FIG. 6B, uses a tailored
layer 141 of silicon rich silicon dioxide to trap and store electrons. Such material is described in the following two articles, which articles are incorporated herein in their entirety by this reference: DiMaria et al., “Electrically-alterable read-only-memory using Si-rich SIO2 injectors and a floating polycrystalline silicon storage layer,” J. Appl. Phys. 52(7), July 1981, pp. 4825-4842; Hori et al., “A MOSFET with Si-implanted Gate-Si02 Insulator for Nonvolatile Memory Applications,” IEDM 92, April 1992, pp. 469-472. As an example, the thickness of thelayer 141 can be about 500 Angstroms. - Second Memory Cell Example
- Another example memory array is illustrated in FIGS.7-9, which differs from the first example by the use of two sets of orthogonally positioned conductive gates instead of just one set. FIG. 7 shows a few cells of the array in plan view and FIGS. 8A and 8B are cross-sectional views in two orthogonal directions. Parallel source and drain
diffusions surface 164 of asubstrate 163, are elongated in the y-direction across the array and spaced apart in the x-direction.Conductive control gates respective diffusions conductive control gates - Referring to the sectional views of FIGS. 8A and 8B, a layer of
charge storing dielectric 165 is formed over thesubstrate surface 164 of the array. This dielectric can be one of the two specific dielectrics described above with respect to FIGS. 6A-B. Anotherdielectric layer 167 is formed between the two sets of conductive gates where they cross each other. This layer is made to be relatively thick in order to sustain the potential voltage differences between the two sets of gates, such as a 250 Angstroms thick oxide. - It will be noted from FIG. 8A, and the enlarged sectional view of one memory cell thereof in FIG. 9, that the length of the individual memory cell channels is divided into two portions that are field coupled with different ones of the two sets of control gates. The
word line 160 lies over the left approximately one-half of the channel length and thecontrol gate 157 over the other. Thecharge storing dielectric 165 is sandwiched between thesubstrate surface 164 and these gates A primary difference in operation of this array from that of the first example is that charge may be stored in two spatially separatedregions layer 165, and each of these regions may be individually programmed and read independently of the other. Programming by source side injection is preferred, which causes thecharge storage region 171 to be located adjacent an interior edge of thegate 160 and thecharge storage region 173 adjacent an interior edge of thegate 157. However, if programmed by channel hot-electron injection, electrons are stored inregions 172 and 174 within thelayer 165 instead of in theregions regions 172 and 174 are adjacent respective ones of the cell diffusions 152 and 153. - This example cell effectively contains two charge storage elements over its channel between adjacent source and drain
regions conductive gate 160 and the other under theconductive gate 157. Thedielectric layer 165 may be limited to these areas or, as is usually more convenient, extended over more of the array. FIGS. 7-9 show thecharge storage layer 165 extending over the entire array. - A
curve 175 of FIG. 9 illustrates the varying threshold voltage characteristics (VT) across the cell's channel, when programmed in theregions region 171 imparts a VT value 177 of the threshold under it, and the amount of charge stored in theregion 173 imparts a VT value 179 of the threshold under it. Each of the threshold values 177 and 179 may be maintained in one of two storage states, where a single breakpoint threshold value is set between the states. Two bits of data are stored in each cell if this is done. Alternatively, each of thevalues levels curve 175 is modified by thelevels charge storage regions 172 and 174. - Each of the threshold values177 and 179 is preferably programmed and read independently of one another. One segment of the cell is turned on hard, thus eliminating any effect of its programmed threshold level, while the other is being programmed or read. Although the specific voltages applied to the array will depend upon its specific structure, the following are approximate voltages that might be used for programming the cell of FIG. 9 by channel hot-electron injection:
- Programming the left segment, threshold value177: Substrate 163: 0 volts; source 153: VS=0 volts; drain 152: VD=5 volts; control gate 157: VSG=8 volts; and word line 160: VWL=10 volts.
- Programming the right segment, threshold value179: Substrate 163: 0 volts; source 152: VS=0 volts; drain 153: VD=5 volts; control gate 157: VSG=8 volts; and word line 160: VWL=10 volts.
- Programming is also preferably accomplished in this example by alternately pulsing a plurality of cells with these voltages in parallel and verifying their programmed states by reading them, the programming being terminated on a cell-by-cell basis after reaching the desired level, as done with floating gate flash memory gate arrays.
- Exemplary reading voltages for the cell of FIG. 9, when programmed in the manner described above, are as follows:
- Reading forward the left segment,
threshold value 177 by sensing the value of the cell current ICELL at fixed voltages: Substrate 163: 0 volts; source 153: VS=0 volts; drain 152: VD=1 volt; control gate 157: VSG=8 volts; and word line 160: VWL=6 volts. - Reading forward the right segment,
threshold value 179 by sensing the value of the cell current ICELL at fixed voltages: Substrate 163: 0 volts; source 152: VS=0 volts; drain 153: VD=1 volt; control gate 157: VSG=6 volts; and word line 160: VWL=8 volts. - Erasing of the memory cells is accomplished in this and the other two examples by the injection of holes into their charge trapping layers. These holes neutralize the negative charge of the electrons that were injected into the charge-trapping layer during a programming operation. It is the
layer 165 in this second example (FIGS. 7-9) that receives the electrons during programming and the holes during erasing. There are two specific erasing techniques. In one, the holes are injected into a charge storage portion of thelayer 165 from the silicon substrate by tunneling through an oxide portion of that layer that is in contact with the substrate surface, termed a “channel erase.” To bring this about, a negative potential is applied to the word line with respect to the substrate, with the drain and source either being grounded or left floating. In the other technique, the holes are injected into thelayer 165 from a region of the substrate near the drain or the source. In this second approach, referring to FIGS. 8 and 9, a combination of a negative voltage on both the word lines 159-161 and steering gates 155-157, and a positive voltage on the drains and sources 151-153, are applied. (In the cell shown in FIG. 3 for the first example previously described, a positive voltage is applied to thedrain 105, thesource 104 is left floating, and a negative voltage is applied to theword line 110.) - When cells have been programmed by source side injection, the channel erase technique is preferred. When programmed by the hot-electron injection technique, either of these two erasing techniques can be used. But when cells have been programmed by hot-electron injection, the channel erase has a disadvantage of tunneling holes across the entire channel, the result being an over erase of a portion of the charge trapping layer that does not contain electrons trapped by prior programming. This can cause the flat zero portions of the curve175 (FIG. 9) across the cell channel to be lowered to negative threshold values.
- To simultaneously erase a plurality of cells in a block of cells in this second example, the following voltages are simultaneously applied to individual cells: Substrate163: 0 volts; source 152: VS=5 volts; drain 153: VD=5 volts; control gate 157: VSG=−8 volts; and word line 160: VWL=−8 volts. These voltages implement the second erase approach described above.
- The memory cell array of FIGS.7-9 may also be formed by standard processing techniques, particularly those developed for making flash EEPROM arrays of the type utilizing a floating gate. In one example process, the
layer 165 is first formed over the entire substrate area of the memory cell array. A first layer of polysilicon is then deposited over this area and etched through an appropriate mask to leave the control gates 155-157. Thelayer 165 in between the control gates 155-157 is removed as part of this etching process, in one example. The source and drainregions layer 165 is then formed on thesubstrate surface 164 in between the control gates 155-157 and simultaneously over the top and sides of the control gates 155-157. This is a continuous layer of ONO (FIG. 6A) or silicon rich oxide (FIG. 6B). Thelayer 167 shown in FIGS. 8 and 9 can be part of thesame layer 165 or a combination of thelayer 165 and other dielectric material. Such other dielectric material can be in the form of oxide spacers (not shown) formed along the vertical walls of the control gates 155-157 and/or a thick oxide layer (not shown) on the top surface of the control gates 155-157. This top surface oxide is preferably formed by depositing the oxide on the top of the first polysilicon layer before it is separated into the gates 155-157. A second layer of polysilicon is then formed over this continuous layer, and is then etched into the word lines 159, 160 and 161. - It will be noted that this second example memory cell has a larger dimension in the x-direction by one resolution element than does the first example of FIGS.1-3, because of the added control (steering) gates 155-157. A second polysilicon layer is also required in this second example. This added structure and size, however, allows the amount of data that is stored in each cell to be doubled.
- A useful modification of the cell of FIGS.7-9 for some purposes replaces the electron storage layer under the control gates 155-157 with a thin (such as 200 Angstroms thick) gate dielectric, usually an oxide grown on the
substrate surface 164. This eliminates the secondelectron storage region 173 but adds an independent select transistor function to each cell. Erase can then be confined to individual rows of cells. - Third Memory Cell Example
- In this example, shown in FIGS.10-13, an array of Dual Storage Element Cells, described above in the Background, is provided with its conductive floating gates replaced by portions of one of the dielectric charge trapping material layers described above with respect to FIGS. 6A-6B. The making and operation of this array are similar to the arrays of Dual Storage Element Cells described in the patents and patent applications incorporated above into the Background and Summary.
- FIGS.10-12 show an array. Source and drain
diffusions surface 181 of asemi-conductive substrate 183, and have their lengths extending in the y-direction and are spaced apart in the x-direction. As apparent from the plan view of FIG. 10,conductive steering gates - As illustrated in the sectional views of FIGS. 11A and 11B, the steering gates189-194 are positioned over a
layer 201 of charge storage material according to one of FIGS. 6A-6B. After the steering gates 189-194 are formed over thecharge trapping layer 201, strips of that layer extending in the y-direction are removed between every other of the steering gates in the x-direction. The source and drain regions 185-187 are implanted between the remaining regions between every other steering gate in the x-direction. Anoxide layer 203 is formed over the tops and sides of the steering gates 189-194 to isolate those steering gates from the word lines 197-199, and simultaneously formed over the exposedsubstrate surface 181 to provide gate oxide under the word lines 197-199. An example thickness of thedielectric layer 203 is 200 Angstroms over the doped polysilicon steering gates 189-194, and 150 Angstroms on thesubstrate surface 181. The portions of theword line 198 shown in FIG. 11A, for example, that are formed immediately over the portion of theoxide layer 203 on thesubstrate surface 181, serve as the select transistor gates in that row of memory cells. - Adjacent pairs of steering gates on either side of the diffusions185-187 are preferably electrically connected together at a decoder for the steering gates in order to reduce the complexity of the decoder. One such pair includes steering
gates - Individual storage elements can be defined to exist in regions of the
dielectric trapping layer 201 under one of the steering gates 189-194 where one of the word lines 197-199 crosses, as shown in cross-hatching in the plan view of FIG. 10. There are two such storage elements per memory cell. Each storage element can be operated in two states (binary) in order to store 1 bit per storage element. The storage elements may alternatively be operated to individually store more than two states, such as four states per storage element, in a manner similar to that described in the Dual Storage Element Cell U.S. Pat. No. 6,151,248. The operation of such a dielectric storage memory array is similar to what is described in that patent, one difference being the use of lower voltages on the steering gates since there are no floating gates. - With reference to FIG. 12, an enlarged view of one of the memory cells of FIG. 11A is given. Charge is trapped within the
dielectric layer 201 in tworegions select transistor gate 198′ that is part of theword line 198, if programmed by the source-side injection technique. If programmed by the channel hot-electron injection technique, on the other hand, these charge regions are located adjacent the source and drainregions select transistor gate 198′ and beneath theword line 198 define the two storage elements of the cell that replace the two conductive floating gates of the Dual Storage Element Cell arrays and systems referenced above. Thedielectric layer 201, however, can extend beyond these storage elements. In one form, thelayer 201 is formed in strips having individual widths that extends in the x-direction between select transistors of memory cells in adjacent columns and lengths that extend in the y-direction across a large number of rows of memory cells. These strips, and the select transistor gate dielectric between them, can be self-aligned with edges of the steering gates, such as the edges of thesteering gates - The effect of charge stored in the
regions threshold voltage curve 215 of FIG. 12, similar to the other two examples described above, when programmed by source side injection. Acurve portion 217 indicates a variation of the threshold voltage VT of a portion of the memory cell channel under thecharge region 211. Similarly, the effect of thecharge region 213 on the channel is indicated by theportion 219 of thecurve 215. Each of these regions may be operated in two states (storing one bit per cell) or more than two states (storing more than one bit per cell), as previously described above for the other examples. If programmed by channel hot-electron injection, on the other hand, thecurve portions layer 201 that is mentioned above. - FIG. 13 shows an optional modification of the memory cell shown in cross-section of FIGS. 11A and 12. The difference is that the select gate portion of the
word line 198′ extends into a groove orrecess 221 in thesubstrate 183, with the select transistor gate dielectric 205′ formed between them along the bottom and walls of thegroove 221. This structure increases the length of the channel of the select transistor without taking any additional area across thesubstrate surface 181. - Although the gates in the foregoing structure are preferably made of doped polysilicon material, other suitable electrically conductive materials may be used in place of one or both of the polysilicon layers described. The second layer, for example, from which the word lines197-199 are formed, may be a polycide material, which is polysilicon with a conductive refractive metal silicide, such as tungsten, on its top surface in order to increase its conductivity. A polycide material is usually not preferred for the first conductive layer from which the steering gates 189-194 are formed because an oxide grown from a polycide as an interpoly dielectric is of lower quality than that grown from polysilicon. The same considerations apply for the second memory cell example described above. For the first memory cell example, since only one layer of conductive gates is formed, those gates may be a polycide material.
- Memory System Operation, in General
- An example memory system in which the various aspects of the present invention may be implemented is generally illustrated in the block diagram of FIG. 14. This system is most specifically directed to use of the second and third example arrays discussed above with control (steering) gates elongated in the y-direction but also has application to the first example by elimination of the circuits that connect to steering gates.
- A large number of individually
addressable memory cells 11 are arranged in a regular array of rows and columns, although other physical arrangements of cells are certainly possible. Bit lines, designated herein to extend along columns of thearray 11 of cells, are electrically connected with a bit line decoder anddriver circuit 13 throughlines 15. Word lines, which are designated in this description to extend along rows of the array I 11 of cells, are electrically connected throughlines 17 to a word line decoder anddriver circuit 19. Steering gates, which extend along columns of memory cells in thearray 11, are electrically connected to a steering gate decoder anddriver circuit 21 throughlines 23. The steering gates and/or bit lines may be connected to their respective decoders by techniques described in a co-pending patent application by Harari et al. entitled “Steering Gate and Bit Line Segmentation in Non-Volatile Memories,” U.S. Ser. No. 09/871,333, filed May 31, 2001, which application is incorporated herein by this reference. Each of thedecoders bus 25 from amemory controller 27. The decoder and driving circuits are also connected to thecontroller 27 over respective control andstatus signal lines bus 22 that interconnects the steering gates and bit line decoder anddriver circuits - The
controller 27 is connectable throughlines 35 to a host device (not shown). The host may be a personal computer, notebook computer, digital camera, audio player, various other hand held electronic devices, and the like. The memory system of FIG. 14 will commonly be implemented in a card according to one of several existing physical and electrical standards, such as one from the PCMCIA, the CompactFlash™ Association, the MMC™ Association, and others. When in a card format, thelines 35 terminate in a connector on the card that interfaces with a complementary connector of the host device. The electrical interface of many cards follows the ATA standard, wherein the memory system appears to the host as if it was a magnetic disk drive. Other memory card interface standards also exist. Alternatively to the card format, memory systems of the type shown in FIG. 14 are permanently embedded in the host device. - The decoder and
driver circuits array 11, as addressed over thebus 25, according to control signals in respective control andstatus lines array 11 to thecontroller 27 over the same control andstatus lines circuit 13 receive current or voltage levels that are indicative of the states of addressed memory cells within thearray 11, and provides thecontroller 27 with information about those states overlines 41 during a read operation. A large number of such sense amplifiers are usually used in order to be able to read the states of a large number of memory cells in parallel. During reading and program operations, one row of cells is typically addressed at a time through thecircuits 19 for accessing in the addressed row a number of cells that are selected by thecircuits - Operation of a memory system such as illustrated in FIG. 14 is described in patents and pending applications identified above, and in other patents and pending applications assigned to SanDisk Corporation, assignee of the present application. Those of the cited references that describe the structure, processing or operation of a memory system using floating gates as the storage elements will be recognized as being relevant to implementing the systems using dielectric storage elements in place of the floating gates. In addition, U.S. patent application Ser. No. 09/793,370, filed Feb. 26, 2001, describes a data programming method applied to either floating gate or dielectric storage element systems, which application is incorporated herein by this reference.
- Fourth Memory Cell Example
- A fourth example, illustrated in FIGS.15-17, applies the dielectric storage techniques to a NAND array, the floating gate version of which is generally described in the Background above. Conductive word lines 241-244, elongated in the x-direction and spaced apart in the y-direction, extend across strips 245-249 of charge storage dielectric and intermediate isolation regions 251-254 formed of dielectric in trenches of the
semi-conductor substrate 257, as best seen in the cross-section of FIG. 16A. The dielectric strips 245-249 are elongated in the y-direction and spaced apart in the x-direction with one of the dielectric isolation strips 251-254 positioned therebetween. The dielectric strips 251-254 are preferably formed by typical silicon trench isolation (STI) techniques. Alternative techniques for providing electrical isolation between adjacent columns of memory cells may be used instead. - The dielectric strips245-249 are formed directly on the surface of the
substrate 257. The dielectric material and other characteristics are preferably those of one of the two described above with respect to FIGS. 6A and 6B. The word lines 241-244 are, in turn, positioned directly on top of these dielectric strips in regions that become charge storage regions. Charge storage regions 265-267 are indicated in FIG. 16A along theword line 242, andregions dielectric strip 246. Doped source and drain regions are formed in surface areas of thesubstrate 257 between the word lines and the isolation dielectric. For example, source and drain regions 261-263 are positioned in between word lines of a column formed between dielectric isolation strips 251 and 252. This column forms one string of series connected memory cells, as shown in the cross-sectional view of FIG. 16B and represented by an electrical equivalent circuit diagram in FIG. 17. At each end of the string is a switching select transistor, shown in FIG. 16B at one end to have agate 275 and at the other end to have agate 277.Terminals - FIGS.15-16B illustrate the use of dielectric charge storage material in one specific NAND memory cell array structure. It will be recognized that dielectric charge storage material may also serve as charge storage elements in other specific NAND array structures.
- Typically in existing NAND arrays of memory cells with conductive floating gate storage elements, a group of memory cells, one cell in each of several such column strings that is in a selected common row, are selected for simultaneous reading or programming. The row is selected by placing appropriate voltages on the word lines. During a reading operation, the word lines of the rows within the associated NAND strings are raised to a relatively high voltage in order to render the memory cell transistors in those rows along each of the involved strings highly conductive, with the exception of the one row of cells that is desired to be read. During a programming operation, the voltage of the word line of the selected row in the associated NAND strings is raised to a higher voltage compared with the word lines of the non-selected rows of the associated NAND strings. Likewise, the select transistors at the ends of the strings of selected columns of cells are appropriately biased and appropriate voltages applied to their end terminals in order to carry out the desired reading or programming function. The same procedure can be applied to a NAND array of memory cells with dielectric storage media, such as that of FIGS.15-17.
- As with the other examples previously described, charge stored in the dielectric of a memory cell affects the threshold voltage of that cell. For example, the level of charge stored in the
region 265 of thedielectric strip 246 establishes the threshold voltage level of the memory cell transistor formed by that region, the adjacent source and drainregions word line 242 positioned over the channel. Each of the memory cell charge storage regions may be operated in two states or in more than two states, as previously described above for the other examples. - One process for forming the NAND structure illustrated in FIGS.15-16B includes first forming a layer of the charge storage dielectric material such as ONO over the entire area of the substrate to be occupied by the array. A mask of silicon nitride material is formed on top of the ONO layer to define parallel, elongated trenches in the substrate used to isolate adjacent NAND strings. An etching step then removes the dielectric layer and forms trenches in the substrate through openings of the mask. Silicon oxide is then deposited over the structure to fill in the trenches and openings of the mask. Excess oxide is removed, followed by removal of the silicon nitride mask material. The result is the structure shown in FIGS. 16A and 16B without the word lines (WLs). The word lines are then formed by depositing a layer of doped polysilicon material over at least the array area and then etching away portions of the material through another mask in order to leave the word lines as shown in FIGS. 16A and 16B. An ion implant can then be made through the charge storage dielectric layer into regions of the substrate that remain exposed between the thick isolation dielectric and the word lines, thereby to form the source and drain regions.
- Another process for forming a slightly different NAND dielectric storage array is illustrated by FIGS. 18A, 18B and18C. These views show the development of the structure along section VII-VII of the plan view of FIG. 15. Reference numbers of elements of FIGS. 18A-18C that correspond to elements of FIGS. 15-16B are the same with a double prime (″) added.
- In a first series of processing steps illustrated in FIG. 18A, a layer of silicon nitride is deposited on the surface of the
substrate 257″, usually after growing athin layer 296 of silicon dioxide on thesubstrate surface 257″. A mask is then formed on the nitride layer with openings elongated in the y-direction (FIG. 15) and the nitride layer is etched away through the mask to leave nitride strips 291-295 that are elongated in the y-direction and spaced apart in the x-direction. The substrate is then etched in the spaces between the nitride strips that serve as a mask, thereby forming isolation trenches in the substrate. Those trenches (FIG. 18B) are then filled with silicon oxide by depositing a thick oxide layer over the structure and then removing it to leave theportions 251″, 252″, 253″and 254″that fill the substrate trenches and extend slightly above the substrate surface. - A next series of steps is illustrated by FIG. 18C. The nitride strips291-295 are removed by a selective etch that leaves the trench oxide between them and the substrate surface under them mostly unaffected. A
layer 297 of charge storage dielectric, such as ONO, is then formed over the entire memory cell array area, covering the exposed substrate surface areas and the portions of the isolation dielectric extending above the substrate surface. Word lines are then formed by depositing a layer of doped polysilicon material over the entire area, forming a mask on top of the polysilicon layer with openings that are elongated in the x-direction and spaced apart in the y-direction, and then removing the polysilicon though the mask openings. This leaves the word lines extending across the structure, including theword line 242″of FIG. 18C. Source and drain regions of the substrate (not shown in the views of FIGS. 18A-18C) can then be implanted through the chargestorage dielectric layer 297 between the word lines and isolation oxide that serve as an implant mask. - It can be noted that the resulting structure of FIG. 18C has its charge
storage dielectric layer 297 extending over the entire array area, while that of FIGS. 16A and 16B limits this dielectric layer to strips in between the thick isolation dielectric layers. In either case, a charge storage dielectric layer is provided over the channels of the NAND storage transistors where it is need to store charge. - Memory System Utilizing an Array of the Fourth Example Memory Cell
- Another example memory system in which the various aspects of the present invention may be implemented is illustrated by the block diagram of FIG. 19.
Memory cell array 1 including a plurality of memory cells arranged in a matrix is controlled by acolumn control circuit 2, arow control circuit 3, a c-source control circuit 4 and a c-p-well control circuit 5. This system is particularly suited to use amemory cell array 1 that is of the NAND type described above with respect to FIGS. 15-18. Acontrol circuit 2 is connected to bit lines (BL) of thememory cell array 1 for reading data stored in the memory cells, for establishing a state of the memory cells during a program operation, and for controlling potential levels of the bit lines (BL) to promote the programming or to inhibit the programming. One terminal of each string of NAND memory cells described above, for example, can be connected to one of the bit lines, and the other terminal of the string to a common potential such as ground. Therow control circuit 3 is connected to word lines (WL) to apply reading or programming voltages to the word lines. These voltages, combined with the bit line potential levels controlled by thecolumn control circuit 2, cause selected memory cells along one of the word lines to be read or programmed in parallel. An erase voltage is also applied by thecircuits 2 to a p-type region on which the memory cells are formed. The c-source control circuit 4 controls a common source line (labeled as “c-source” in FIG. 18) connected to the memory cells. The c-p-well control circuit 5 controls the c-p-well voltage. - The data stored in the memory cells are read out by the
column control circuit 2 and are output to external I/O lines 51 via internal I/O lines 53 and a data input/output buffer 6. Program data to be stored in the memory cells are input to the data input/output buffer 6 via the external I/O lines 51, and transferred to thecolumn control circuit 2. The external I/O lines 51 are connected to acontroller 43. The controller includes various types of registers and other memory including a volatile random-access-memory (RAM) 45. - Command data for controlling the flash memory device are inputted to command
circuits 7 throughinternal control lines 55 throughexternal control lines 57 that are connected with thecontroller 43. The command data informs the flash memory of what operation is requested. The input command is transferred to astate machine 8 that controls thecolumn control circuit 2, therow control circuit 3, the c-source control circuit 4, the c-p-well control circuit 5 and the data input/output buffer 6. Thestate machine 8 can output a status data of the flash memory such as READY/BUSY or PASS/FAIL. - The
controller 43 is connected to, or connectable with, a host system such as a personal computer, a digital camera, or a personal digital assistant. It is the host that initiates commands, such as to store or read data to or from thememory array 1, and provides or receives such data, respectively. The controller converts such commands into command signals that can be interpreted and executed by thecommand circuits 7. The controller also typically contains buffer memory for the user data being written to or read from the memory array. A typical memory system includes one integratedcircuit chip 47 that includes thecontroller 43, and one or moreintegrated circuit chips 49 that each contain a memory array and associated control, input/output and state machine circuits. The trend, of course, is to integrate the memory array and controller circuits of a system together on one or more integrated circuit chips. - Either of the memory systems of FIG. 14 or FIG. 19 may be embedded as part of the host system, or may be included in a memory card that is removably insertible into a mating socket of a host system. Such a card may include the entire memory system. Alternatively, the controller and memory array (with associated peripheral circuits) may be provided in separate cards. Several card implementations are described, for example, in U.S. Pat. No. 5,887,145, which patent is expressly incorporated herein in its entirety by this reference.
- Other Memory Cell Configurations
- Other configurations of memory cell arrays that use conductive floating gates may similarly be modified to replace the floating gates with charge trapping dielectric material, and then to operate each charge storage region of the array either in binary (two states) or multi-states (more than two states). For example, certain configurations described in patents and patent applications referenced above position either of the storage elements or source/drain diffusions in trenches, the trenches either being rectangular in cross-section or V-shaped. In these embodiments, the conductive storage elements can also be replaced with charge trapping dielectric material.
- Conclusion
- Although the various aspects of the present invention have been described with respect to specific examples thereof, it will be understood that the invention is entitled to protection within the full scope of the appended claims.
Claims (31)
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CNB028265963A CN100539195C (en) | 2001-10-31 | 2002-10-31 | Nonvolatile memory array, Nonvolatile memory system and its formation method |
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Cited By (23)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20040080984A1 (en) * | 2002-10-25 | 2004-04-29 | Swift Craig T. | Erase of a memory having a non-conductive storage medium |
US20040136240A1 (en) * | 2003-01-14 | 2004-07-15 | Wei Zheng | Memory device having high work function gate and method of erasing same |
US20040208057A1 (en) * | 2003-04-15 | 2004-10-21 | Hamilton Darlene G. | Method of programming dual cell memory device to store multiple data states per cell |
US20050001232A1 (en) * | 2003-07-02 | 2005-01-06 | Micron Technology, Inc. | High-performance one-transistor memory cell |
US20050026353A1 (en) * | 2002-08-30 | 2005-02-03 | Micron Technology, Inc. | One transistor SOI non-volatile random access memory cell |
US20050036368A1 (en) * | 2003-07-21 | 2005-02-17 | Yeh Chih Chieh | Method for programming programmable eraseless memory |
US20050037546A1 (en) * | 2003-07-21 | 2005-02-17 | Yeh Chih Chieh | Method for manufacturing a programmable eraseless memory |
US20050099849A1 (en) * | 2003-11-07 | 2005-05-12 | Lutze Jeffrey W. | Flash memory programming using gate induced junction leakage current |
US20050157551A1 (en) * | 2001-10-31 | 2005-07-21 | Eliyahou Harari | Multi-state non-volatile integrated circuit memory systems that employ dielectric storage elements |
US20050185466A1 (en) * | 2004-02-24 | 2005-08-25 | Micron Technology, Inc. | Multi-state memory cell with asymmetric charge trapping |
US20050190601A1 (en) * | 2003-07-21 | 2005-09-01 | Macronix International Co. Ltd | Programmable resistor eraseless memory |
US20050250261A1 (en) * | 2002-08-30 | 2005-11-10 | Micron Technology, Inc. | One transistor SOI non-volatile random access memory cell |
US6995423B2 (en) | 2003-01-14 | 2006-02-07 | Advanced Micro Devices, Inc. | Memory device having a P+ gate and thin bottom oxide and method of erasing same |
US20060054964A1 (en) * | 2004-09-15 | 2006-03-16 | Mark Isler | Semiconductor device and method for fabricating a region thereon |
WO2006030380A1 (en) * | 2004-09-15 | 2006-03-23 | Koninklijke Philips Electronics N.V. | A sonos memory device with optimized shallow trench isolation |
US20060110880A1 (en) * | 2004-11-23 | 2006-05-25 | Yuan Jack H | Self-aligned trench filling with high coupling ratio |
US20060108647A1 (en) * | 2004-11-23 | 2006-05-25 | Yuan Jack H | Self-aligned trench filling for narrow gap isolation regions |
US20070069284A1 (en) * | 2004-09-09 | 2007-03-29 | Macronix International Co., Ltd. | Method and Apparatus for Operating a String of Charge Trapping Memory Cells |
US20070132010A1 (en) * | 2005-12-09 | 2007-06-14 | Micron Technology, Inc. | Enhanced multi-bit non-volatile memory device with resonant tunnel barrier |
US20080137418A1 (en) * | 2004-09-09 | 2008-06-12 | Macronix International Co., Ltd. | Method and Apparatus for Sensing In Charge Trapping Non-Volatile Memory |
US20090162977A1 (en) * | 2007-12-19 | 2009-06-25 | Vinod Robert Purayath | Non-Volatile Memory Fabrication And Isolation For Composite Charge Storage Structures |
US20110303968A1 (en) * | 2010-04-07 | 2011-12-15 | Macronix International Co., Ltd. | Nonvolatile Memory Array With Continuous Charge Storage Dielectric Stack |
US20130003459A1 (en) * | 2011-06-28 | 2013-01-03 | Seagate Technology Llc | Read Error Recovery for Solid-State Memory Based on Cumulative Background Charges |
Families Citing this family (19)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6542407B1 (en) | 2002-01-18 | 2003-04-01 | Sandisk Corporation | Techniques of recovering data from memory cells affected by field coupling with adjacent memory cells |
JP2003309194A (en) * | 2002-04-18 | 2003-10-31 | Nec Electronics Corp | Semiconductor storage device and its manufacturing method |
US6906376B1 (en) * | 2002-06-13 | 2005-06-14 | A Plus Flash Technology, Inc. | EEPROM cell structure and array architecture |
JP4412903B2 (en) * | 2002-06-24 | 2010-02-10 | 株式会社ルネサステクノロジ | Semiconductor device |
US6781877B2 (en) | 2002-09-06 | 2004-08-24 | Sandisk Corporation | Techniques for reducing effects of coupling between storage elements of adjacent rows of memory cells |
US7050330B2 (en) * | 2003-12-16 | 2006-05-23 | Micron Technology, Inc. | Multi-state NROM device |
US20050251617A1 (en) * | 2004-05-07 | 2005-11-10 | Sinclair Alan W | Hybrid non-volatile memory system |
US20060007732A1 (en) * | 2004-07-06 | 2006-01-12 | Macronix International Co., Ltd. | Charge trapping non-volatile memory and method for operating same |
US20060197144A1 (en) * | 2005-03-01 | 2006-09-07 | Mammen Thomas | Nitride storage cells with and without select gate |
TWI271827B (en) * | 2005-11-11 | 2007-01-21 | Powerchip Semiconductor Corp | Non-volatile memory and manufacturing method and operating method thereof |
US7414889B2 (en) * | 2006-05-23 | 2008-08-19 | Macronix International Co., Ltd. | Structure and method of sub-gate and architectures employing bandgap engineered SONOS devices |
KR100771882B1 (en) * | 2006-09-06 | 2007-11-01 | 삼성전자주식회사 | Program method for multi-level non-volatile memory device |
US7961511B2 (en) * | 2006-09-26 | 2011-06-14 | Sandisk Corporation | Hybrid programming methods and systems for non-volatile memory storage elements |
JP5558695B2 (en) * | 2008-11-18 | 2014-07-23 | 株式会社東芝 | Nonvolatile semiconductor memory device |
US9312017B2 (en) * | 2014-01-15 | 2016-04-12 | Apple Inc. | Storage in charge-trap memory structures using additional electrically-charged regions |
US9123575B1 (en) * | 2014-07-21 | 2015-09-01 | Avalanche Technology, Inc. | Semiconductor memory device having increased separation between memory elements |
US9548448B1 (en) | 2015-11-12 | 2017-01-17 | Avalanche Technology, Inc. | Memory device with increased separation between memory elements |
US10431576B1 (en) | 2018-04-20 | 2019-10-01 | Taiwan Semiconductor Manufacturing Company, Ltd. | Memory cell array and method of manufacturing same |
US11744065B2 (en) | 2021-09-22 | 2023-08-29 | International Business Machines Corporation | Read-only memory for chip security that is MOSFET process compatible |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6054734A (en) * | 1996-07-26 | 2000-04-25 | Sony Corporation | Non-volatile memory cell having dual gate electrodes |
US6445030B1 (en) * | 2001-01-30 | 2002-09-03 | Advanced Micro Devices, Inc. | Flash memory erase speed by fluorine implant or fluorination |
US6670669B1 (en) * | 1999-08-10 | 2003-12-30 | Fujitsu Limited | Multiple-bit non-volatile memory utilizing non-conductive charge trapping gate |
Family Cites Families (103)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3979582A (en) | 1974-09-17 | 1976-09-07 | Westinghouse Electric Corporation | Discrete analog processing system including a matrix of memory elements |
JPS5346621B2 (en) | 1974-10-21 | 1978-12-15 | ||
US4112507A (en) | 1976-01-30 | 1978-09-05 | Westinghouse Electric Corp. | Addressable MNOS cell for non-volatile memories |
US4398248A (en) | 1980-10-20 | 1983-08-09 | Mcdonnell Douglas Corporation | Adaptive WSI/MNOS solid state memory system |
US4173766A (en) | 1977-09-16 | 1979-11-06 | Fairchild Camera And Instrument Corporation | Insulated gate field-effect transistor read-only memory cell |
US4527257A (en) | 1982-08-25 | 1985-07-02 | Westinghouse Electric Corp. | Common memory gate non-volatile transistor memory |
JPS59111370A (en) | 1982-12-16 | 1984-06-27 | Seiko Instr & Electronics Ltd | Nonvolatile semiconductor memory |
US5168334A (en) | 1987-07-31 | 1992-12-01 | Texas Instruments, Incorporated | Non-volatile semiconductor memory |
US4870470A (en) | 1987-10-16 | 1989-09-26 | International Business Machines Corporation | Non-volatile memory cell having Si rich silicon nitride charge trapping layer |
US5095344A (en) | 1988-06-08 | 1992-03-10 | Eliyahou Harari | Highly compact eprom and flash eeprom devices |
US5043940A (en) | 1988-06-08 | 1991-08-27 | Eliyahou Harari | Flash EEPROM memory systems having multistate storage cells |
US5070032A (en) | 1989-03-15 | 1991-12-03 | Sundisk Corporation | Method of making dense flash eeprom semiconductor memory structures |
US5172338B1 (en) | 1989-04-13 | 1997-07-08 | Sandisk Corp | Multi-state eeprom read and write circuits and techniques |
US5343063A (en) | 1990-12-18 | 1994-08-30 | Sundisk Corporation | Dense vertical programmable read only memory cell structure and processes for making them |
US5278439A (en) * | 1991-08-29 | 1994-01-11 | Ma Yueh Y | Self-aligned dual-bit split gate (DSG) flash EEPROM cell |
JPH0594699A (en) * | 1991-09-30 | 1993-04-16 | Hitachi Ltd | Semiconductor memory |
JPH05110114A (en) | 1991-10-17 | 1993-04-30 | Rohm Co Ltd | Nonvolatile semiconductor memory device |
JPH05129624A (en) * | 1991-11-06 | 1993-05-25 | Rohm Co Ltd | Semiconductor storage device |
JPH05129564A (en) * | 1991-11-06 | 1993-05-25 | Kawasaki Steel Corp | Semiconductor memory device and fabrication thereof |
US5313421A (en) | 1992-01-14 | 1994-05-17 | Sundisk Corporation | EEPROM with split gate source side injection |
US6222762B1 (en) | 1992-01-14 | 2001-04-24 | Sandisk Corporation | Multi-state memory |
US5712180A (en) | 1992-01-14 | 1998-01-27 | Sundisk Corporation | EEPROM with split gate source side injection |
US5315541A (en) | 1992-07-24 | 1994-05-24 | Sundisk Corporation | Segmented column memory array |
GB9217743D0 (en) | 1992-08-19 | 1992-09-30 | Philips Electronics Uk Ltd | A semiconductor memory device |
US5436481A (en) | 1993-01-21 | 1995-07-25 | Nippon Steel Corporation | MOS-type semiconductor device and method of making the same |
US5424978A (en) * | 1993-03-15 | 1995-06-13 | Nippon Steel Corporation | Non-volatile semiconductor memory cell capable of storing more than two different data and method of using the same |
US5555204A (en) | 1993-06-29 | 1996-09-10 | Kabushiki Kaisha Toshiba | Non-volatile semiconductor memory device |
US5887145A (en) | 1993-09-01 | 1999-03-23 | Sandisk Corporation | Removable mother/daughter peripheral card |
US5440505A (en) * | 1994-01-21 | 1995-08-08 | Intel Corporation | Method and circuitry for storing discrete amounts of charge in a single memory element |
US5661053A (en) | 1994-05-25 | 1997-08-26 | Sandisk Corporation | Method of making dense flash EEPROM cell array and peripheral supporting circuits formed in deposited field oxide with the use of spacers |
US5539690A (en) | 1994-06-02 | 1996-07-23 | Intel Corporation | Write verify schemes for flash memory with multilevel cells |
JP3635681B2 (en) | 1994-07-15 | 2005-04-06 | ソニー株式会社 | Bias circuit adjustment method, charge transfer device, charge detection device, and adjustment method thereof |
US5768192A (en) | 1996-07-23 | 1998-06-16 | Saifun Semiconductors, Ltd. | Non-volatile semiconductor memory cell utilizing asymmetrical charge trapping |
US6137718A (en) | 1996-08-01 | 2000-10-24 | Siemens Aktiengesellschaft | Method for operating a non-volatile memory cell arrangement |
US5889303A (en) * | 1997-04-07 | 1999-03-30 | Motorola, Inc. | Split-Control gate electrically erasable programmable read only memory (EEPROM) cell |
GB2325546B (en) | 1997-05-21 | 2001-10-17 | Motorola Inc | Electrically programmable memory and method of programming |
US6297096B1 (en) | 1997-06-11 | 2001-10-02 | Saifun Semiconductors Ltd. | NROM fabrication method |
US5824584A (en) | 1997-06-16 | 1998-10-20 | Motorola, Inc. | Method of making and accessing split gate memory device |
US5969383A (en) | 1997-06-16 | 1999-10-19 | Motorola, Inc. | Split-gate memory device and method for accessing the same |
IL125604A (en) | 1997-07-30 | 2004-03-28 | Saifun Semiconductors Ltd | Non-volatile electrically erasable and programmble semiconductor memory cell utilizing asymmetrical charge |
US6768165B1 (en) | 1997-08-01 | 2004-07-27 | Saifun Semiconductors Ltd. | Two bit non-volatile electrically erasable and programmable semiconductor memory cell utilizing asymmetrical charge trapping |
US5851881A (en) | 1997-10-06 | 1998-12-22 | Taiwan Semiconductor Manufacturing Company, Ltd. | Method of making monos flash memory for multi-level logic |
US5912844A (en) | 1998-01-28 | 1999-06-15 | Macronix International Co., Ltd. | Method for flash EEPROM data writing |
US6030871A (en) | 1998-05-05 | 2000-02-29 | Saifun Semiconductors Ltd. | Process for producing two bit ROM cell utilizing angled implant |
US6348711B1 (en) | 1998-05-20 | 2002-02-19 | Saifun Semiconductors Ltd. | NROM cell with self-aligned programming and erasure areas |
US6215148B1 (en) | 1998-05-20 | 2001-04-10 | Saifun Semiconductors Ltd. | NROM cell with improved programming, erasing and cycling |
US6346725B1 (en) * | 1998-05-22 | 2002-02-12 | Winbond Electronics Corporation | Contact-less array of fully self-aligned, triple polysilicon, source-side injection, nonvolatile memory cells with metal-overlaid wordlines |
US6281075B1 (en) | 1999-01-27 | 2001-08-28 | Sandisk Corporation | Method of controlling of floating gate oxide growth by use of an oxygen barrier |
US6181597B1 (en) | 1999-02-04 | 2001-01-30 | Tower Semiconductor Ltd. | EEPROM array using 2-bit non-volatile memory cells with serial read operations |
US6256231B1 (en) | 1999-02-04 | 2001-07-03 | Tower Semiconductor Ltd. | EEPROM array using 2-bit non-volatile memory cells and method of implementing same |
US6151248A (en) | 1999-06-30 | 2000-11-21 | Sandisk Corporation | Dual floating gate EEPROM cell array with steering gates shared by adjacent cells |
US6103573A (en) | 1999-06-30 | 2000-08-15 | Sandisk Corporation | Processing techniques for making a dual floating gate EEPROM cell array |
US6454528B2 (en) * | 1999-08-04 | 2002-09-24 | Mccabe Francis J. | Intake and exhaust damper with movable motor fan assembly |
US6255166B1 (en) * | 1999-08-05 | 2001-07-03 | Aalo Lsi Design & Device Technology, Inc. | Nonvolatile memory cell, method of programming the same and nonvolatile memory array |
US6388293B1 (en) | 1999-10-12 | 2002-05-14 | Halo Lsi Design & Device Technology, Inc. | Nonvolatile memory cell, operating method of the same and nonvolatile memory array |
US6091633A (en) | 1999-08-09 | 2000-07-18 | Sandisk Corporation | Memory array architecture utilizing global bit lines shared by multiple cells |
KR100343210B1 (en) | 1999-08-11 | 2002-07-10 | 윤종용 | MNOS series memory using single electron transistor and fabrication method thereof |
JP2001110918A (en) * | 1999-10-04 | 2001-04-20 | Fujitsu Ltd | Non-volatile semiconductor memory device |
JP2001148434A (en) * | 1999-10-12 | 2001-05-29 | New Heiro:Kk | Non-volatile memory cell and its usage, manufacturing method, and non-volatile memory array |
US6177318B1 (en) | 1999-10-18 | 2001-01-23 | Halo Lsi Design & Device Technology, Inc. | Integration method for sidewall split gate monos transistor |
US6406960B1 (en) | 1999-10-25 | 2002-06-18 | Advanced Micro Devices, Inc. | Process for fabricating an ONO structure having a silicon-rich silicon nitride layer |
US6248633B1 (en) | 1999-10-25 | 2001-06-19 | Halo Lsi Design & Device Technology, Inc. | Process for making and programming and operating a dual-bit multi-level ballistic MONOS memory |
US6429063B1 (en) | 1999-10-26 | 2002-08-06 | Saifun Semiconductors Ltd. | NROM cell with generally decoupled primary and secondary injection |
JP4923318B2 (en) * | 1999-12-17 | 2012-04-25 | ソニー株式会社 | Nonvolatile semiconductor memory device and operation method thereof |
US6215702B1 (en) | 2000-02-16 | 2001-04-10 | Advanced Micro Devices, Inc. | Method of maintaining constant erasing speeds for non-volatile memory cells |
US6266281B1 (en) | 2000-02-16 | 2001-07-24 | Advanced Micro Devices, Inc. | Method of erasing non-volatile memory cells |
US6331953B1 (en) | 2000-02-16 | 2001-12-18 | Advanced Micro Devices | Intelligent ramped gate and ramped drain erasure for non-volatile memory cells |
US6331952B1 (en) | 2000-02-16 | 2001-12-18 | Advanced Micro Devices, Inc. | Positive gate erasure for non-volatile memory cells |
US6349062B1 (en) | 2000-02-29 | 2002-02-19 | Advanced Micro Devices, Inc. | Selective erasure of a non-volatile memory cell of a flash memory device |
US6366501B1 (en) | 2000-02-29 | 2002-04-02 | Advanced Micro Devices, Inc. | Selective erasure of a non-volatile memory cell of a flash memory device |
US6888750B2 (en) | 2000-04-28 | 2005-05-03 | Matrix Semiconductor, Inc. | Nonvolatile memory on SOI and compound semiconductor substrates and method of fabrication |
JP3573691B2 (en) | 2000-07-03 | 2004-10-06 | シャープ株式会社 | Nonvolatile semiconductor memory device and method of manufacturing the same |
TW503528B (en) | 2000-07-12 | 2002-09-21 | Koninkl Philips Electronics Nv | Semiconductor device |
US6487121B1 (en) | 2000-08-25 | 2002-11-26 | Advanced Micro Devices, Inc. | Method of programming a non-volatile memory cell using a vertical electric field |
EP1215681B1 (en) | 2000-12-05 | 2008-04-16 | Halo Lsi Design and Device Technology Inc. | Program and erase methods in twin MONOS cell memories |
TW577082B (en) | 2000-12-15 | 2004-02-21 | Halo Lsi Inc | Fast program to program verify method |
JP4325972B2 (en) | 2001-01-30 | 2009-09-02 | セイコーエプソン株式会社 | Manufacturing method of semiconductor integrated circuit device including nonvolatile semiconductor memory device |
TW476144B (en) | 2001-02-02 | 2002-02-11 | Macronix Int Co Ltd | Non-volatile memory |
US6531350B2 (en) | 2001-02-22 | 2003-03-11 | Halo, Inc. | Twin MONOS cell fabrication method and array organization |
US6738289B2 (en) | 2001-02-26 | 2004-05-18 | Sandisk Corporation | Non-volatile memory with improved programming and method therefor |
US6418062B1 (en) | 2001-03-01 | 2002-07-09 | Halo Lsi, Inc. | Erasing methods by hot hole injection to carrier trap sites of a nonvolatile memory |
EP1246196B1 (en) | 2001-03-15 | 2010-02-17 | Halo, Inc. | Twin MONOS memory cell usage for wide program bandwidth |
KR100375235B1 (en) | 2001-03-17 | 2003-03-08 | 삼성전자주식회사 | Sonos flash memory device and a method for fabricating the same |
US6493266B1 (en) | 2001-04-09 | 2002-12-10 | Advanced Micro Devices, Inc. | Soft program and soft program verify of the core cells in flash memory array |
KR100389130B1 (en) | 2001-04-25 | 2003-06-25 | 삼성전자주식회사 | Non-Volatile Memory Device with 2 transistors for 2-bit operation |
US6936887B2 (en) | 2001-05-18 | 2005-08-30 | Sandisk Corporation | Non-volatile memory cells utilizing substrate trenches |
US6580120B2 (en) | 2001-06-07 | 2003-06-17 | Interuniversitair Microelektronica Centrum (Imec Vzw) | Two bit non-volatile electrically erasable and programmable memory structure, a process for producing said memory structure and methods for programming, reading and erasing said memory structure |
KR100395769B1 (en) | 2001-06-21 | 2003-08-21 | 삼성전자주식회사 | Erasing method in a non-volatile memory device |
DE10129958B4 (en) | 2001-06-21 | 2006-07-13 | Infineon Technologies Ag | Memory cell arrangement and manufacturing method |
US6436768B1 (en) | 2001-06-27 | 2002-08-20 | Advanced Micro Devices, Inc. | Source drain implant during ONO formation for improved isolation of SONOS devices |
DE60222504T2 (en) | 2001-07-06 | 2008-06-19 | Halo Lsi Design And Device Technology Inc. | Method of making self-aligning L-shaped sidewall spacers |
EP1274093A3 (en) | 2001-07-06 | 2004-12-08 | Halo Lsi Design and Device Technology Inc. | A control gate decoder for twin MONOS memory with two bit erase capability |
US6555865B2 (en) | 2001-07-10 | 2003-04-29 | Samsung Electronics Co. Ltd. | Nonvolatile semiconductor memory device with a multi-layer sidewall spacer structure and method for manufacturing the same |
KR100399350B1 (en) | 2001-08-09 | 2003-09-26 | 삼성전자주식회사 | Non volatile memory having floating trap type device and method of forming the same |
KR100407573B1 (en) | 2001-08-09 | 2003-11-28 | 삼성전자주식회사 | Method of forming non volatile memory having floating trap type device |
US6593624B2 (en) | 2001-09-25 | 2003-07-15 | Matrix Semiconductor, Inc. | Thin film transistors with vertically offset drain regions |
JP2003163292A (en) | 2001-08-13 | 2003-06-06 | Halo Lsi Inc | Twin nand device structure, its array operation and its fabricating method |
US6456528B1 (en) | 2001-09-17 | 2002-09-24 | Sandisk Corporation | Selective operation of a multi-state non-volatile memory system in a binary mode |
US6413821B1 (en) | 2001-09-18 | 2002-07-02 | Seiko Epson Corporation | Method of fabricating semiconductor device including nonvolatile memory and peripheral circuit |
KR100454117B1 (en) | 2001-10-22 | 2004-10-26 | 삼성전자주식회사 | Methods of operating a non-volatile memory device having a silicon-oxide-nitride-oxide-silicon (SONOS) gate structure |
DE10153384B4 (en) | 2001-10-30 | 2007-08-02 | Infineon Technologies Ag | Semiconductor memory cell, method for its production and semiconductor memory device |
DE10153561C2 (en) | 2001-10-30 | 2003-09-04 | Infineon Technologies Ag | Charge trapping memory cell, method for its production and semiconductor memory device |
US20030134476A1 (en) | 2002-01-17 | 2003-07-17 | Yakov Roizin | Oxide-nitride-oxide structure |
-
2001
- 2001-10-31 US US10/002,696 patent/US6897522B2/en not_active Expired - Lifetime
-
2002
- 2002-05-31 US US10/161,235 patent/US20030080370A1/en not_active Abandoned
- 2002-10-30 TW TW091132182A patent/TWI318786B/en not_active IP Right Cessation
- 2002-10-30 TW TW096151684A patent/TWI351699B/en not_active IP Right Cessation
- 2002-10-30 TW TW096151683A patent/TWI344195B/en not_active IP Right Cessation
- 2002-10-31 JP JP2003541063A patent/JP4846979B2/en not_active Expired - Fee Related
- 2002-10-31 AT AT07002288T patent/ATE441211T1/en not_active IP Right Cessation
- 2002-10-31 DE DE60233533T patent/DE60233533D1/en not_active Expired - Lifetime
- 2002-10-31 CN CN2007101358023A patent/CN101140799B/en not_active Expired - Lifetime
- 2002-10-31 AT AT07002289T patent/ATE493763T1/en not_active IP Right Cessation
- 2002-10-31 DE DE60238796T patent/DE60238796D1/en not_active Expired - Lifetime
- 2002-10-31 KR KR1020097025906A patent/KR101124259B1/en active IP Right Grant
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6054734A (en) * | 1996-07-26 | 2000-04-25 | Sony Corporation | Non-volatile memory cell having dual gate electrodes |
US6670669B1 (en) * | 1999-08-10 | 2003-12-30 | Fujitsu Limited | Multiple-bit non-volatile memory utilizing non-conductive charge trapping gate |
US6445030B1 (en) * | 2001-01-30 | 2002-09-03 | Advanced Micro Devices, Inc. | Flash memory erase speed by fluorine implant or fluorination |
Cited By (69)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20050157551A1 (en) * | 2001-10-31 | 2005-07-21 | Eliyahou Harari | Multi-state non-volatile integrated circuit memory systems that employ dielectric storage elements |
US20080116509A1 (en) * | 2001-10-31 | 2008-05-22 | Eliyahou Harari | Multi-State Non-Volatile Integrated Circuit Memory Systems that Employ Dielectric Storage Elements |
US20080119026A1 (en) * | 2001-10-31 | 2008-05-22 | Eliyahou Harari | Multi-State Non-Volatile Integrated Circuit Memory Systems that Employ Dielectric Storage Elements |
US7834392B2 (en) | 2001-10-31 | 2010-11-16 | Sandisk Corporation | Multi-state non-volatile integrated circuit memory systems that employ dielectric storage elements |
US20050180210A1 (en) * | 2001-10-31 | 2005-08-18 | Eliyahou Harari | Multi-state non-volatile integrated circuit memory systems that employ dielectric storage elements |
US6925007B2 (en) | 2001-10-31 | 2005-08-02 | Sandisk Corporation | Multi-state non-volatile integrated circuit memory systems that employ dielectric storage elements |
US7184312B2 (en) * | 2002-08-30 | 2007-02-27 | Micron Technology, Inc. | One transistor SOI non-volatile random access memory cell |
US20050250261A1 (en) * | 2002-08-30 | 2005-11-10 | Micron Technology, Inc. | One transistor SOI non-volatile random access memory cell |
US7339830B2 (en) | 2002-08-30 | 2008-03-04 | Micron Technology, Inc. | One transistor SOI non-volatile random access memory cell |
US20070138555A1 (en) * | 2002-08-30 | 2007-06-21 | Micron Technology, Inc. | One transistor SOI non-volatile random access memory cell |
US20050026353A1 (en) * | 2002-08-30 | 2005-02-03 | Micron Technology, Inc. | One transistor SOI non-volatile random access memory cell |
US7566601B2 (en) | 2002-08-30 | 2009-07-28 | Micron Technology, Inc. | Method of making a one transistor SOI non-volatile random access memory cell |
US6898129B2 (en) * | 2002-10-25 | 2005-05-24 | Freescale Semiconductor, Inc. | Erase of a memory having a non-conductive storage medium |
US20040080984A1 (en) * | 2002-10-25 | 2004-04-29 | Swift Craig T. | Erase of a memory having a non-conductive storage medium |
US20040136240A1 (en) * | 2003-01-14 | 2004-07-15 | Wei Zheng | Memory device having high work function gate and method of erasing same |
US6912163B2 (en) | 2003-01-14 | 2005-06-28 | Fasl, Llc | Memory device having high work function gate and method of erasing same |
US6995423B2 (en) | 2003-01-14 | 2006-02-07 | Advanced Micro Devices, Inc. | Memory device having a P+ gate and thin bottom oxide and method of erasing same |
US6956768B2 (en) * | 2003-04-15 | 2005-10-18 | Advanced Micro Devices, Inc. | Method of programming dual cell memory device to store multiple data states per cell |
US20040208057A1 (en) * | 2003-04-15 | 2004-10-21 | Hamilton Darlene G. | Method of programming dual cell memory device to store multiple data states per cell |
US20060244007A1 (en) * | 2003-07-02 | 2006-11-02 | Micron Technology, Inc. | High-performance one-transistor memory cell |
US7660144B2 (en) | 2003-07-02 | 2010-02-09 | Micron Technology, Inc. | High-performance one-transistor memory cell |
US8125003B2 (en) | 2003-07-02 | 2012-02-28 | Micron Technology, Inc. | High-performance one-transistor memory cell |
US7968402B2 (en) | 2003-07-02 | 2011-06-28 | Micron Technology, Inc. | Method for forming a high-performance one-transistor memory cell |
US20050001232A1 (en) * | 2003-07-02 | 2005-01-06 | Micron Technology, Inc. | High-performance one-transistor memory cell |
US7728350B2 (en) | 2003-07-02 | 2010-06-01 | Micron Technology, Inc. | Memory cell with negative differential resistance |
US20060245244A1 (en) * | 2003-07-02 | 2006-11-02 | Micron Technology, Inc. | High-performance one-transistor memory cell |
US20060246653A1 (en) * | 2003-07-02 | 2006-11-02 | Micron Technology, Inc. | High-performance one-transistor memory cell |
US20050036368A1 (en) * | 2003-07-21 | 2005-02-17 | Yeh Chih Chieh | Method for programming programmable eraseless memory |
US20050190601A1 (en) * | 2003-07-21 | 2005-09-01 | Macronix International Co. Ltd | Programmable resistor eraseless memory |
US8501591B2 (en) | 2003-07-21 | 2013-08-06 | Macronix International Co., Ltd. | Method for manufacturing a multiple-bit-per-cell memory |
US20050037546A1 (en) * | 2003-07-21 | 2005-02-17 | Yeh Chih Chieh | Method for manufacturing a programmable eraseless memory |
US7132350B2 (en) * | 2003-07-21 | 2006-11-07 | Macronix International Co., Ltd. | Method for manufacturing a programmable eraseless memory |
US7180123B2 (en) | 2003-07-21 | 2007-02-20 | Macronix International Co., Ltd. | Method for programming programmable eraseless memory |
WO2005027227A1 (en) * | 2003-09-09 | 2005-03-24 | Spansion Llc | Memory device and method of erasing the same |
US7057931B2 (en) | 2003-11-07 | 2006-06-06 | Sandisk Corporation | Flash memory programming using gate induced junction leakage current |
US20050099849A1 (en) * | 2003-11-07 | 2005-05-12 | Lutze Jeffrey W. | Flash memory programming using gate induced junction leakage current |
US20050185466A1 (en) * | 2004-02-24 | 2005-08-25 | Micron Technology, Inc. | Multi-state memory cell with asymmetric charge trapping |
US20060203555A1 (en) * | 2004-02-24 | 2006-09-14 | Micron Technology, Inc. | Multi-state memory cell with asymmetric charge trapping |
US7072217B2 (en) | 2004-02-24 | 2006-07-04 | Micron Technology, Inc. | Multi-state memory cell with asymmetric charge trapping |
US20100039869A1 (en) * | 2004-02-24 | 2010-02-18 | Micron Technology, Inc. | Multi-state memory cell with asymmetric charge trapping |
US7911837B2 (en) | 2004-02-24 | 2011-03-22 | Micron Technology, Inc. | Multi-state memory cell with asymmetric charge trapping |
US20060203554A1 (en) * | 2004-02-24 | 2006-09-14 | Micron Technology, Inc. | Multi-state memory cell with asymmetric charge trapping |
US7616482B2 (en) | 2004-02-24 | 2009-11-10 | Micron Technology, Inc. | Multi-state memory cell with asymmetric charge trapping |
US7577027B2 (en) | 2004-02-24 | 2009-08-18 | Micron Technology, Inc. | Multi-state memory cell with asymmetric charge trapping |
US20070069284A1 (en) * | 2004-09-09 | 2007-03-29 | Macronix International Co., Ltd. | Method and Apparatus for Operating a String of Charge Trapping Memory Cells |
US20080137418A1 (en) * | 2004-09-09 | 2008-06-12 | Macronix International Co., Ltd. | Method and Apparatus for Sensing In Charge Trapping Non-Volatile Memory |
US7483307B2 (en) * | 2004-09-09 | 2009-01-27 | Macronix International Co., Ltd. | Method and apparatus for sensing in charge trapping non-volatile memory |
US7366024B2 (en) * | 2004-09-09 | 2008-04-29 | Macronix International Co., Ltd. | Method and apparatus for operating a string of charge trapping memory cells |
US20060054964A1 (en) * | 2004-09-15 | 2006-03-16 | Mark Isler | Semiconductor device and method for fabricating a region thereon |
WO2006030380A1 (en) * | 2004-09-15 | 2006-03-23 | Koninklijke Philips Electronics N.V. | A sonos memory device with optimized shallow trench isolation |
US7923363B2 (en) * | 2004-09-15 | 2011-04-12 | Nxp B.V. | SONOS memory device with optimized shallow trench isolation |
US20090212347A1 (en) * | 2004-09-15 | 2009-08-27 | Koninklijke Philips Electronics N.V. | Sonos memory device with optimized shallow trench isolation |
US20060108648A1 (en) * | 2004-11-23 | 2006-05-25 | Yuan Jack H | Memory with self-aligned trenches for narrow gap isolation regions |
US7381615B2 (en) | 2004-11-23 | 2008-06-03 | Sandisk Corporation | Methods for self-aligned trench filling with grown dielectric for high coupling ratio in semiconductor devices |
US7402886B2 (en) | 2004-11-23 | 2008-07-22 | Sandisk Corporation | Memory with self-aligned trenches for narrow gap isolation regions |
US7416956B2 (en) | 2004-11-23 | 2008-08-26 | Sandisk Corporation | Self-aligned trench filling for narrow gap isolation regions |
US20060108647A1 (en) * | 2004-11-23 | 2006-05-25 | Yuan Jack H | Self-aligned trench filling for narrow gap isolation regions |
US7615820B2 (en) | 2004-11-23 | 2009-11-10 | Sandisk Corporation | Self-aligned trenches with grown dielectric for high coupling ratio in semiconductor devices |
US20060110880A1 (en) * | 2004-11-23 | 2006-05-25 | Yuan Jack H | Self-aligned trench filling with high coupling ratio |
US20090155970A1 (en) * | 2005-12-09 | 2009-06-18 | Micron Technology, Inc. | Enhanced multi-bit non-volatile memory device with resonant tunnel barrier |
US20070132010A1 (en) * | 2005-12-09 | 2007-06-14 | Micron Technology, Inc. | Enhanced multi-bit non-volatile memory device with resonant tunnel barrier |
US7867850B2 (en) * | 2005-12-09 | 2011-01-11 | Micron Technology, Inc. | Enhanced multi-bit non-volatile memory device with resonant tunnel barrier |
US7482651B2 (en) * | 2005-12-09 | 2009-01-27 | Micron Technology, Inc. | Enhanced multi-bit non-volatile memory device with resonant tunnel barrier |
US20090162977A1 (en) * | 2007-12-19 | 2009-06-25 | Vinod Robert Purayath | Non-Volatile Memory Fabrication And Isolation For Composite Charge Storage Structures |
US7888210B2 (en) * | 2007-12-19 | 2011-02-15 | Sandisk Corporation | Non-volatile memory fabrication and isolation for composite charge storage structures |
US20110303968A1 (en) * | 2010-04-07 | 2011-12-15 | Macronix International Co., Ltd. | Nonvolatile Memory Array With Continuous Charge Storage Dielectric Stack |
US8975687B2 (en) * | 2010-04-07 | 2015-03-10 | Macronix International Co., Ltd. | Nonvolatile memory array with continuous charge storage dielectric stack |
US20130003459A1 (en) * | 2011-06-28 | 2013-01-03 | Seagate Technology Llc | Read Error Recovery for Solid-State Memory Based on Cumulative Background Charges |
US8547743B2 (en) * | 2011-06-28 | 2013-10-01 | Seagate Technology Llc | Read error recovery for solid-state memory based on cumulative background charges |
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JP4846979B2 (en) | 2011-12-28 |
TW200924117A (en) | 2009-06-01 |
DE60238796D1 (en) | 2011-02-10 |
CN101140799A (en) | 2008-03-12 |
KR101124259B1 (en) | 2012-04-24 |
JP2005508094A (en) | 2005-03-24 |
CN101140799B (en) | 2011-06-08 |
ATE493763T1 (en) | 2011-01-15 |
US6897522B2 (en) | 2005-05-24 |
DE60233533D1 (en) | 2009-10-08 |
US20030082871A1 (en) | 2003-05-01 |
ATE441211T1 (en) | 2009-09-15 |
TWI351699B (en) | 2011-11-01 |
KR20100006170A (en) | 2010-01-18 |
TWI344195B (en) | 2011-06-21 |
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TW200406887A (en) | 2004-05-01 |
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