US20140092679A1 - Memory device and writing method thereof - Google Patents
Memory device and writing method thereof Download PDFInfo
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- US20140092679A1 US20140092679A1 US14/096,091 US201314096091A US2014092679A1 US 20140092679 A1 US20140092679 A1 US 20140092679A1 US 201314096091 A US201314096091 A US 201314096091A US 2014092679 A1 US2014092679 A1 US 2014092679A1
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- bit line
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
- G11C13/0004—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements comprising amorphous/crystalline phase transition cells
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
- G11C13/0021—Auxiliary circuits
- G11C13/0069—Writing or programming circuits or methods
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C7/00—Arrangements for writing information into, or reading information out from, a digital store
- G11C7/10—Input/output [I/O] data interface arrangements, e.g. I/O data control circuits, I/O data buffers
- G11C7/1078—Data input circuits, e.g. write amplifiers, data input buffers, data input registers, data input level conversion circuits
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C7/00—Arrangements for writing information into, or reading information out from, a digital store
- G11C7/10—Input/output [I/O] data interface arrangements, e.g. I/O data control circuits, I/O data buffers
- G11C7/1078—Data input circuits, e.g. write amplifiers, data input buffers, data input registers, data input level conversion circuits
- G11C7/1096—Write circuits, e.g. I/O line write drivers
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
- G11C13/0021—Auxiliary circuits
- G11C13/0069—Writing or programming circuits or methods
- G11C2013/0078—Write using current through the cell
Definitions
- This invention relates to a memory device and a writing method thereof.
- phase state of a phase change material such as chalcogenide can be changed between a crystalline state and an amorphous state by heating and cooling and the phase change material exhibits a different resistance value depending on its phase state.
- a memory device configured to store information using such a phase change material (variable resistance element) is called a phase change memory device.
- the phase state of the variable resistance element is changed by controlling the magnitude and duration of current supplied to the variable resistance element to heat and cool it.
- Information can be stored as a phase state of the variable resistance element and can be read as a resistance value thereof.
- a related phase change memory device comprises a memory cell array having a plurality of memory cells arranged in rows and columns and each using a phase change material as a variable resistance element, and a write driver connected to the memory cell array through a bit line selection circuit.
- a phase change memory device is described in, for example, Japanese Unexamined Patent Application Publication (JP-A) No. 2007-87568 (Patent Document 1).
- Patent Document 1 achieves a reduction in program time (i.e. speed-up) by reducing the setup time of a pump circuit serving to enhance the current supply capability of the write driver.
- phase change memory device for use therein is required to be further speeded up.
- the present inventors have discovered that when driving a bit line, it takes time to raise the voltage of the bit line to a predetermined value due to a relatively large capacitance of the bit line, thus resulting in a long write time.
- a semiconductor device which includes a write amplifier adapted to drive a bit line, connected to a selected phase change memory cell, with a first current driving capability and then to drive the bit line to a write voltage, corresponding to data to be written, with a second current driving capability lower than the first current driving capability.
- a write amplifier adapted to drive a bit line, connected to a selected phase change memory cell, with a first current driving capability and then to drive the bit line to a write voltage, corresponding to data to be written, with a second current driving capability lower than the first current driving capability, it is possible to quickly drive the bit line to the required voltage and thus to shorten the write time for the selected memory cell.
- FIG. 1 is a circuit diagram showing a main portion of a phase change memory device according to a first embodiment of this invention
- FIG. 2 is a time chart for explaining the operation of the phase change memory device of FIG. 1 ;
- FIG. 3 is a waveform diagram showing time-dependent changes in voltage and current at the time of driving a bit line in the phase change memory device of FIG. 1 ;
- FIG. 4 is a circuit diagram showing a main portion of a phase change memory device according to a second embodiment of this invention.
- FIG. 5 is a time chart for explaining the operation of the phase change memory device of FIG. 4 .
- FIG. 1 is a circuit diagram showing a main portion of a phase change memory device (or a semiconductor device) according to a first embodiment of this invention.
- FIG. 1 only illustrates a single memory cell 11 and a portion relating to a write operation for this memory cell 11 .
- the phase change memory device includes a plurality of memory cells arranged in rows and columns.
- the memory cell 11 is a selected memory cell in which data are written.
- the phase change memory device of FIG. 1 comprises a cell array (not illustrated) including the memory cell 11 , Yj switches (bit line selection switches) 13 for hierarchizing bit lines 12 of the cell array, respectively, write amplifiers (write drivers) 14 for driving the bit lines 12 selected by the Yj switches 13 , respectively, and voltage drop circuits 15 each for dropping the voltage of the corresponding bit line 12 to a low-potential side power supply VSS level.
- a “bit line” includes not only a line connecting between the memory cell 11 and the Yj switch 13 , but also a line connecting between the Yj switch 13 and the write amplifier 14 .
- the memory cell 11 comprises a variable resistance element 111 made of, for example, GST (GeSbTe: germanium.antimony.tellurium) and cell transistors (herein a pair of NMOSs (n-channel MOS transistors), which, however, may be a single NMOS if it has a predetermined current performance) 112 .
- GST GeSbTe: germanium.antimony.tellurium
- NMOSs n-channel MOS transistors
- the Yj switch 13 comprises a pair of an NMOS 131 and a PMOS (p-channel MOS transistor) 132 both connected to the bit line 12 .
- the write amplifier 14 comprises a first write amplifier section 141 and a second write amplifier section 142 adapted to jointly provide a first current driving capability.
- the second write amplifier section 142 provides a second current driving capability lower than the first current driving capability in a state where the first write amplifier section 141 stops driving the bit line 12 .
- the first write amplifier section 141 serves as a write amplifier for high-speed bit line activation.
- the first write amplifier section 141 comprises a PMOS 1411 with its drain and gate commonly connected to the bit line 12 , a PMOS 1412 connected between the PMOS 1411 and a high-potential side power supply VPS, and a PMOS 1413 connected between the PMOS 1411 and a high-potential side (boost) power supply VPP.
- the PMOSs 1412 and 1413 each correspond to a first switch and the PMOS 1411 corresponds to a first current trimming portion.
- a SET signal (SET pulse) and a RESET signal (RESET pulse) are input to the gates of the PMOSs 1412 and 1413 , respectively.
- the SET signal is an input signal for changing the variable resistance element 111 into a crystalline state (set state), i.e. a SET write signal
- the RESET signal is an input signal for changing the variable resistance element 111 into an amorphous state (reset state), i.e. a RESET write signal.
- the PMOSs 1412 and 1413 are turned on when the SET signal and the RESET signal are at an inactive level, respectively, and are turned off when the SET signal and the RESET signal are at an active level, respectively. It never happens that the SET signal and the RESET signal are simultaneously set to the inactive level.
- the pulse width of the SET signal is set to be greater than that of the RESET signal.
- the PMOS 1411 supplies current to the bit line 12 when either one of the PMOSs 1412 and 1413 is on and further the voltage of the
- the second write amplifier section 142 constantly supplies current to the bit line 12 so that the bit line 12 is driven with the first current driving capability higher than the second current driving capability possessed by the second write amplifier section 142 .
- the bit line 12 is driven only by the second write amplifier section 142 with its second current driving capability lower than the first current driving capability.
- the second write amplifier section 142 comprises a SET write amplifier section 142 a and a RESET write amplifier section 142 b.
- the SET write amplifier section 142 a and the RESET write amplifier section 142 b may have different current driving capabilities. However, since these amplifier sections 142 a and 142 b do not simultaneously drive the bit line 12 (the SET signal and the RESET signal are not simultaneously set to the inactive level), it is expressed in this specification that each of them has the second current driving capability.
- the SET write amplifier section 142 a comprises a switching PMOS 1421 and a current trimming PMOS 1422 connected in series between the bit line 12 and the high-potential side power supply VPS.
- the RESET write amplifier section 142 b comprises a switching PMOS 1423 and a current trimming PMOS 1424 connected in series between the bit line 12 and the high-potential side (boost) power supply VPP.
- the switching PMOSs 1421 and 1423 each correspond to a second switch and the current trimming PMOSs 1422 and 1424 each correspond to a second current trimming portion.
- the SET signal and the RESET signal are input to the gates of the switching PMOSs 1421 and 1423 , respectively.
- the PMOSs 1421 and 1423 are turned on when the SET signal and the RESET signal are at the inactive level, respectively, and are turned off when the SET signal and the RESET signal are at the active level, respectively.
- Constant voltages VWEREF 1 and VWEREF 2 are input to the gates of the current trimming PMOSs 1422 and 1424 , respectively.
- the constant voltages VWEREF 1 and VWEREF 2 are determined so that the appropriate (i.e. the second) current driving capabilities are obtained for SET writing and RESET writing, respectively.
- the current driving capability is set to be smaller for SET writing than for RESET writing.
- the voltage drop circuit 15 comprises a coincidence circuit 151 and an NMOS 152 .
- the write amplifier 14 stops supplying the current to the bit line 12 and, simultaneously, the NMOS 152 of the voltage drop circuit 15 is turned on.
- the write current is supplied to the variable resistance element 111 for a time corresponding to the pulse width of the Write pulse (i.e. the SET signal stcl or the RESET signal rstcl).
- the variable resistance element 111 is heated according to the magnitude of the supplied current and then cooled (heat dissipation) so that the phase state thereof is determined.
- the second write amplifier section 142 drives the bit line 12 with the second current driving capability determined by VWEREF 1 (or VWEREF 2 ).
- the first write amplifier section 141 when the SET signal stcl (or the RESET signal rstcl) is changed to the inactive level, the PMOS 1412 (or 1413 ) is turned on in response thereto. In this event, since the voltage of the bit line 12 is relative low (0V in the initial state), the PMOS 1411 allows current from the PMOS 1412 (or 1413 ) toward the bit line 12 to pass therethrough. That is, the first write amplifier section 141 drives the bit line 12 jointly with the second write amplifier section 142 . As a result, the bit line 12 is driven with the first current driving capability higher than the second current driving capability possessed by the second write amplifier section 142 . Thus, the rise of the voltage of the bit line 12 becomes steep to make it possible to shorten the write time for the memory cell 11 .
- VPS-Vth a voltage lower than VPS by Vth
- VPP-Vth a voltage lower than VPP by Vth
- the driving of the bit line 12 with the second current driving capability using the second write amplifier section 142 is carried out until the voltage of the bit line 12 reaches a voltage (VPS or VPP) corresponding to data to be written, and is further continued thereafter. After the voltage of the bit line 12 reaches the voltage corresponding to the data to be written, a constant current is supplied to the memory cell 11 through the bit line 12 .
- a voltage VPS or VPP
- FIG. 3 shows, in solid lines, changes in bit line voltage and current at the time of SET writing and RESET writing in the phase change memory device according to this embodiment and further shows, in broken lines, those in the related phase change memory device.
- the voltage rise at the time of driving the bit line 12 is steep.
- phase change memory device (or a semiconductor device) according to a second embodiment of this invention will be described.
- the phase change memory device of FIG. 4 differs from that of FIG. 1 in that a write amplifier 41 is used instead of the write amplifier 14 .
- the write amplifier 41 comprises a SET write amplifier section 41 a and a RESET write amplifier section 41 b.
- the SET write amplifier section 41 a has a switching PMOS 411 and a current trimming PMOS 412 connected in series between a bit line 12 and a high-potential side power supply VPS. Further, the SET write amplifier section 41 a has a control voltage changing section 413 for controlling the control voltage of the current trimming PMOS 412 .
- the control voltage changing section 413 comprises a delay circuit 4131 , and a PMOS 4132 and an NMOS 4133 each adapted to be turned on or off according to an output from the delay circuit 4131 .
- a SET signal stcl is input, as an input signal, to the gate of the switching PMOS 411 and is also input to the delay circuit 4131 . Further, a constant voltage VWEREF 1 is input to the drain of the PMOS 4132 .
- the RESET write amplifier section 41 b is configured in the same manner as the SET write amplifier section 41 a . That is, the RESET write amplifier section 41 b comprises a switching PMOS 414 and a current trimming PMOS 415 connected in series between the bit line 12 and a high-potential side (boost) power supply VPP, and a control voltage changing section 416 .
- the control voltage changing section 416 comprises a delay circuit 4161 , a PMOS 4162 , and an NMOS 4163 .
- a RESET signal rstcl is input, as an input signal, to the gate of the PMOS 414 and is also input to the delay circuit 4161 . Further, a constant voltage VWEREF 2 is input to the drain of the PMOS 4162 .
- the delay circuit 4131 (or 4161 ) supplies a delay Write pulse, obtained by delaying the Write pulse by a fixed time At, to the gates of the PMOS 4132 and the NMOS 4133 (or the PMOS 4162 and the NMOS 4163 ). Accordingly, the PMOS 4132 (or 4162 ) remains off and the NMOS 4133 (or 4163 ) remains on until the lapse of ⁇ t from a time point when the Write pulse is changed to the inactive level. In this manner, the PMOS 4132 and the NMOS 4133 (or the PMOS 4162 and the NMOS 4163 ) serve as a switching portion.
- FIG. 5 shows, in broken line, a change in bit line voltage when the constant voltage VWEREF 1 (or VWEREF 2 ) is applied to the gate of the PMOS 412 (or 415 ).
- the delay Write pulse is changed to an inactive level so that the PMOS 4132 (or 4162 ) is turned on and the NMOS 4133 (or 4163 ) is turned off.
- the constant voltage VWEREF 1 (or VWEREF 2 ) is applied to the gate of the PMOS 412 (or 415 ) so that the amount of current supplied to the bit line 12 is limited to a predetermined value or less.
- the bit line 12 is driven with a second current driving capability lower than the first current driving capability. The driving of the bit line 12 with the second current driving capability is carried out until the voltage of the bit line 12 reaches a voltage corresponding to data to be written, and is further continued thereafter.
- control voltage changing sections 413 and 416 each serve as current driving capability changing section for changing the current driving capability of the write amplifier 41 by changing the gate voltage (control voltage) of the current trimming PMOS 412 or 415 .
- phase change memory device by changing the control voltage of the current trimming PMOS 412 or 415 to change the current limit value (current driving capability), it is possible to drive the bit line with the first current driving capability higher than the second current driving capability immediately after the start of driving the bit line and to drive the bit line with the second current driving capability lower than the first current driving capability after the lapse of the fixed time. This makes it possible to shorten the write time and to prevent an increase in power consumption and the occurrence of a write error.
- the drains of the NMOSs 4133 and 4163 are each connected to the low-potential side power supply VSS in the phase change memory device of FIG. 4 , but a lower voltage (negative voltage) may be applied thereto to further enhance the current driving capability.
Abstract
A write amplifier for driving a bit line connected to a selected phase change memory cell drives the bit line with a first current driving capability and then drives the bit line with a second current driving capability lower than the first current driving capability.
Description
- This Application is a Continuation Application of U.S. patent application Ser. No. 12/591,295, filed on Nov. 16, 2009.
- This application is based on and claims priority from Japanese Patent Application No. 2008-296848 filed on Nov. 20, 2008. The disclosure thereof is incorporated herein by reference in its entirety.
- 1. Field of the Invention
- This invention relates to a memory device and a writing method thereof.
- 2. Description of the Related Art
- The phase state of a phase change material such as chalcogenide can be changed between a crystalline state and an amorphous state by heating and cooling and the phase change material exhibits a different resistance value depending on its phase state. A memory device configured to store information using such a phase change material (variable resistance element) is called a phase change memory device.
- In the phase change memory device, the phase state of the variable resistance element is changed by controlling the magnitude and duration of current supplied to the variable resistance element to heat and cool it. Information can be stored as a phase state of the variable resistance element and can be read as a resistance value thereof.
- A related phase change memory device comprises a memory cell array having a plurality of memory cells arranged in rows and columns and each using a phase change material as a variable resistance element, and a write driver connected to the memory cell array through a bit line selection circuit. Such a phase change memory device is described in, for example, Japanese Unexamined Patent Application Publication (JP-A) No. 2007-87568 (Patent Document 1).
- The technique described in
Patent Document 1 achieves a reduction in program time (i.e. speed-up) by reducing the setup time of a pump circuit serving to enhance the current supply capability of the write driver. - Following the speed-up of a computer system, however, a phase change memory device for use therein is required to be further speeded up. The present inventors have discovered that when driving a bit line, it takes time to raise the voltage of the bit line to a predetermined value due to a relatively large capacitance of the bit line, thus resulting in a long write time.
- In one embodiment, there is provided a semiconductor device which includes a write amplifier adapted to drive a bit line, connected to a selected phase change memory cell, with a first current driving capability and then to drive the bit line to a write voltage, corresponding to data to be written, with a second current driving capability lower than the first current driving capability.
- According to this invention, by providing a write amplifier adapted to drive a bit line, connected to a selected phase change memory cell, with a first current driving capability and then to drive the bit line to a write voltage, corresponding to data to be written, with a second current driving capability lower than the first current driving capability, it is possible to quickly drive the bit line to the required voltage and thus to shorten the write time for the selected memory cell.
- The above features and advantages of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which:
-
FIG. 1 is a circuit diagram showing a main portion of a phase change memory device according to a first embodiment of this invention; -
FIG. 2 is a time chart for explaining the operation of the phase change memory device ofFIG. 1 ; -
FIG. 3 is a waveform diagram showing time-dependent changes in voltage and current at the time of driving a bit line in the phase change memory device ofFIG. 1 ; -
FIG. 4 is a circuit diagram showing a main portion of a phase change memory device according to a second embodiment of this invention; and -
FIG. 5 is a time chart for explaining the operation of the phase change memory device ofFIG. 4 . - The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposes.
-
FIG. 1 is a circuit diagram showing a main portion of a phase change memory device (or a semiconductor device) according to a first embodiment of this invention.FIG. 1 only illustrates asingle memory cell 11 and a portion relating to a write operation for thismemory cell 11. Actually, the phase change memory device includes a plurality of memory cells arranged in rows and columns. Hereinafter, it is assumed that thememory cell 11 is a selected memory cell in which data are written. - The phase change memory device of
FIG. 1 comprises a cell array (not illustrated) including thememory cell 11, Yj switches (bit line selection switches) 13 for hierarchizingbit lines 12 of the cell array, respectively, write amplifiers (write drivers) 14 for driving thebit lines 12 selected by theYj switches 13, respectively, andvoltage drop circuits 15 each for dropping the voltage of thecorresponding bit line 12 to a low-potential side power supply VSS level. In this specification, a “bit line” includes not only a line connecting between thememory cell 11 and theYj switch 13, but also a line connecting between theYj switch 13 and thewrite amplifier 14. - The
memory cell 11 comprises avariable resistance element 111 made of, for example, GST (GeSbTe: germanium.antimony.tellurium) and cell transistors (herein a pair of NMOSs (n-channel MOS transistors), which, however, may be a single NMOS if it has a predetermined current performance) 112. - The
Yj switch 13 comprises a pair of anNMOS 131 and a PMOS (p-channel MOS transistor) 132 both connected to thebit line 12. - The
write amplifier 14 comprises a firstwrite amplifier section 141 and a secondwrite amplifier section 142 adapted to jointly provide a first current driving capability. The secondwrite amplifier section 142 provides a second current driving capability lower than the first current driving capability in a state where the firstwrite amplifier section 141 stops driving thebit line 12. The firstwrite amplifier section 141 serves as a write amplifier for high-speed bit line activation. - The first
write amplifier section 141 comprises aPMOS 1411 with its drain and gate commonly connected to thebit line 12, aPMOS 1412 connected between thePMOS 1411 and a high-potential side power supply VPS, and aPMOS 1413 connected between thePMOS 1411 and a high-potential side (boost) power supply VPP. ThePMOSs PMOS 1411 corresponds to a first current trimming portion. - A SET signal (SET pulse) and a RESET signal (RESET pulse) are input to the gates of the
PMOSs variable resistance element 111 into a crystalline state (set state), i.e. a SET write signal, and the RESET signal is an input signal for changing thevariable resistance element 111 into an amorphous state (reset state), i.e. a RESET write signal. ThePMOSs bit line 12 when either one of thePMOSs bit line 12 is relatively low. - As will be described later, while the first
write amplifier section 141 supplies the current to thebit line 12, the secondwrite amplifier section 142 constantly supplies current to thebit line 12 so that thebit line 12 is driven with the first current driving capability higher than the second current driving capability possessed by the secondwrite amplifier section 142. When the current supply from the firstwrite amplifier section 141 is stopped, thebit line 12 is driven only by the secondwrite amplifier section 142 with its second current driving capability lower than the first current driving capability. - The second
write amplifier section 142 comprises a SETwrite amplifier section 142 a and a RESET writeamplifier section 142 b. The SET writeamplifier section 142 a and the RESET writeamplifier section 142 b may have different current driving capabilities. However, since theseamplifier sections - The SET
write amplifier section 142 a comprises a switchingPMOS 1421 and a current trimmingPMOS 1422 connected in series between thebit line 12 and the high-potential side power supply VPS. Likewise, the RESETwrite amplifier section 142 b comprises a switchingPMOS 1423 and a current trimmingPMOS 1424 connected in series between thebit line 12 and the high-potential side (boost) power supply VPP. The switchingPMOSs PMOSs - The SET signal and the RESET signal are input to the gates of the switching
PMOSs PMOSs PMOSs - Constant voltages VWEREF1 and VWEREF2 are input to the gates of the current trimming
PMOSs - The
voltage drop circuit 15 comprises acoincidence circuit 151 and anNMOS 152. - Referring now also to a waveform diagram of
FIG. 2 , the write operation of the phase change memory device ofFIG. 1 will be described. - When a word line drive signal (SW) and a Yj selection signal (Yj) are changed to an active level at timing Act, the
cell transistors 112 and theYj switch 13 are both turned on. In the initial state, theNMOS 152 of thevoltage drop circuit 15 is on so that thebit line 12 is at the same potential as the low-potential side power supply VSS (=0V). - Then, when a Write pulse (SET signal stcl or RESET signal rstcl) is changed to an inactive level at timing Write, the
write amplifier 14 starts supplying write current and, simultaneously, theNMOS 152 of thevoltage drop circuit 15 is turned off. Thus, the voltage of thebit line 12 rises to a predetermined value. - Thereafter, when the Write pulse (stcl or rstcl) is changed to an active level, the
write amplifier 14 stops supplying the current to thebit line 12 and, simultaneously, theNMOS 152 of thevoltage drop circuit 15 is turned on. Thus, the voltage of thebit line 12 becomes equal to the low-potential side power supply voltage (=0V). - In the manner described above, the write current is supplied to the
variable resistance element 111 for a time corresponding to the pulse width of the Write pulse (i.e. the SET signal stcl or the RESET signal rstcl). Thevariable resistance element 111 is heated according to the magnitude of the supplied current and then cooled (heat dissipation) so that the phase state thereof is determined. - Now, the operation of the
write amplifier 14 will be described in further detail. - In the SET
write amplifier section 142 a (or the RESETwrite amplifier section 142 b) of the secondwrite amplifier section 142, when the SET signal stcl (or the RESET signal rstcl) is changed to the inactive level, the PMOS 1421 (or 1423) is turned on in response thereto. Thus, the secondwrite amplifier section 142 drives thebit line 12 with the second current driving capability determined by VWEREF1 (or VWEREF2). - On the other hand, in the first
write amplifier section 141, when the SET signal stcl (or the RESET signal rstcl) is changed to the inactive level, the PMOS 1412 (or 1413) is turned on in response thereto. In this event, since the voltage of thebit line 12 is relative low (0V in the initial state), thePMOS 1411 allows current from the PMOS 1412 (or 1413) toward thebit line 12 to pass therethrough. That is, the firstwrite amplifier section 141 drives thebit line 12 jointly with the secondwrite amplifier section 142. As a result, thebit line 12 is driven with the first current driving capability higher than the second current driving capability possessed by the secondwrite amplifier section 142. Thus, the rise of the voltage of thebit line 12 becomes steep to make it possible to shorten the write time for thememory cell 11. - Thereafter, when the voltage of the
bit line 12 reaches VPS-Vth (a voltage lower than VPS by Vth) (or VPP-Vth, i.e., a voltage lower than VPP by Vth), almost no current flows through thePMOS 1411. That is, the current supply to thebit line 12 from the firstwrite amplifier section 141 is stopped. On the other hand, the current supply to the bit line 12 (i.e. the memory cell 11) from the secondwrite amplifier section 142 is continued. This prevents an increase in power consumption and a write error due to supplying an amount of current more than necessary. - The driving of the
bit line 12 with the second current driving capability using the secondwrite amplifier section 142 is carried out until the voltage of thebit line 12 reaches a voltage (VPS or VPP) corresponding to data to be written, and is further continued thereafter. After the voltage of thebit line 12 reaches the voltage corresponding to the data to be written, a constant current is supplied to thememory cell 11 through thebit line 12. -
FIG. 3 shows, in solid lines, changes in bit line voltage and current at the time of SET writing and RESET writing in the phase change memory device according to this embodiment and further shows, in broken lines, those in the related phase change memory device. As clear fromFIG. 3 , in the phase change memory device according to this embodiment, the voltage rise at the time of driving thebit line 12 is steep. - As described above, according to this embodiment, it is possible to shorten the write time for the
memory cell 11 by, when driving thebit line 12, starting to drive thebit line 12 with the first current driving capability higher than the second current driving capability necessary for SET writing or RESET writing, then driving thebit line 12 with the second current driving capability lower than the first current driving capability. - Referring now to
FIG. 4 , a phase change memory device (or a semiconductor device) according to a second embodiment of this invention will be described. - The phase change memory device of
FIG. 4 differs from that ofFIG. 1 in that awrite amplifier 41 is used instead of thewrite amplifier 14. - The
write amplifier 41 comprises a SETwrite amplifier section 41 a and a RESETwrite amplifier section 41 b. - The SET
write amplifier section 41 a has aswitching PMOS 411 and acurrent trimming PMOS 412 connected in series between abit line 12 and a high-potential side power supply VPS. Further, the SETwrite amplifier section 41 a has a control voltage changing section 413 for controlling the control voltage of thecurrent trimming PMOS 412. The control voltage changing section 413 comprises adelay circuit 4131, and aPMOS 4132 and anNMOS 4133 each adapted to be turned on or off according to an output from thedelay circuit 4131. - A SET signal stcl is input, as an input signal, to the gate of the switching
PMOS 411 and is also input to thedelay circuit 4131. Further, a constant voltage VWEREF1 is input to the drain of thePMOS 4132. - The RESET
write amplifier section 41 b is configured in the same manner as the SETwrite amplifier section 41 a. That is, the RESETwrite amplifier section 41 b comprises aswitching PMOS 414 and acurrent trimming PMOS 415 connected in series between thebit line 12 and a high-potential side (boost) power supply VPP, and a controlvoltage changing section 416. The controlvoltage changing section 416 comprises adelay circuit 4161, aPMOS 4162, and anNMOS 4163. - A RESET signal rstcl is input, as an input signal, to the gate of the
PMOS 414 and is also input to thedelay circuit 4161. Further, a constant voltage VWEREF2 is input to the drain of thePMOS 4162. - Hereinbelow, referring also to
FIG. 5 , the operation of the phase change memory device ofFIG. 4 will be described. - When a word line drive signal (SW) and a Yj selection signal (Yj) are changed to an active level at timing Act,
cell transistors 112 and aYj switch 13 are both turned on. - Then, when a Write pulse (SET signal stcl or RESET signal rstcl) is changed to an inactive level at timing Write, the PMOS 411 (or 414) serving as a switch is turned on so that the
bit line 12 is driven. - In this event, the delay circuit 4131 (or 4161) supplies a delay Write pulse, obtained by delaying the Write pulse by a fixed time At, to the gates of the
PMOS 4132 and the NMOS 4133 (or thePMOS 4162 and the NMOS 4163). Accordingly, the PMOS 4132 (or 4162) remains off and the NMOS 4133 (or 4163) remains on until the lapse of Δt from a time point when the Write pulse is changed to the inactive level. In this manner, thePMOS 4132 and the NMOS 4133 (or thePMOS 4162 and the NMOS 4163) serve as a switching portion. As a result, a low-potential side voltage VSS is applied to the gate of the PMOS 412 (or 415). In this manner, the voltage VSS lower than the constant voltage VWEREF1 (or VWEREF2) is applied to the gate of the PMOS 412 (or 415) serving as a current trimming portion. Consequently, the on-state resistance of the PMOS 412 (or 415) is reduced so that the current supplied to thebit line 12 becomes large. That is, thebit line 12 is driven with a relatively high first current driving capability. As a result, the voltage rise of thebit line 12 becomes steep (high speed).FIG. 5 shows, in broken line, a change in bit line voltage when the constant voltage VWEREF1 (or VWEREF2) is applied to the gate of the PMOS 412 (or 415). - After the lapse of the fixed time At, the delay Write pulse is changed to an inactive level so that the PMOS 4132 (or 4162) is turned on and the NMOS 4133 (or 4163) is turned off. Thus, the constant voltage VWEREF1 (or VWEREF2) is applied to the gate of the PMOS 412 (or 415) so that the amount of current supplied to the
bit line 12 is limited to a predetermined value or less. As a result, thebit line 12 is driven with a second current driving capability lower than the first current driving capability. The driving of thebit line 12 with the second current driving capability is carried out until the voltage of thebit line 12 reaches a voltage corresponding to data to be written, and is further continued thereafter. - As described above, in this embodiment, the control
voltage changing sections 413 and 416 each serve as current driving capability changing section for changing the current driving capability of thewrite amplifier 41 by changing the gate voltage (control voltage) of thecurrent trimming PMOS - In the phase change memory device according to this embodiment, by changing the control voltage of the
current trimming PMOS - It is apparent that the present invention is not limited to the above embodiments, but may be modified and changed without departing from the scope and spirit of the invention.
- For example, the drains of the
NMOSs FIG. 4 , but a lower voltage (negative voltage) may be applied thereto to further enhance the current driving capability.
Claims (1)
1. A semiconductor device comprising a write amplifier adapted to drive a bit line, connected to a selected phase change memory cell, with a first current driving capability and then to drive said bit line to a write voltage, corresponding to data to be written, with a second current driving capability lower than said first current driving capability.
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US14/096,091 US20140092679A1 (en) | 2008-11-20 | 2013-12-04 | Memory device and writing method thereof |
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JP2008296848A JP2010123209A (en) | 2008-11-20 | 2008-11-20 | Memory device and method for writing the same |
JP2008-296848 | 2008-11-20 | ||
US12/591,295 US8605494B2 (en) | 2008-11-20 | 2009-11-16 | Memory device and writing method thereof |
US14/096,091 US20140092679A1 (en) | 2008-11-20 | 2013-12-04 | Memory device and writing method thereof |
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US12/591,295 Continuation US8605494B2 (en) | 2008-11-20 | 2009-11-16 | Memory device and writing method thereof |
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US14/096,091 Abandoned US20140092679A1 (en) | 2008-11-20 | 2013-12-04 | Memory device and writing method thereof |
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JP5736988B2 (en) * | 2011-06-14 | 2015-06-17 | ソニー株式会社 | Resistance change type memory device and operation method thereof |
KR101866293B1 (en) | 2011-08-23 | 2018-06-14 | 삼성전자주식회사 | Circuit for generating write signal, variable resistance memory device, and method for operating the device |
CN104025198B (en) * | 2011-12-30 | 2017-06-13 | 英特尔公司 | Phase transition storage and switch(PCMS)Wrongly write error detection |
JP2013191256A (en) * | 2012-03-14 | 2013-09-26 | Elpida Memory Inc | Semiconductor device |
CN108630249B (en) | 2017-03-24 | 2022-03-04 | 铠侠股份有限公司 | Semiconductor memory device with a plurality of memory cells |
KR20190042892A (en) * | 2017-10-17 | 2019-04-25 | 에스케이하이닉스 주식회사 | Semiconductor memory apparatus and operating method thereof |
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US20100124104A1 (en) | 2010-05-20 |
US8605494B2 (en) | 2013-12-10 |
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