WO2001079924A1

WO2001079924A1 - Integrated lcd display and electroluminescent module

Info

Publication number: WO2001079924A1
Application number: PCT/US2001/011813
Authority: WO
Inventors: Robert Stinauer; Benjamin Rush
Original assignee: Motorola Inc., A Corporation Of The State Of Delaware
Priority date: 2000-04-14
Filing date: 2001-04-11
Publication date: 2001-10-25
Also published as: AU2001253369A1

Abstract

An integrated module (10) including a liquid crystal display (LCD) module (16) and an electroluminescent (EL) module (18) is provided. A polarizer layer (30) is disposed between the two modules and functions as both a polarizer for the LCD module (16) and an insulating substrate layer for a conductive layer (64) of the EL module (18). The integrated module (10) comprising the LCD module, EL module, and integrated polarizer layer may be used in cellular telephones (12) and personal data assistants (PDAs) (14).

Description

INTEGRATED LCD DISPLAY AND ELECTROLUMINESCENT MODULE

Field of the Invention

The present invention relates generally to display devices that use electroluminescent modules and, more particularly, to a liquid crystal display device having an integrated a liquid crystal display module and an electroluminescent backlight module.

Background of the Invention

Liquid crystal display (LCD) devices are used in cellular telephones, personal data assistants (PDAs) , portable computers, and other applications to display information. One reason for the popularity of LCDs as a display is their relatively small size in comparison to traditional display devices, such as cathode ray tubes. Commonly utilizing a matrix of thin-film transistor switching elements that are each responsive to a relatively small voltage, LCD displays can be made substantially thin, lightweight, and, thus, portable. These LCD devices may include a LCD module and an electroluminescent (EL) module. As is well known in the art, LCD modules use a birefringent liquid crystal material which alters the polarization state of an incident light wave. This liquid crystal material is housed between two linear polarizers oriented such that their respective axes of polarization are parallel to one another. With this orientation, the light wave, which enters the liquid crystal linearly polarized along one axis is rotated into an orthogonal polarization after passing through the liquid crystal. This orthogonally polarized wave will be blocked by the linear polarizer on the exit end of the liquid crystal. To selectably transmit some of the light traveling through the liquid crystal, numerous types of switching elements may be used with LCD modules, all elements sharing substantially the same purpose, i.e., establishing an electric field across a portion of the liquid crystal such that the liquid crystal material does not alter the polarization state of the incident light wave as the light wave travels through the crystal. The liquid crystal housing, front polarizer, and rear polarizer apparatus is oriented to pass light through the LCD under this electric field biasing. Such a LCD module is well known in the art.

To provide a light source for the LCD module and to enhance the visibility of a LCD device during operation in environments with little or no ambient light, LCD modules are operated with a backlighting source, such as an electroluminescent (EL) module. EL modules have an electroluminescence phosphor layer of material that will luminesce upon excitation by electron movement across and absorption within the layer. To create such luminescence, EL modules comprise a planar sandwich structure, in which two conductor layers are used, one on each side of the electroluminescence layer, to establish a current forming path across the electroluminescence layer. These two conductor layers are typically thin layer films made of conductive material . One conductor layer can be placed onto a base layer that serves as the bottom of the EL module. Similarly, the other (i.e., upper), conductor layer may be placed on the other side of the electroluminescence layer except that the upper conductor layer must be substantially optically transparent so that luminescence from the electroluminescence layer is transmitted to the LCD module. Therefore the upper contact is usually a thin layer of conductive material deposited onto a thin insulating film. In addition to providing a substrate for an upper contact, the insulating film acts as a protective upper surface of the EL module package, thus allowing the package to be handled, tested, and placed in different environments of use without damaging the conductor layers or contaminating the electroluminescence layer of the EL module. Furthermore, a dielectric layer is often used between the electroluminescence layer and one of the conductor layers to electrically isolate the two conductor layers from shorting together. Thus, the EL module generally forms an electrode-dielectric- electroluminescence layer-electrode-insulating film multilayer sandwich. This multilayer sandwich, i.e., EL module, is attached to the rear polarizer of the LCD module, by adhesively laminating the insulating film of the EL module to the rear polarizer of the LCD module, thus forming an entire LCD device.

Though this implementation of a separate EL module with a separate LCD module is known, it produces a number of undesirable results in the particular environments of use listed above. First, it is always desirable in applications such as portable cellular telephones or PDAs to reduce display thickness and weight. Both of these directly effect profitability. Second, it has been desirable to reduce the noise created by affixing two separate modules. Vibrational noise, is particularly problematic in cellular telephone applications where signal fidelity for reception and transmission purposes is very important. Unfortunately, vibrational noise is an inherent characteristic of two module devices, such as LCD devices. In effect, the LCD module being driven by one current source and the EL module being driven by another current source produce a vibrational noise similar to a small piezo-electric speaker when operated in contact with one another .

Moreover, both of these disadvantages of the state of the art are magnified in many currently desirable applications in which a touchscreen, which adds thickness and weight to an LCD and EL module combination, is used on the upper surface of the LCD to allow a user to interact with the device by depressing different portions of the touchscreen in response to information displayed on the LCD display. In these applications, it is further desirable to reduce device thickness because of the added touchscreen layers .

Thus there is a need for an improved LCD module and backlighting EL module which has a reduced thickness in comparison to the prior art and which reduces vibration and noise between the two modules.

Brief Description of the Drawings

FIG. 1 is an isometric view of the integrated LCD module and EL module of an embodiment of the present invention.

FIG. 2 is a top plan view of a cellular telephone in which the integrated LCD module and EL module of FIG. 1 is used.

FIG. 3 is a top plan view of a PDA in which the integrated LCD module and EL module of FIG. 1 is used.

FIG. 4 is an isometric view of an alternative embodiment of the integrated LCD module and EL module. FIG. 5 is an isometric view of the bottom surface of an integrated rear polarizer in accordance with an aspect of the present invention.

FIG. 6 is a plan view of a bottom insulating layer of the embodiment of FIG. 4. Detailed Description of the Preferred Embodiments

As exemplified in the present description of a preferred embodiment, a LCD and integrated EL module

(hereinafter referenced as "the integrated module 10") is shown preassembled in a perspective view in Fig. 1. As will be apparent from the following description, the integrated module offers improvements over the disadvantages discussed above, in that it requires less layers than the state of the art and reduces the vibrational noise associated therewith. As such, the integrated module may be used in lieu of the state of the art LCD and EL modules in numerous applications, including cellular telephones 12, as shown in Fig. 2, and PDAs 14, as shown in Fig. 3. It will be readily appreciated by persons of ordinary skill in the art that the preferred embodiments may be employed in other applications as well.

With reference to Fig. 1, the integrated module comprises an LCD module 16 integrated with an EL module 18. The modules 16,18 are individually referenced for ease of comprehension and together form the integrated module 10. The LCD module 16 comprises a front polarizer 20 and a liquid crystal housing 22 with two LCD glass panels 24, 26 all of which are rectangular in shape in a planar view.

Though not an aspect of the present invention and therefore not shown, it is known that each glass panel 24, 26 can have an indentation so that when the two glass panels 24, 26 are brought into contact the indentations define a space into which a liquid crystal material may be hermetically sealed. The rear polarizer traditionally found in LCD modules has been replaced by an integrated rear polarizer 30 that is shared by both the LCD module 16 and the EL module 18. The front polarizer 20 and the integrated rear polarizer 30 are linear polarizers with their respective axes of polarization oriented in parallel. The front polarizer 20 is sized to cover the entire upper surface of the liquid crystal housing 22, or at least that functional area of the housing 22 that will be visible for display to and/or inking by the user. Likewise, the integrated rear polarizer 30 can cover the entire lower surface of the liquid crystal housing or its functional area.

Though none are shown, it will be appreciated by persons of ordinary skill in the art that many types of biasing means may be used to establish electric fields across the liquid crystal housing 22, including a thin optically translucent indium tin oxide (ITO) contact layer placed between the upper surface of the liquid crystal housing 22 and the front polarizer 20, as well as another thin ITO contact layer placed between the lower surface of the liquid crystal housing 22 and the rear polarizer 30. ITO layers absorb approximately 10% of the radiation incident upon them. Furthermore, as is known in the art, it may desirable to set up the upper ITO contact layer of the LCD module as a matrix of electrodes in a pixelated pattern and individually connected to external leads. This matrix pattern layer can be used to display characters, images, symbols, and the like. The cellular telephone 12 of FIG. 2 shows a LCD display 32 with a number 34 displayed on the screen using an exemplary pixelated upper electrode pattern. Similarly, the PDA 14 of FIG. 3 shows a LCD display 36 with a listing of names 38 and a menu bar 40 of symbols, which may be selected by depressing a stylus 42 onto a touchscreen over the LCD display 36. In either of these applications, the characters, images or symbols would be created by illuminating certain electrodes of the upper ITO layer of the LCD module. The integrated module 10 of FIG. 1 also comprises the EL module 18 which has numerous layers, including an electroluminescence layer 44. The electroluminescence layer 44 is preferably a phosphor layer that converts electron energy, generated by a current path across the phosphor layer, into radiant energy, i.e., visible luminescence for backlighting the LCD module. However, other suitable electroluminescence layers may be used in the present invention. And while the EL module 18 is shown in use in the integrated module 10, the EL module 18 with integrated rear polarizer 30 may exist separately from the integrated application, and still be within the scope of the present invention.

In addition to the electroluminescence layer 44, the EL module 18 includes (from bottom to top) a bottom insulating layer 48 with a rear busbar 50 and lead 52 attached thereto, a dielectric layer 54 upon which the electroluminescence layer 44 is deposited, and the integrated rear polarizer 30, each of which are rectangular in shape from a plan view and have a surface area substantially the same as the liquid crystal housing 22 or at least the functional area thereof . At the bottom of the EL module 18, the bottom insulating layer 48 is disposed to electrically isolate the EL module 18 from its environment of use, such as circuitry within the cellular telephone 12 or the PDA 14. Preferably, the bottom insulating layer is made of a polyester film of approximately 2 mil thickness to provide necessary isolation and to avoid detrimental capacitive effects. Nevertheless, one of ordinary skill in the art will recognize that other insulating materials may be used.

For providing an electric field across the electroluminescence layer 44, the rear busbar 50 and the lead 52 are disposed on the bottom insulating layer 48. The rear busbar 50 forms one electrode current path across the electroluminescence layer 44. To establish a bias for this current path across the entire rectangular surface area of the electroluminescence layer 44 and not just that portion above the rear busbar 50, a rear conductive layer 56 is used. In one embodiment, the rear conductive layer 56 is a carbon or silver conductive ink deposited, i.e., screened, onto the entire surface of the bottom insulating layer 48. In another embodiment described below and shown in FIG. 4, the carbon or silver ink can be screened onto two portions of the bottom insulating layer 48. In either embodiment, inks impregnated with other conductive materials, such as copper, may also be used, however carbon and silver impregnated inks are preferred for their reduced resistance. In addition to serving as a biasing electrode, the rear conductive layer 56 can be used to adhesively bond the rear busbar 50 to the bottom insulating layer 54. Alternatively, the rear busbar 50 can be separately bonded to the bottom insulating layer 48. Furthermore, as will be apparent to one of ordinary skill in the art from this disclosure, other types of rear conductive layers, such as thin metallic conductive layers adhesively bonded to the bottom insulating layer 48, may be used and, as such, are considered with the scope of the present invention. The lead 52 of the rear busbar 50 is connected to an AC current source 66.

Similarly, a front busbar 60 with lead 62 is connected to a front conductive layer 64 (FIG. 5) which is formed on the bottom surface of the integrated rear polarizer 30, according to the present invention. The front conductive layer 64 should be optically transparent to allow light from the EL module 18 to backlight the LCD module 16, and, thus, a layer containing ITO is used as the front conductive layer 64. Preferably, the ITO layer is formed onto the bottom of the integrated rear polarizer 30 by sputtering. A view of the bottom surface of the integrated rear polarizer 30 with a sputtered ITO layer thereon is shown in FIG. 5. The integrated rear polarizer 30 is formed of a polyester film through known means. The integrated rear polarizer 30 can be approximately 7 mils thick, for example, and because the rear polarizer 30 is used by both the LCD module 16 and the EL module 18 it functions both as an insulating film upon which the front conductive layer 64 of the EL module 18 can be deposited and as a rear polarizer for the LCD module 16. Furthermore, because the front conductive layer 64 is deposited onto the bottom of the integrated rear polarizer 30, the integrated rear polarizer 30 also electrically isolates the front conductive layer 64 from the ITO layer disposed on the bottom of the liquid crystal housing 22, discussed generally above.

Conductive layers other than an ITO layer and means of connecting these conductive layers to a rear polarizer other than sputtering may be used. For example, a thin patterned metallic layer may be adhesively bonded to the rear polarizer. By connecting an AC current source 66 to the front conductive layer 64 via the lead 52 and connecting the AC current source 66 to the rear conductive layer 56 via the lead 52, a current path is formed across the electroluminescence layer 44. This integrated rear polarizer 30 with sputtered front conductive layer 64 is advantageous over known devices, because it reduces the layers needed to form a LCD module and EL module pair by combining into one layer the rear polarizer traditionally used in LCD modules the insulating layer traditionally used in EL modules (approximately 5 mils thick) , and the adhesive laminate layer traditionally used (approximately 2.5 mils thick) to combine the two modules. Thus, with the use of this combined layer, i.e., the integrated rear polarizer 30, reductions in overall thickness of approximately 7.5 mils, or .15 mm, have been shown. In addition to this advantage, because the two modules 16, 18 are integrated in the present invention, vibrational noise between the modules will be low. By integrally mounting the two modules with the rigid rear polarizer 30 being shared by both, the liquid crystal housing 22 acts as a stiffener for the EL module 18, thus substantially attenuating the vibrational effects that occur in known non-integrated LCD and EL module devices.

The front conductive layer 64 is disposed in electrical contact with the electroluminescence layer 44 by adhesively bonding or laminating the integrated rear polarizer 30 to the electroluminescence layer 44. To electrically isolate the front conductive layer 64 from the rear conductive layer 56, the dielectric layer 54 is disposed between the electroluminescence layer 44 and the rear conductive layer 56. The dielectric layer 54 is preferably made of a barium titanate. Alternatively, the dielectric layer 54 can be located in other positions such as between the front conductive layer 64 and the electroluminescence layer 44, with the rear conductive layer 56 being electrically coupled to the electroluminescence layer 44. The dielectric layer 54 serves to electrically isolate the two conductive layers 56, 64 so that they do not short one another.

In the alternative embodiment of FIG. 4, a second integrated module 68 is shown, wherein the positioning of the layers of the EL module 18 has been slightly modified to create another EL module 69 with a first busbar 70 being located on the bottom insulating layer 48 along with a second busbar 72, both with leads 74, 76, respectively. In this embodiment, the carbon or silver ink deposited onto the bottom insulating layer 48 is not deposited over the entire area as with the previous embodiment of FIG. 1, but rather is deposited onto two isolated locations 78, 80. The large first portion 80 of the upper surface of the bottom insulating layer 48 is covered with conductive material. In this case, the large portion 80 is electrically connected to the second busbar 72 and serves as a rear conductive layer 78 (FIG. 6) . Along an edge of the bottom insulating layer 48 is deposited the narrow second portion 78 of conductive material which is electrically connected to the first busbar 70. The second portion 78 is connected to the front conductive layer 64 via an electrical connection not shown. This electrical connection can come in numerous forms, including an external wire or conductive layer extending along a path defined by a hole 82 in the dielectric layer 54 and electroluminescence layer 44. The electrical connection through the hole 82 can be formed by a conductive material, such as a carbon or silver ink layer, which is long enough to extend through the hole 82 forming an electrical contact between the front conductive layer 64 and the second conductive portion 78, but which will not short out the electroluminescence layer 44.

In operation, the integrated module 10 can be assembled and placed into the cellular telephone 12 or the PDA 14. In either case (with reference to the embodiment of FIG 1) , the leads from the rear busbar 50 and from the front busbar 60 are connected to the AC current source 66, such as an inverter circuit driven by a battery source. By way of example, depressing one of a group of keys 90 on the keypad 92 of the cellular telephone 12 may activate the current source 66 causing it to supply driving current to the front and rear busbars 50, 60. With the front and rear busbars 50, 60 connected to the front and rear conductive layers 56, 64, respectively, a current path is created through the electroluminescence layer 44 thus exciting the electroluminescence layer 44 which in turn creates a visible luminescence. A portion of the visible luminescence is partially transmitted through the front conductive layer 64 and the integrated rear polarizer 30. This partially transmitted and polarized light is thereafter incident on the liquid crystal housing 22, and thus backlights the LCD module 16. Under no electric field biasing across the liquid crystal housing 22, very little backlight from the EL module 18 is transmitted from the front polarizer 20 of the LCD module 16. However, as is readily known to persons of ordinary skill in the art, the electrodes on the LCD (not shown but described above) may be programmed to establish electric fields across certain electrodes to selectably transmit light from the LCD module 16. For example, in FIG. 2, the keys 90 associated -with the numbers "0", "1", and "3" have been pressed and the corresponding number 34 has been displayed on the LCD screen 32. Similarly with the PDA 14, if a user selects from the menu bar 40 on the LCD display 36 or uses the stylus 42 to write symbols on the PDA 14 a corresponding pixelated listing of names 38 can be displayed. The operation of the integrated module 68 operates in a similar manner to that of the integrated module 10.

Many additional changes and modifications could be made to the invention without departing from the fair scope and spirit thereof. The scope of some changes is discussed above. The scope of others will be come apparent from the appended claims.

What we claim is:

Claims

1. A liquid crystal display (LCD) with a liquid crystal housing having first and second surfaces and an integrated electroluminescent module for providing backlit visible luminescence to the LCD, comprising: a rear polarizer layer, with a front and rear surface, wherein said front surface of said rear polarizer layer is mounted on the second surface of said liquid crystal housing; a first conductive layer of said electroluminescent module operatively coupled to an excitable luminescence layer of said electroluminescent module; and a second conductive layer forming a current path with said first conductive layer across said excitable luminescence layer, wherein said second conductive layer is formed on said rear surface of said rear polarizer layer.

2. The LCD and integrated electroluminescent module of claim 1, wherein the second conductive layer consists essentially of a conductive material sputtered on said rear surface of said rear polarizer layer.

3. The LCD and integrated electroluminescent module of claim 2, wherein said conductive material consists essentially of indium tin oxide.

4. The LCD and integrated electroluminescent module of claim 1, further comprising an insulating layer between said first conductive layer and said excitable electroluminescent layer.

5. The LCD and integrated electroluminescent module of claim 4, wherein the insulating layer is a dielectric layer consisting essentially of barium titanate.

' 6. The LCD and integrated electroluminescent module of claim 1, wherein said rear polarizer layer is made of a flexible polyester film with a thickness substantially smaller than a width and a height of said rear polarizer layer.

7. The LCD and integrated electroluminescent module of claim 1, wherein said excitable luminescence layer comprises a phosphor layer.

8. The LCD and integrated electroluminescent module of claim 1, wherein said electroluminescence module further comprises : a dielectric layer disposed between said second conductive layer and said excitable luminescence layer for electrically isolating said second conductive layer from said first conductive layer; a front busbar connected to said second conductive layer; and a rear busbar connected to said first conductive layer, both said front busbar and said rear busbar being connected to a current source.

9. The LCD and integrated electroluminescence module of claim 1, wherein said first conductive layer consists essentially of a conductive ink.

10. The LCD and integrate electroluminescence module of claim 9, wherein said conductive ink is deposited onto an insulating layer operatively coupled to said electroluminescence layer.

11. The LCD and integrated electroluminescence module of claim 10, wherein said conductive ink consists essentially of silver.

12. The LCD and integrate electroluminescence module of claim 10, wherein said conductive ink consists essentially of carbon.

13. The LCD and integrated electroluminescence module of claim 1, wherein said liquid crystal housing comprises a first glass layer and a second glass layer, both layers being affixed to one another to hermetically seal a liquid crystal material therebetween.

14. The LCD and integrated electroluminescence layer of claim 13, further comprising a first conductive layer on said first glass layer and a second conductive layer on said second glass layer for producing an electrical field across said liquid crystal material to selectably transmit said visible luminescence from said electroluminescent module.

15. A portable telephone with a liquid crystal display (LCD) , with a liquid crystal housing having first and second surfaces, and an integrated electroluminescent module for providing backlit visible luminescence to the LCD, comprising: a rear polarizer layer, with front and rear surfaces, wherein said front surface of said rear polarizer is mounted to said second surface of said liquid crystal housing; a first conductive layer mounted below an excitable luminescence layer of said electroluminescent module; and an second conductive layer forming a current path with said first conductive layer across said excitable luminescence layer, wherein said second conductive layer is formed on said rear surface of said rear polarizer layer.

16. For use in displaying information, a portable data assistant (PDA) with a liquid crystal display (LCD) , with a liquid crystal housing having first and second surfaces, and an integrated electroluminescent module for providing backlit visible luminescence to the LCD, comprising: a rear polarizer layer, with front and rear surfaces, wherein said front surface of said rear polarizer is mounted to said second surface of said liquid crystal material housing; a first conductive layer mounted below an excitable luminescence layer of said electroluminescent module; and an second conductive layer forming a current path with said first conductive layer across said excitable luminescence layer, wherein said second conductive layer is formed on said rear surface of said rear polarizer layer.

17. An electroluminescence module for use in backlighting a liquid crystal display (LCD) with front and rear polarizer layers, comprising: an electroluminescence layer disposed between a first conductive layer and a second conductive layer, both conductive layers connected to a current source and forming a current path across said layer for creating a visible luminescence output in the direction of said LCD, said second conductive layer being formed on said rear polarizer layer of said LCD; and an insulating layer disposed between said second conductor layer and said electroluminescence layer.

18. The electroluminescence module of claim 17, wherein said second conductive layer consists essentially of a conductive material sputtered on said rear surface of said rear polarizer layer.

19. An electroluminescence module for use in backlighting a display device, comprising: a polarizer layer; an electroluminescence layer disposed between a first conductive layer and a second conductive layer, the first conductive layer and the second conductive layer both being connected to a current source and forming a current path across said electroluminescence layer for creating a visible luminescence output in the direction of said display device, said second conductive layer being formed on said polarizer layer; and an insulating layer between said second conductor layer and said electroluminescence layer.

20. The electroluminescence module of claim 19, wherein said display device is a liquid crystal display (LCD) device and wherein said polarizer layer is operatively coupled to a surface of said LCD device.

21. The electroluminescence module of claim 20, wherein the polarizer layer is a linear polarizer consisting essentially of a polyester film and forms a polarizing layer of said LCD device.

22. The electroluminescence module of claim 20, wherein said second conductive layer consists essentially of a conductive material sputtered on said rear surface of said rear polarizer layer.