WO2000046636A1

WO2000046636A1 - Stacked bistable, cholesteric liquid crystal display utilizing single set of drive electronics

Info

Publication number: WO2000046636A1
Application number: PCT/US1999/030103
Authority: WO
Inventors: Gene A. Miceli; Chad M. Jones; Xiao-Yang Huang
Original assignee: Kent Displays, Inc.
Priority date: 1999-02-05
Filing date: 1999-12-16
Publication date: 2000-08-10

Abstract

A stacked, passive display apparatus including first and second layers of chiral nematic liquid crystal material includes substrates (30a, 28a, 28b, 30b) binding the first layer (34a) of liquid crystal material and the second layer (34b) of liquid crystal material so as to prevent communication between the first and second layers of liquid crystal material. Electrical conductors (44) interconnect the first row electrodes (37) and the second row electrodes (38) and electrical conductors (43) interconnect the first column electrodes (39) and the second column electrodes (40). Row driver electronics (202) are electrically coupled to one of the first row electrodes (37) and the second row electrodes (38) for applying voltage to both the first row electrodes (37) and the second row electrodes (38). Column driver electronics (204) are electrically coupled to one of the first column electrodes (39) and the second column electrodes (40) for applying voltage to both the first column electrodes (39) and the second column electrodes.

Description

STACKED BISTABLE. CHOLESTERIC LIQUID CRYSTAL DISPLAY UTILIZING SINGLE SET OF DRIVE ELECTRONICS

This application was made in part with Government support under cooperative agreement number N61331-96C-0042 awarded by the Defense Advanced Research Projects

Agency (DARPA). The government has certain rights in this invention. Related Application

This application is a Continuation-in-Part of application Serial No. 08/823,329, entitled, "DISPLAY DEVICE REFLECTING VISIBLE AND INFRARED RADIATION," filed March 22, 1997. Field of the Invention

The present invention relates to a multi-layer or stacked cholesteric liquid crystal

display and, more particularly, to a stacked cholesteric liquid crystal display utilizing a single

set of drive electronics to drive a plurality of spaced apart sets of row electrodes and sets of column electrodes affixed to a plurality of stacked substrates. Background of the Invention

Typically, a liquid crystal display comprises a single layer of liquid crystal material

sandwiched between inner surfaces of generally planar substrates. On an inwardly facing

surface of one of the substrates is disposed a set or array of parallel column electrode segments (column electrode array) and on an inwardly facing surface of the other of the

substrates is a set or array of parallel row electrode segments (row electrode segments), extending generally perpendicular to the column electrode array. The row and column

electrode segments (also referred to as "row and column electrodes") are spaced apart by the

thin layer of liquid crystal material. Display picture elements or pixels are defined by regions of liquid crystal material adjacent the intersection of the row and column electrode segments.

Upon application of a suitable electric field, a pixel will assume one of two or more optical states (e.g., a reflective optical state or a non-reflective optical state). A pixel, P(xi,yj), formed at the overlapping or intersection of the ith row electrode segment and the jth column electrode segment is subject to an electric field resulting from the potential difference between a voltage applied to the ith row electrode segment and a voltage applied to the jth column electrode segment.

The optical state of an image pixel depends upon the configuration of the liquid crystal material defining the image pixel. Moreover, the state of the liquid crystal material may be changed upon imposing an appropriate electric field across the liquid crystal material for an appropriate period of time. This is accomplished by appropriately energizing the row and column electrodes defining an image pixel so as to generate an electric field having a desired

magnitude for the appropriate period of time.

Recent advances in liquid crystal material research have resulted in the discovery of

chiral nematic (also called cholesteric) liquid crystal displays. Cholesteric liquid crystal materials are able to maintain a given reflective state (reflective or nonreflective) without the

need for the constant application of an electric field. When data or an image displayed on the

liquid crystal display is to be changed, some pixels will require a change in their state of reflectance while others will not. The display driver circuitry appropriately applies the electric

field to those pixels whose reflectance states need to be changed in order to effect the desired image change. If the back of the display is painted with a black material, a pixel with a low

reflectance or nonreflective state will appear as a black area to the viewer. If the liquid crystal material has a visible color appearance in its high reflective state, a pixel in a high reflectance

state will appear to the viewer as a visible colored area in the display. Display driver circuitry is coupled to the vertical and horizontal electrodes of the row and column electrode arrays. Operating under the control of a logic and control unit, the display driver circuitry energizes the row and column electrodes with appropriate voltage waveforms such that an appropriate voltage across each pixel is generated. The voltage

across a pixel will either cause it to remain in its present state of reflectance or change its state of reflectance. The image generated by the display pixels may be modified by changing the state of selected pixels. In this way, text or image data can be presented for viewing on the display. Summary of the Invention The present invention is directed to a stacked cholesteric liquid crystal display having a

novel drive electronics configuration and electrical connections thereto. The stacked cholesteric liquid crystal display comprises a plurality of layers of spaced apart cholesteric liquid crystal material, each layer of liquid crystal material being bounded by a set of row electrodes and a set of column electrodes, the regions of liquid crystal material adjacent the intersections of the row and column electrodes defining a set of image pixels. The sets of row

electrodes and column electrodes associated with the different cholesteric liquid crystal layers

are aligned such that each set of image pixels associated with a different liquid crystal layer are

in vertical alignment (that is, in alignment as seen by a viewer looking perpendicular to the display outer surface). The alignment of sets of image pixels provides for greater brightness of

high reflectance state image pixels as seen by a viewer of the display, that is, an image pixel visible to the viewer as a single pixel is actually comprised of two (or more) aligned pixels.

The combined brightness of two aligned pixels in their high reflectance states provides for a greater brightness than the brightness of a single pixel in its high reflectance state.

The novel drive electronics of the stacked cholesteric liquid crystal display include a single set of drive electronics comprising a single set of row driver electronics and a single set of column driver electronics for energizing the multiple sets of spaced apart row electrodes and spaced apart column electrodes of the display. An electrical coupling is provided between

the plurality of sets of row electrodes and an electrical coupling is provided between the plurality of sets of column electrodes. Since the plurality of sets of row electrodes are electrically coupled, the single set of row driver electronics controls energization of all of the row electrodes in the plurality of sets of row electrodes and since the plurality of sets of column electrodes are electrically coupled, the single set of column driver electronics controls energization of all of the column electrodes in the plurality of sets of column electrodes. The sets of row and column driver electronics constitute a single set of drive electronics.

The electrical coupling between the sets of row electrodes preferably utilizes flexible interconnects. Each flexible interconnect electrically couples a spaced apart pair of sets of row electrodes or a spaced apart pair of sets of column electrodes. The flexible interconnects are preferably connected externally to the display substrate. That is, the flexible interconnects are connected in an overlying position on the corresponding indium tin oxide (ITO) traces that are

disposed on a substrate. A conductor need not pass through the substrate for electrical

connection. The row driver electronics is electrically coupled to a selected one of the sets of

row electrodes (e.g., to one substrate) and, through one or more flexible interconnects, is electrically coupled to the remaining sets of row electrodes. Also, preferably, the electrical coupling between the sets of column electrodes utilizes a flexible interconnect. The column

driver electronics is electrically coupled to a selected one of the sets of column electrodes (e.g., to one substrate).

In one aspect of the invention, a stacked display apparatus includes: first and second layers of chiral nematic liquid crystal material; substrates bounding the first layer of liquid crystal material and the second layer of liquid crystal material so as to prevent communication between the first layer of liquid crystal material and the second layer of liquid crystal material; first row and first column conductive electrodes disposed on the substrates bounding the first

liquid crystal layer and second row and second column conductive electrodes disposed on the substrates bounding the second liquid crystal layer. The first row electrodes extend transverse to and on a different substrate than the first column electrodes and the second row electrodes

extend transverse to and on a different substrate than the second column electrodes. Also included are electrical conductors interconnecting the first row electrodes and the second row electrodes and electrical conductors interconnecting the first column electrodes and the second column electrodes; row driver electronics electrically coupled to one of the first row electrodes and the second row electrodes for applying voltage to both the first row electrodes and the second row electrodes; and column driver electronics electrically coupled to one of the

first column electrodes and the second column electrodes for applying voltage to both the first

column electrodes and the second column electrodes. The stacked display apparatus of the present invention is suitable for any passive display including matrix displays and segmented displays. A matrix display is one in which

each set of row electrodes comprise a plurality of parallel substantially linear electrode

segments and each set of column electrodes comprise a plurality of substantially linear parallel

electrode segments and the column segments are substantially perpendicular to the row

segments resulting in an orthogonal array of pixels. On the other hand, a segmented display includes sets of row and column electrodes that may not be linear or parallel, an example would be a display having a series of pixels comprising a seven segment display.

In the invention disclosed in U.S. Application Serial No. 09/063,907, filed April 21,

1998, and entitled "UNIPOLAR WAVEFORM DRIVE METHOD AND APPARATUS FOR A BISTABLE LIQUID CRYSTAL DISPLAY," a method and display driver circuitry for activating a bistable, cholesteric liquid crystal display using unipolar waveforms and a pipelining scheme for addressing multiple rows of the display to provide high speed updating of the display is disclosed. U.S. application Serial No. 09/063,907 is assigned to the assignee

of the present invention and is incorporated in its entirety herein by reference. Also incorporated herein by reference in its entirety is U.S. Application Serial No. 08/823,329,

entitled, "DISPLAY DEVICE REFLECTING VISIBLE AND INFRARED RADIATION," filed March 22, 1997, also assigned to the assignee of the present invention.

These and other objects, features and advantages of the invention will become better understood from the detailed description of the preferred embodiments of the invention which are described in conjunction with the accompanying drawings.

Brief Description of the Drawings

Figure 1 is a perspective view of a stacked, bistable passive matrix, cholesteric liquid crystal display of the present invention;

Figure 2 is a sectional view of the display of Figure 1 as seen from a plane indicated by the line 2-2 in Figure 1 ;

Figure 3 is a sectional view of the display of Figure 1 as seen from a plane indicated by

the line 3-3 in Figure 1;

Figure 4 is a side elevation view of the two interconnected displays comprising the display of Figure 1 at the beginning of the assembly process;

Figure 5 is a side elevation view of the two interconnected displays of Figure 4 showing the displays being folded towards each other after electrical connection of electrodes

from each display; Figure 6 is a side elevation view of the two interconnected displays of Figure 4 showing the displays in a stacked formation;

Figure 7 is a side elevation view of the two interconnected displays after electrical connection of electrodes from each display, this view being rotated 90° from the view shown in Figure 6; and

Figure 8 is a schematic diagram of the display of Figure 1 and a block diagram representation of drive electronics connected to the display.

Detailed Description of Preferred Embodiments

Turning now to Fig. 1, the display 20 of the present invention is a stacked passive matrix, bistable, cholesteric liquid crystal display, for example, a VGA sized stacked liquid crystal display comprising 480 rows by 640 columns. This means that the display 20 comprises 307,200 image pixels (480 rows x 640 columns) and includes a plurality of spaced

apart layers of cholesteric liquid crystal material. In this preferred embodiment, there are two layers 34a, 34b (Figures 2 and 3) of cholesteric liquid crystal material. It should be appreciated that the display 20 may be used in a wide variety of devices utilizing liquid crystal

displays, such as those in which sharp contrast between the reflective and nonreflective

portions of the display is desired. For example, the display 20 may advantageously be used to

display information updated periodically such as in the case of an electronic sign. It should also be appreciated that the concepts presented herein apply to displays having three or more

spaced apart liquid crystal layers. Also, the display 20 can be fabricated in sizes other than

VGA size, for example, the display 20 of the present invention may be fabricated as an SVGA sized display of 800 rows by 600 columns of image pixels. Similarly, the display 20 could be fabricated as a 320 row by 240 column display (76,800 pixels), which is a one quarter of VGA display size. While the display 20 is a matrix display, it should be appreciated by one skilled in the art that the display could also be a segmented display. In a segmented display, the

electrodes may be fabricated in various shapes and disposed in orthogonal or non-orthogonal orientations to generate desired image configurations, for example, in a segmented liquid crystal display short segments of row and column electrodes may advantageously be disposed to create a seven segment numerical display. In other segmented displays electrode segments of irregular shape may be used to generate an icon on the display.

The bistable liquid crystal display 20 includes layers 34a, 34b comprised of cholesteric or what is known as chiral nematic liquid crystal material. Cholesteric liquid crystal material is

advantageous in that it maintains its reflective state even in the absence of an electric field.

The display 20 is a passive matrix because the horizontal (row) and vertical (column) electrode segments 37, 38, 39, 40 which define the image pixels of the display are passive circuit elements (resistors) as opposed to comprising active circuit elements such as transistors. A passive matrix display, such as the display 20, is advantageous because of lower cost compared to active matrix displays. Passive matrix displays have a much simpler design

compared to active matrix displays and are thus easier to manufacture and can be produced in

greater yields.

The display 20 includes a top display 22 and bottom display 24 (preferably, the bottom display 24 is identical in structure to the top display 22) separated by a layer of index of

refraction matching material 26 such as an adhesive, a pressure sensitive material, a thermoplastic material or an index matching fluid. The adhesive material may be Norland 65 brand adhesive sold by Norland Optical Adhesives of New Brunswick, New Jersey. A suitable

thermoplastic material for use with plastic substrates, may be a thermoplastic adhesive such as an adhesive known as Meltmount sold by R.P. Cargile Laboratories, Inc. of Cedar Grove, New Jersey.

The top display 22 is closest to or faces a viewer V of the display 20 and the bottom

display 24 is "stacked" or disposed vertically below the top display 22, that is, away from the viewer V in a direction shown by the arrow in Figures 1, 2 and 3. The two displays 22, 24

have vertically aligned image pixels providing for improved brightness of reflective portions of an image displayed on the display 20 as seen by the viewer. Two representative image pixels Pl(xi, yj), P2(xi, yj) which are vertically aligned are shown in Figures 1, 2 and 3. The vertical alignment of image pixels increases the brightness of the image reflective portions. Brightness is defined herein as the % reflectivity of the wavelength at which there is maximum reflection. A standard white diffuse reflector has a reflectivity of 100% on the scale used.

Typically, each of the displays 22, 24 has a brightness of approximately 35-40% for reflective portions of displayed images. When the displays 22, 24 are stacked as in the present invention, the brightness of the top display 22 is reinforced by that of the second display 24

resulting in a combined brightness on the order of 50% for the reflective portions of the displayed image as seen by the viewer V looking at the display in the direction of the arrow.

Thus, the stacked display 20 of the present invention results in enhanced brightness of the

reflective image pixels of the display 20 as seen by the eye of the viewer V looking at the display in the direction of the arrow.

The upper display 22 is comprised of a first rectangular substrate 30a (closest to the viewer) and a second rectangular substrate 28a, between which is disposed a thin layer of

cholesteric liquid crystal material 34a. The substrates may be formed of glass (e.g., 0.5 millimeters (mm.) to 1.5 mm. thick) or of plastic (e.g., 0.018 mm. or approximately 7 mils

thick), which materials are well known in the liquid crystal art. The liquid crystal material may be filled into a cell spacing between substrates of, for example, at least 2 microns, more specifically, from about 4 microns to about 6 microns or even about 10 microns or greater, in a manner known to those skilled in the art. The display 22 may have the same or a different cell spacing than the display 24. The first substrate 30a includes a set of 640 column electrode segments 39 affixed to an inwardly facing surface of the substrate 30a. Preferably, the set of column electrodes 39 comprise an array of parallel indium tin oxide (ITO) traces coated on the inwardly facing surface. The second substrate 28a includes a set of 480 row electrode

segments 37 affixed to an inwardly facing surface of the substrate 28a. Preferably, the set of row electrodes 37 comprise an array of parallel ITO traces coated on the inwardly facing surface. Similar to the upper display 22, the lower display 24 is comprised of a first substrate

30b (furthest from the viewer) and a second substrate 28b spaced apart by a thin layer of

cholesteric liquid crystal material 34b. The first substrate 30b includes a set of 640 column electrodes 40 affixed to an inwardly facing surface of the substrate 30b. Preferably, the set of column electrodes 40 comprise an array of parallel ITO traces coated on the inwardly facing surface. The second substrate 28b includes a set of 480 row electrodes 38 affixed to an

inwardly facing surface of the substrate 28b. Preferably, the set of row electrodes 38 comprise

an array of parallel ITO traces coated on the inwardly facing surface. A layer of a radiation

adsorptive material C is applied such as by painting the back of the display. One suitable material is black paint that absorbs visible light. As can best be seen in Figures 1, 2 and 3, the sets of row electrodes 37, 38 extend

orthogonally to the column electrodes 39, 40. The set of row electrodes 37 of the top display 22 are electrically connected to the set of row electrodes 38 of the bottom display 24 via a

preferably flexible interconnect 44. Likewise, as can best be seen in Figure 3, the set of

column electrodes 39 of the top display 22 are electrically connected to the set of column electrodes 40 of the bottom display 24 via a preferably flexible interconnect 43. Drive electronics are shown schematically in Figure 8 at 200 and comprise a set of row driver circuitry (shown schematically at 202 mounted on a row driver board 202a) and a set of column driver circuitry (shown schematically at 204 mounted on a column driver board 204a). The set of row driver circuitry 202 is connected to either the top display row electrodes 37 or

the bottom display row electrodes 38. Likewise, the set of column driver circuitry 204 is

connected to either the top display column electrodes 39 or the bottom display column electrodes 40. The flexible interconnects 43, 44 are advantageous in that they enable the drive electronics 200 comprising a single set of row driver circuitry 202 and column driver circuitry 204 to drive both the row and column electrodes 37, 39 of the top display 22 simultaneously with the row and column electrodes 38, 40 of the bottom display 24. Thus, the stacked

display 20 is driven with one set of drive electronics 200. A suitable flexible interconnect is the pressure fastenable Zebra® elastomeric connectors sold by Fujipoly America Corporation of Kenil worth, New Jersey. Referring now to Figures 4 through 7, there is seen an example of means for

assembling an embodiment of the stacked display 20 comprising fully assembled first and

second displays 22 and 24. As shown in Figures 3-6, the column electrodes 39 of the top

substrate 30a of the first display 22 are electrically connected to the column electrodes 40 of

the bottom substrate 30b of the second display 24 using the flexible connector 43. This is the

first step in electrically connecting the column and row electrodes of the two displays because, due to the stepped positioning of the substrates, the electrodes can be easily accessed as shown in Figure 4. The displays 22, 24 are then folded together (Figure 5) so that the first display 22 moves into registry atop and parallel to the second display 24. The index matching material 26 is disposed between the two displays 22, 24 by spreading it on or by filling. As shown in Figures 2 and 7, the row electrodes 37 of the bottom substrate 28a of the first display 22 are electrically connected to the row electrodes 38 of the upper substrate 28b of the second display 24 using the connector 44. This is facilitated by the inner substrates

being stepped, which exposes the electrode traces. That is, the flexible connector 44 is bent around the outside of the protruding or extending portions of the substrates 28a, 28b.

Although the flexible connectors 43 and 44 are preferably electrically connected to the displays in the manner shown in Figures 4-7, the present invention also contemplates and encompasses other ways for connecting the row and column electrodes of one of the displays with the row

and column electrodes of another of the displays, which would be apparent to those skilled in the art in view of this disclosure. For example, one may stack displays that have not been first fully assembled. One may assemble each of the displays after the connector 43 is applied to interconnect the ITO traces 39, 40 as shown in Fig. 4. This may be the case when employing pressure fastenable Zebra® elastomeric connectors by Fujipoly.

As shown in Figure 8 in block diagram form, display driver circuitry 100 includes the

drive electronics 200 and a control and logic unit 150 is attached to the stacked display 20.

The drive electronics 200 comprises the row driver circuitry 202, including row drivers

mounted on the row driver board 202a, and the column driver circuitry 204, including column drivers mounted on the column driver board 204a. The row and column driver circuitry 202,

204 are preferably each mounted on a printed circuit board. Control voltages are coupled to the respective row and column electrodes using (e.g., heat sealable) interconnects 203, 205

coupled to the bottom column electrodes 40 and the top row electrodes 37, as described in the previous electrical interconnection of substrates. As shown in Figure 6, the connector 203 is positioned so that electrical traces on the connector 203 are aligned with the column electrodes 40 on the substrate 30b of the second display 24. Similarly, interconnect material 205 is positioned so that electrical traces on the connector 205 are aligned with the row electrodes 37 on the substrate 28a of the first display 22. A full discussion of an appropriate drive scheme is disclosed in U.S. Application Serial No. 08/868,709, filed June 4, 1997 and entitled CUMULATIVE DRIVE SCHEME AND METHOD FOR A LIQUID CRYSTAL

DISPLAY. U.S. application Serial No. 08/868,709 is assigned to the assignee of the present invention and is incorporated herein in its entirety by reference.

The interconnects 43 and 44 between displays and the interconnects 203 and 205

between the drive electronics and the displays, may be in the form of any suitable electrical connectors. One suitable form of connector is a heat sealable connector by Elform, Inc. of

Reno, Nevada, such as is described in the article, Reinke, R., Interconnecting Flex Circuitry to

Rigid Circuitry Using Anisotropic Conductive Thermoset Film, date unknown, which is incorporated herein by reference in its entirety. One skilled in the art would understand how

such flexible interconnects are bonded onto the substrates on the ITO traces in view of the information containing herein and in the Reinke article. Another suitable form of interconnect is Kapton™ connectors by Dow Chemical Company of Midland, Michigan. Yet another interconnect is Zebra® elastomeric connectors by Fujipoly, which have a greater thickness than

the intended cell spacing and thus, are connected by pressure between substrates during cell

fabrication. One skilled in the art would realize in view of this disclosure, how to fasten the

electrical connectors to the displays of the present invention. The row driver 202a is mounted on the row driver board and has its output channels

coupled to different row electrode segments via suitable edge connections (shown schematically in Figure 8). Similarly, the column driver 204a is mounted on a column driver

board and has its output channels coupled to different column electrode segments via suitable edge connections (also shown schematically in Figure 8). The row and column driver circuitry 202, 204 is electrically connected to the logic and control unit 150 which includes circuitry that controls the presentation of data on the display 20 by controlling the reflectance state of each pixel in the array of 307,200 pixels that make up

the display 20. A microprocessor controls operations of the circuitry of the control and logic unit 150.

Voltage levels at which each of the displays is addressed, are made the same for each liquid crystal layer. Typically, a liquid crystal display that reflects light of one wavelength, such as blue, is operated at a different voltage level than a liquid crystal display that reflects light of a different wavelength, such as yellow. In the stacked display apparatus of the present invention, each liquid crystal display is constructed so as to accommodate the same voltage levels by selecting at least one of certain material properties such as e, viscosity and pitch length, as well as certain cell spacing.

The stacked display 20 of the present invention has principally been described in terms of the electrical connections and drive electronics that enable operation of the display. It will

be apparent to one skilled in the art in view of this disclosure and that of U.S. application

Serial No. 08/823,329 referenced above, that the display 20 may include various suitable

materials and components even though not addressed here, such as alignment layers,

passivation layers, surface treatments, contrast improving or color enhancing layers (black or

colored) either at the back of the stacked display or on one of the substrates inside the stacked display, liquid crystal materials and liquid crystal additives for affecting the performance of the

display.

In particular, one application is a stacked display in which the lower display reflects

infrared radiation and the upper display reflects visible radiation, as disclosed in U.S. Application Serial No. 08/823,329. Any number of visible displays may be stacked above the infrared display and may be driven with the infrared display or may be driven independently from the infrared display and other displays.

Another preferred aspect of the invention is a stacked display including a blue

reflecting top chiral nematic layer followed by a yellow reflecting chiral nematic back layer and an optional lower infrared reflecting layer. With no infrared back layer, a black layer would be

disposed downstream of the back yellow-reflecting display. When the infrared display is used, a layer would be disposed between the infrared layer and the yellow-reflecting liquid crystal layer, which absorbs visible light but permits the transmission of infrared light therethrough, as disclosed in U.S. application Serial No. 08/823,329. An absorptive black layer would be disposed downstream of the infrared reflecting layer. Those skilled in the art would appreciate in reading this application that colored layers may be used instead of black layers in the present

invention. At least two of the displays are electrically connected according to the present invention to enable them to be driven together. Additional layers may be used and driven with these layers or driven independently. For example, the blue reflecting layer, the yellow reflecting layer and the infrared reflecting layer may be driven together in accordance with the

present invention. When the electrodes bounding the blue and yellow layers are energized to place the liquid crystal in both displays in the reflecting twisted planar state, the viewer sees

white light reflected from the display. When both of the visible displays are in the focal conic

state, the viewer sees the black back layer. Thus, a black and white display is formed. If the infrared-reflecting display is employed in the stacked display device, at night the viewer can see the display using night vision goggles as is described in U.S. application Serial No.

08/823,329, referenced above.

By utilizing gray scale as disclosed in U.S. Application Serial No. 08/823,329 and in U.S. Patent No. 5,453,863 issued September 26, 1995 to West entitled "MULTISTABLE CHIRAL NEMATIC DISPLAYS," which is incorporated herein by reference in its entirety,

one or more displays of the stacked assembly may be made to reflect light having any wavelength at various intensities. Thus, the color of the visible light reflecting displays can be varied. While the invention has been described herein in its currently preferred embodiment or embodiments, those skilled in the art will recognize that other modifications may be made

without departing from the invention and it is intended to claim all modifications and variations as fall within the scope of the invention.

Claims

What is claimed is:

1. A stacked display apparatus comprising: a) first and second layers of chiral nematic liquid crystal material; b) substrates bounding said first layer of liquid crystal material and said second layer of liquid crystal material so as to prevent communication between said first layer of liquid crystal material and said second layer of liquid crystal material; c) first row and first column conductive electrodes disposed on the substrates bounding said first liquid crystal layer and second row and second column conductive

electrodes disposed on the substrates bounding said second liquid crystal layer, wherein said first row electrodes extend transverse to and on a different substrate than said first column electrodes and said second row electrodes extend transverse to and on a different substrate than said second column electrodes;

d) electrical conductors interconnecting said first row electrodes and said second row electrodes and electrical conductors interconnecting said first column electrodes and said

second column electrodes; e) row driver electronics electrically coupled to one of said first row electrodes

and said second row electrodes for applying voltage to both said first row electrodes and said

second row electrodes; and

f) column driver electronics electrically coupled to one of said first column

electrodes and said second column electrodes for applying voltage to both said first column electrodes and said second column electrodes.

2. The stacked display apparatus of claim 1, wherein said liquid crystal material of

said first layer has a twist sense opposite to said liquid crystal material of said second layer.

3. The stacked display apparatus of claim 1, wherein one of said liquid crystal material of said first layer and said liquid crystal material of said second layer has chiral material of a pitch length effective to reflect light in a visible portion of the electromagnetic

spectrum and the other of said liquid crystal material of said first layer and said liquid crystal material of said second layer has chiral material of a pitch length effective to reflect light in an infrared portion of the electromagnetic spectrum.

4. The stacked display apparatus of claim 3, wherein said second layer is disposed above said first layer and is closer to a viewer than said first layer, and said liquid crystal material of said first layer comprises said infrared reflecting chiral material and said liquid crystal material of said second layer comprises said visible reflecting chiral material.

5. The stacked display apparatus of claim 1, wherein said electrical conductors are comprised of a flexible material.

6. The stacked display apparatus of claim 5, wherein said flexible material has a composition effective to be heat sealed to the substrates.

7. The stacked display apparatus of claim 5 wherein said flexible material has a composition effective to be fastened to the substrates by pressure.

8. The stacked display apparatus of claim 1 wherein said liquid crystal material of said first layer comprises chiral material of a pitch length effective to reflect visible light of a first color and said liquid crystal material of said second layer comprises chiral material of a pitch length effective to reflect visible light of a second color different than said first color.

9. The stacked display apparatus of claim 1 comprising a first substrate and a second substrate bounding said first layer of liquid crystal material and said second substrate

and a third substrate bounding said second layer of liquid crystal material.

10. The stacked display apparatus of claim 1 comprising a first substrate and a second substrate bounding said first layer of liquid crystal material and a third substrate and a fourth substrate bounding said second layer of liquid crystal material.

11. The stacked display apparatus of claim 1 comprising: at least an additional layer of liquid crystal material; and substrates bounding each said additional layer of liquid crystal material, said electrical conductors interconnecting said first row electrodes, said second row electrodes and row electrodes for each said additional layer, and said electrical conductors interconnecting said first column electrodes, said second column electrodes and said column

electrodes for each said additional layer, said row driver electronics being electrically

connected to one of said first row electrodes, said second row electrodes and said row electrodes of said additional layer, and said column driver electronics being electrically connected to one of said first column electrodes, said second column electrodes and said

column electrodes of said additional layer.

12. The stacked display apparatus of claim 1 wherein said electrical conductors are

electrically coupled only on substantially exterior portions of the substrates.

13. The stacked display apparatus of claim 4 further comprising a layer of material disposed between said first layer and said second layer which permits passage of infrared radiation and prevents passage of visible radiation therethrough.

14. A method of assembling a stacked display apparatus, comprising the steps of:

a) providing first and second layers of chiral nematic liquid crystal material; said first layer of liquid crystal material being bound by first layer substrates, one of which includes first row conductive electrodes disposed thereon and one of which includes first column

conductive electrodes disposed thereon that extend transverse to the first row electrodes, said second layer of liquid crystal material being bound by second layer substrates, one of which includes second row conductive electrodes disposed thereon and one of which includes second column conductive electrodes disposed thereon that extend transverse to the second row electrodes; b) electrically coupling said first column electrodes and said second column

electrodes via a first flexible conductive interconnect; c) folding said first and second liquid crystal layers so that said substrates are stacked relative to one another; and

d) electrically coupling said first row electrodes and said second row electrodes

via a second flexible conductive interconnect.

15. A method for assembling a stacked liquid crystal display comprising the steps

of: a) providing first and second layers of chiral nematic liquid crystal material, each

layer being bound by first and second substrates, the first substrates having row electrodes disposed thereon, the second substrates having column electrodes disposed thereon; b) orienting the first and second substrates bounding the first layer of liquid crystal

material so that row electrodes disposed on the first substrate extend transverse to column electrodes disposed on the second substrate; c) orienting the first and second substrates bounding the second layer of liquid crystal material so that row electrodes disposed on the first substrate extend transverse to column electrodes disposed on the second substrate; d) electrically connecting the row electrodes of the first substrate of the first liquid crystal layer to the row electrodes of the first substrate of the second liquid crystal layer; e) electrically connecting the column electrodes of the second substrate of the first

liquid crystal layer to the column electrodes of the second substrate of the second liquid crystal layer; and

f) coupling row driver electronics to the row electrodes of one of the first substrates and column driver electronics to the column electrodes of one of the second

substrates.

16. A stacked display apparatus comprising:

a) first and second layers of liquid crystal material; b) substrates bounding said first layer of liquid crystal material and said second layer of liquid crystal material so as to prevent communication between said first layer of liquid

crystal material and said second layer of liquid crystal material; c) a first set and a second set of conductive electrodes disposed on the substrates bounding said first liquid crystal layer and third set and a fourth set of conductive electrodes

disposed on the substrates bounding said second liquid crystal layer, wherein said first set of electrodes are on a different substrate than said second set of electrodes and said third set of electrodes are on a different substrate than said fourth set of column electrodes; d) electrical conductors interconnecting said first set of electrodes and said third set of electrodes and electrical conductors interconnecting said second set of electrodes and said fourth set of electrodes; e) first driver electronics electrically coupled to one of said first and third sets of electrodes for applying voltage to both of said first and third sets of electrodes; and

f) second driver electronics electrically coupled to one of said second and fourth sets of electrodes for applying voltage to both of said second and fourth sets of electrodes.

17. The stacked display apparatus of claim 16 wherein the first set of electrodes extend transverse to the second set of electrodes and the third set of electrodes extend transverse to the fourth set of electrodes, the first and the third sets of electrodes comprising

first and second sets of row electrodes and the second and fourth sets of electrodes comprising first and second sets of column electrodes and the first driver electronics comprising row driver electronics and the second driver electronics comprising column driver electronics.

18. The stacked display apparatus of claim 16 wherein the first and second layers

of liquid crystal material are chiral nematic liquid crystal material.

19. The stacked display apparatus of claim 18, wherein said liquid crystal material of said first layer has a twist sense opposite to said liquid crystal material of said second layer.

20. The stacked display apparatus of claim 18, wherein said liquid crystal material of said first layer has a twist sense substantially the same as said liquid crystal material of said second layer.

21. The stacked display apparatus of claim 18, wherein one of said liquid crystal

material of said first layer and said liquid crystal material of said second layer has chiral material of a pitch length effective to reflect light in a visible portion of the electromagnetic spectrum and the other of said liquid crystal material of said first layer and said liquid crystal material of said second layer has chiral material of a pitch length effective to reflect light in an infrared portion of the electromagnetic spectrum.

22. The stacked display apparatus of claim 21, wherein said second layer is disposed above said first layer and is closer to a viewer than said first layer, and said liquid crystal material of said first layer comprises said infrared reflecting chiral material and said liquid crystal material of said second layer comprises said visible reflecting chiral material.

23. The stacked display apparatus of claim 16 wherein said electrical conductors are comprised of a flexible material.

24. The stacked display apparatus of claim 23, wherein said flexible material has a composition effective to be heat sealed to the substrates.

25. The stacked display apparatus of claim 23 wherein said flexible material has a composition effective to be fastened to the substrates by pressure.

26. The stacked display apparatus of claim 18 wherein said liquid crystal material of said first layer comprises chiral material of a pitch length effective to reflect visible light of a first color and said liquid crystal material of said second layer comprises chiral material of a pitch length effective to reflect visible light of a second color different than said first color.

27. The stacked display apparatus of claim 16 comprising a first substrate and a second substrate bounding said first layer of liquid crystal material and said second substrate and a third substrate bounding said second layer of liquid crystal material.

28. The stacked display apparatus of claim 16 comprising a first substrate and a second substrate bounding said first layer of liquid crystal material and a third substrate and a fourth substrate bounding said second layer of liquid crystal material.

29. The stacked display apparatus of claim 17 comprising: at least an additional layer of liquid crystal material; and substrates bounding each said additional layer of liquid crystal material, said electrical conductors interconnecting said first row electrodes, said

second row electrodes and row electrodes for each said additional layer, and said electrical

conductors interconnecting said first column electrodes, said second column electrodes and said column electrodes for each said additional layer, said row driver electronics being

electrically connected to one of said first row electrodes, said second row electrodes and said row electrodes of said additional layer, and said column driver electronics being electrically

connected to one of said first column electrodes, said second column electrodes and said column electrodes of said additional layer.

30. The stacked display apparatus of claim 16 wherein said electrical conductors are electrically coupled only on substantially exterior portions of the substrates.

31. The stacked display apparatus of claim 21 further comprising a layer of material disposed between said first layer and said second layer which permits passage of infrared radiation and prevents passage of visible radiation therethrough.

32. A method of assembling a stacked display apparatus, comprising the steps of: a) providing first and second layers of liquid crystal material; said first layer of liquid crystal material being bound by first layer substrates, one of which includes first set of conductive electrodes disposed thereon and one of which includes second set of conductive electrodes disposed thereon, said second layer of liquid crystal material being bound by second layer substrates, one of which includes third set of conductive electrodes disposed thereon and

one of which includes a fourth set of conductive electrodes disposed thereon;

b) electrically coupling said second set of electrodes and said fourth set of electrodes via a first flexible conductive interconnect; c) folding said first and second liquid crystal layers so that said substrates are

stacked relative to one another; and

d) electrically coupling said first set of electrodes and said second set of electrodes

via a second flexible conductive interconnect.

33. A method for assembling a stacked liquid crystal display comprising the steps

of: a) providing first and second layers of liquid crystal material, each layer being bound by first and second substrates, the first substrates having row electrodes disposed thereon, the second substrates having column electrodes disposed thereon; b) orienting the first and second substrates bounding the first layer of liquid crystal material so that row electrodes disposed on the first substrate extend transverse to column electrodes disposed on the second substrate; c) orienting the first and second substrates bounding the second layer of liquid

crystal material so that row electrodes disposed on the first substrate extend transverse to column electrodes disposed on the second substrate;

d) electrically connecting the row electrodes of the first substrate of the first liquid crystal layer to the row electrodes of the first substrate of the second liquid crystal layer; e) electrically connecting the column electrodes of the second substrate of the first liquid crystal layer to the column electrodes of the second substrate of the second liquid crystal layer; and

f) coupling row driver electronics to the row electrodes of one of the first substrates and column driver electronics to the column electrodes of one of the second substrates.