United States Patent [191
`Hatano et al.
`
`lllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll
`US005090794A
`5,090,794
`[11] Patent Number:
`Feb. 25, 1992
`[45] Date of Patent:
`
`[54] METHOD FOR DRIVING A
`MULTI-LAYERED-TYPE LIQUID CRYSTAL
`DISPLAY DEVICE
`[75] Inventors: Akitsugu l-latano; Yutaka Ishii, both
`of Nara, Japan
`[73] Assignee: Sharp Kabushiki Kaisha, Osaka,
`Japan
`[21] Appl. No.: 439,876
`[22] Filed:
`Nov. 21, 1989
`[30]
`Foreign Application Priority Data
`Nov. 21, 1988 [JP]
`Japan .............................. .. 63-294373
`
`[51] Int. Cl.5 .............................................. .. G02F 1/13
`[52] U.S. Cl. ...................................... .. 359/53; 359/85;
`359/93
`[58] Field of Search ............. .. 350/335, 347 E, 347 R,
`350/332
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,241,339 12/1980 Ushiyama et al. ................ ., 350/335
`4,396,250 8/1983 Wada et a]. ....................... .. 350/335
`4,443,065 4/l984 Funada et al. ................ .. 350/335
`
`4,460,248 7/1984 Shirai . . . . . . . . . . . . . . .
`
`. . . . . .. 350/335
`
`4,556,286 12/1985 Uchida et al. . . . .
`
`. . . . . .. 350/335
`
`350/347 E
`4,653,865 3/1987 Kando et al7
`4,904,058 2/1990 Kato et al. ........................ .. 350/335
`4,941,737 7/1990 Kimura ............................. .. 350/335
`
`FOREIGN PATENT DOCUMENTS
`
`0246842 11/1987 European Pat. Off. .
`0284372 9/1988 European Pat. Off. .
`“B6802 3/1980 Japan ................................. .. 350/335
`
`0067817 6/1981 Japan ................................. .. 350/335
`0019123 1/1985 Japan ................................. .. 350/335
`62-283684 11/1987 Japan .
`WO8903542 4/1989 PCT Int’l App]. .
`
`OTHER PUBLICATIONS
`“Multicolor Display by Double-Layered Supertwis
`ted-Nematic LCD”, to Kimura et al.
`"New Multicolor Liquid Crystal Displays that Use a
`Twisted Nematic Electro-Optical Cell”, by Terry J.
`Scheffer, J. Appl. Phys, vol. 44, No. 11, Nov. 73.
`“Neutralized Supertwisted Nematic LCD: Principle
`and Characteristics", by Mitsuo Nagata et al., The
`Transactions of the IEICE, vol. E-7l, No. 11, Nov. 88.
`Primary Examiner-Rolf Hille
`Assistant Examiner—Tan Ho
`[57]
`ABSTRACT
`A method for driving a multi-layered-type liquid crystal
`display device is disclosed. The liquid crystal display
`device includes a plurality of cell layers, and each cell
`layer contains liquid crystal molecules twisted between
`two transparent substrates so as to have a relatively
`large birefringence and having a light transmittance
`changing responsive to a voltage applied thereto. Volt~
`ages to be applied to respective cell layers are deter
`mined so as to pass a predetermined color light in com
`bination of the light transmittances of individual cell
`layers. Further, these cell layers are driven by those
`voltages determined to display an image having the
`predetermined color light on the liquid crystal display
`device.
`
`11 Claims, 8 Drawing Sheets
`
`6U“ 6i 71”
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`Patent Owner’s Exhibit 2001
`IPR2015-00021
`Page 1 of 16
`
`

`

`US. Patent
`
`Feb. 25, 1992
`
`Sheet 1 of 8
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`5,090,794
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`Direction of
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`Patent Owner’s Exhibit 2001
`IPR2015-00021
`Page 2 of 16
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`US. Patent
`
`Feb. 25, 1992
`
`Sheet 2 of 8
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`5,090,794
`
`Fig.3
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`Patent Owner’s Exhibit 2001
`IPR2015-00021
`Page 3 of 16
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`U.S. Patent
`
`Feb. 25, 1992
`
`Sheet 3 of 8
`
`5,090,794
`
`Fig . 4a
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`
`Patent Owner’s Exhibit 2001
`IPR2015-00021
`Page 4 of 16
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`

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`US. Patent
`
`Feb. 25, 1992
`
`Sheet ‘4 of 8
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`5,090,794
`
`80
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`
`Patent Owner’s Exhibit 2001
`IPR2015-00021
`Page 5 of 16
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`US. Patent
`
`Feb. 25, 1992
`
`Sheet 5 of 8
`
`5,090,794
`
`Fig. 5a
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`m w w w.
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`
`Patent Owner’s Exhibit 2001
`IPR2015-00021
`Page 6 of 16
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`

`

`US. Patent
`
`m. 25, 1992
`
`sheet 6 of 8
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`' 5,090,794
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`
`Patent Owner’s Exhibit 2001
`IPR2015-00021
`Page 7 of 16
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`_ US. Patent
`
`Feb. 25, 1992
`
`Sheet 7 of 8
`
`5,090,794
`
`
`
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`
`0 4
`
`20
`
`Voltoge[V]opplied to liquid crystal cell 1
`
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`IPR2015-00021
`Page 8 of 16
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`US. Patent
`
`Feb. 25, 1992
`
`Sheet 8 of 8
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`5,090,794
`
`100 -
`
`8
`0
`
`60‘
`
`O 0 4 2
`
`
`
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`
`voltogelvlopplied to liquid crystal cell i
`
`Patent Owner’s Exhibit 2001
`IPR2015-00021
`Page 9 of 16
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`

`

`1
`
`5,090,794
`
`METHOD FOR DRIVING A
`MULTI-LAYERED-TYPE LIQUID CRYSTAL
`DISPLAY DEVICE
`
`2
`ity of the threshold value, and it is possible to obtain a
`high contrast ratio even under a high duty ratio. How
`ever, because it utilizes the birefringence effect of the
`liquid crystal, the dependence of the display character
`istics on the wavelength of light is higher than that of
`the TN display. Thereby, coloring of the display be
`comes much more severe.
`Furthermore, in order to display a multicolor image,
`generally, a color ?lter layer is provided as described
`above. In this case, however, there are such problems
`that the manufacturing process therefor is complicated
`and the manufacturing cost increases.
`
`20
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention relates to a method for driving
`a liquid crystal display device, and more particularly, to
`a method for driving multi-layered-type liquid crystal
`display device comprising stacked plural liquid crystal
`cells for passing lights of different colors therethrough.
`2. Description of Related Art
`Liquid crystal display devices are now being used
`widely used in various electronic apparatuses such as
`clocks and electronic calculating machines, displays of
`computer’s terminals and word processors, television
`sets. Recently, there have been extremely high demands
`for constituting multicolor and full color displays using
`by liquid crystal display devices. Further, some are
`already put in practical use in the ?elds of graphic dis
`play and image display. The color display of this type is
`attained by arranging color ?lter layers inside of a liquid
`crystal cell as a light switcher in order to generate vari
`ous colors. The major display mode of the liquid crystal
`display device is called a twisted nematic display mode
`(referred to as a TN display mode hereinafter), wherein
`liquid crystal molecules are twisted by an angle of 90° in
`the liquid crystal cell.
`However, in the TN display mode, the dependency
`of the display characteristic on the wavelength of light
`is relatively large, and it is dif?cult to switch the light
`uniformly over the whole range of the visible light.
`Particularly, in a normally closed type liquid crystal
`display device in which the polarization axes of two
`polarizers are parallel to each other, coloring of the
`display may be caused due to leakage of the light when
`no voltage is applied to the liquid crystal layer. There
`fore, it is dif?cult to adapt the TN display mode in a full
`color display.
`In a color liquid crystal display device utilizing the
`TN display mode, wherein the aforementioned color
`?lter layer are arranged, there have been mainly pro
`posed the following two driving methods as methods
`for driving the color liquid crystal display device. One
`45
`is an active matrix driving method, and another is a
`simple multiplex driving method.
`In a liquid crystal display device utilizing the active
`matrix driving method, non-linear devices such as di
`odes or switching devices such as thin ?lm transistors
`are provided at respective pixels of the liquid crystal
`cell, and the liquid crystal layer of each pixel is driven
`selectively.
`In a liquid crystal display device utilizing the simple
`multiplex driving method, there are not provided non
`linear devices or switching devices, and the liquid crys
`tal layer of each pixel is driven sequentially. In this
`liquid crystal display device, a steepness near the
`threshold value gives a trouble among optical charac
`teristics of the liquid crystal, in which the TN display
`mode is used.
`In order to improve the optical characteristics exhib
`iting the steepness near the threshold value, there has
`been proposed a Super Twisted Nematic method (re
`ferred to as an STN method hereinafter) as a method for
`orienting liquid crystal molecules, wherein the twisted
`angle is set so as to have a value between 180' and 270‘.
`In the STN method, the curve rises steeply in the vicin
`
`SUMMARY OF THE INVENTION
`An essential object of the present invention is to pro
`vide a method for driving a multi-layered-type liquid
`crystal display device, which is capable of displaying
`multicolor images in a high quality without using any
`color ?lter.
`In order to accomplish the above object, according to
`the present invention, there is provided a method for
`driving a multi-layered-type liquid crystal display de
`vice comprising stacked plural cell layers, each said cell
`layer containing liquid crystal molecules twisted be
`tween two transparent substrates so as to have a rela
`tively large birefringence and having a light transmit
`tance changing responsive to a voltage applied thereto.
`The method is characterized in that voltages to be ap
`plied to respective cell layers are determined so as to
`pass a predetermined color light in combination of the
`light transmittances of individual cell layers, and that
`these cell layers are driven by those voltages deter
`mined to display an image having said predetermined
`color light on said liquid crystal display device.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`These and other objects and features of the present
`invention will become clear from the following descrip
`tion taken in conjunction with the preferred embodi
`ments thereof with reference to the accompanying
`drawings, in which:
`FIG. 1 is a cross sectional view showing a fundamen
`tal structure of a double-layered-type liquid crystal
`display device of preferred embodiments according to
`the present invention;
`FIGS. 20 and 2b are diagrams schematically showing
`twists of liquid crystal molecules in left and right direc
`tions, respectively;
`FIG. 3 is a graph of characteristic curves showing the
`relation between a twist angle 91 of a liquid crystal layer
`of a double-layered-type liquid crystal and a contrast
`ratio of a displayed monochromatic image;
`FIG. 4a is a graph of R, G and B characteristic curves
`showing a relation between a voltage applied to a liquid
`crystal cell layer 1 and a light transmittance when a
`voltage is applied to a liquid crystal cell layer 2 in the
`double-layered type liquid crystal display device of a
`?rst preferred embodiment;
`FIG. 4b is a graph of R, G and B characteristic curves
`showing a relation between a voltage applied to the
`liquid crystal cell layer 1 and a light transmittance when
`no voltage is applied to the liquid crystal cell layer 2 in
`the double-layered-type liquid crystal display device of
`the ?rst preferred embodiment;
`FIG. 5a is a graph of R, G and B characteristic curves
`showing the relation between a voltage applied to a
`liquid crystal cell layer 1 and a light transmittance when
`
`55
`
`60
`
`65
`
`Patent Owner’s Exhibit 2001
`IPR2015-00021
`Page 10 of 16
`
`

`

`5,090,794
`
`3
`a voltage is applied to a liquid crystal cell layer 2 in a
`double-layered~type liquid crystal display device of a
`second preferred embodiment;
`FIG. 5b is a graph of R, G and B characteristic curves
`showing the relation between a voltage applied to the
`liquid crystal cell layer 1 and a light transmittance when
`no voltage is applied to the liquid crystal cell layer 2 in
`the double-layered-type liquid crystal display device of
`the second preferred embodiment;
`FIG. 6a is a graph of R, G and B characteristic curves
`showing the relation between a voltage applied to a
`liquid crystal cell layer 1 and a light transmittance when
`a voltage is applied to a liquid crystal cell layer 2 in a
`double-layered-type liquid crystal display device of a
`third preferred embodiment; and
`FIG. 6b is a graph of R, G and B characteristic curves
`showing the relation between a voltage applied to the
`liquid crystal cell layer 1 and a light transmittance when
`no voltage is applied to the liquid crystal cell layer 2 in
`the double-layered-type liquid crystal display device of
`20
`the third preferred embodiment.
`
`15
`
`25
`
`35
`
`45
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`Preferred embodiments according to the present in
`vention will be described below with reference to the
`attached drawings.
`First Preferred Embodiment
`FIG. 1 is a cross sectional view showing a fundamen
`tal structure of a double-layered-type liquid crystal
`device to which there is applied a driving method of a
`?rst preferred embodiment according to the present
`invention.
`Referring to FIG. 1, the liquid crystal display device
`has a double layered structure composed of ?rst and
`second cell layers 1 and 2, containing liquid crystal
`layers 60 and 6b, respectively. In the liquid crystal lay
`ers 6a and 6b, liquid crystal molecules are arranged in a
`twisted nematic phase.
`The ?rst and second cell layers 1 and 2 are formed so
`as to be stacked on both surfaces of a common transpar
`ent substrate 3b. The ?rst cell layer 1 has such a struc
`ture that the liquid crystal layer 60 is contained between
`two transparent substrates 3a and 3b and is sealed by a
`sealing element 70, and orientation membranes 50a and
`50b for orienting liquid crystal molecules in a twisted
`nematic phase are formed on respective inner surfaces
`of the transparent substrates 3a and 3b. The ?rst cell
`layer 1 has transparent electrical conductive electrode
`?lms 4a and 4b for applying a voltage to the liquid
`crystal layer 60, which are formed on respective inner
`surfaces of the transparent substrates 3a and 3b. Fur
`ther, there is formed a polarizer 8a on the outer surface
`of the outer substrate 3a
`The second cell layer 2 has such a_ structure that the
`liquid crystal layer 6b is contained between two trans
`parent substrates 3b and 3c and is sealed by a sealing
`element 7b, and orientation membranes Sba and 5bb for
`orienting liquid crystal molecules in a twisted nematic
`phase are formed on respective inner surfaces of the
`transparent substrates 3b and 3c.
`'
`The second cell layer 2 has transparent electrical
`conductive electrode ?lms 4c and 4d for applying a
`voltage to the liquid crystal layer 6b, which are formed
`on respective inner surfaces of the transparent sub
`strates 3b and 3c. Further, there is formed a polarizer 8b
`on the outer surface of the outer substrate 30 so that the
`
`4
`polarization axes of the polarizers 8a and 8b cross each
`other at an angle in the range from zero to 30".
`Each of the transparent substrates 3a to 30 may be
`made of glass, acrylic resin, or the like, and each of the
`transparent electrode ?lms 4a to 4c may be made of ITO
`which is a ?lm mainly made of indium oxide, a nesa
`?lm, or the like. Each of the orientation membranes Saa,
`Sab, Sba and Sbb may be made of an inorganic material
`such as SiO2, SiO, or the like or an organic material
`such as polyimide, polyvinyl alcohol, nylon, acrylic
`resin, or the like.
`In the liquid crystal device shown in FIG. 1, the axes
`of respective liquid crystal molecules in each of the
`liquid crystal layers 60 and 6b are twisted helically from
`the side of one substrate to the side of another substrate
`of each cell layer, as shown schematically in FIGS. 20
`and 2b. As is well known to those skilled in the art, the
`direction of twist is de?ned either a direction to the'
`right (FIG. 2a) or a direction to the left (FIG. 2b). In
`order to give a twisting power to individual liquid crys
`tal molecules, generally, at least one optically active
`material is added into the nematic liquid crystal. In the
`case of the right twist, for example, the material repre
`sented by the following general formula and offered by
`Merck & Co., Inc. is added thereinto.
`
`CH3
`
`On the other hand, in the case of the left twist, choles
`teryl nonanoate S-81l ® offered by Merck 8: Co., Inc.
`is added thereinto.
`In the double-layered-type liquid crystal display de
`vice, in order to enhance a contrast ratio in the case of
`a monochromatic display and a quality of the display in
`the case of a multicolor display, or the like, values 0|
`and 02 of twist angles of the liquid crystal layers 60 and
`6b in the ?rst and second cell layers 1 and 2, and the
`value An1-d1 of a product of the birefringence An] of the
`liquid crystal layer 60 and the thickness d] thereof and
`the value Az-dz of a product of the birefringence An; of
`the liquid crystal layer 6b and the thickness d2 thereof
`are adjusted so as to satisfy the following requirement.
`(a) The values Am-di and An2-d2 are adjusted so as to
`satisfy the following inequalities (l) and (2) in order to
`obtain the aforementioned excellent display characteris
`tics, which is con?rmed by the experiment performed
`by the inventors of the present invention.
`
`l.0< lAnz-dzl <3.5
`
`55
`
`(2)
`
`(b) In order to maximize the contrast ratio in the case
`of the monochromatic display, the values Anpdi and
`Anz-dz are adjusted so as to satisfy the following in
`equality (3), which is con?rmed by the experiment per
`formed by the inventors of the present invention.
`
`0.8<An2-d;/An|~d|<l.5
`
`(3)
`
`65
`
`(c) In order to display a monochromatic image by
`selectively applying an ON voltage for enabling light to
`pass through the liquid crystal layer 60 of the ?rst cell
`layer 1 or an OFF voltage for disabling light to pass
`therethrough to the liquid crystal layer 60 under the
`
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`Page 11 of 16
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`

`

`5,090,794
`
`5
`condition that a predetermined voltage is applied to the
`liquid crystal layer 60 of the ?rst cell layer 1, and also to
`display a multicolor image based on interference colors
`by selectively applying the aforementioned ON or OFF
`voltage to the liquid crystal layer 60 of the ?rst cell
`layer 1, the values An1-d1-01 and Amara; are adjusted
`so as to satisfy the following inequality (4), which is
`con?rmed by the experiment performed by the inven
`tors of the present invention.
`
`45
`
`6/360'—1<d/p_5_0/360'
`
`(6),
`
`wherein 6 is the twist angle of the liquid crystal. This
`requirement can be applied only to the case that the
`pretilt angle of the liquid crystal is equal to or smaller
`than about 10'. In the case that the pretilt angle thereof
`exceeds l0’, the range to be satis?ed by the ratio d/p
`becomes different from the range represented by the
`inequality (6).
`
`65
`
`In order to display a monochromatic image by selec
`tively applying the aforementioned ON or OFF voltage
`to the liquid crystal layer 60 of the ?rst cell layer 1
`under the condition that no voltage is applied to the
`liquid crystal layer 6b of the second cell layer 2, and also
`to display a multicolor image based on interference
`colors by selectively applying the aforementioned ON
`or OFF voltage to the liquid crystal layer 60 of the ?rst
`20
`cell layer 1, the values An1-d1-6i and Anpdg-G; are ad
`justed so as to satisfy the following inequality (5), which
`is con?rmed by the experiment performed by the inven
`tors of the present invention.
`
`25
`
`30
`
`35
`
`(d) FIG. 3 shows the relation between a twist angle
`61 of the liquid crystal layer 60 and a contrast ratio of a
`displayed monochromatic image in the double-layered
`type liquid crystal device. As shown in FIG. 3, each
`contrast ratio of displayed monochromatic images in
`the case of 02:01-30’ is larger than that in the case of
`01:62. Therefore, when the display contrast and the
`visibility are taken into consideration, the twist angle 61
`of the liquid crystal layer 60 of the ?rst cell layer 1 is
`preferably set so as to fall in the arrange from about 180°
`to about 360’. If the twist angle 01 exceeds 360“, do
`mains appear in the liquid crystal layer 6a in which each
`liquid crystal has an orientation disarrayed at the time of
`40
`the application of a predetermined voltage, resulting in
`a dispersion of light, which readily causes a decrease in
`the contrast.
`Furthermore, when the display contrast is taken into
`consideration, the twist angle 62 of the liquid crystal
`layer 6b of the second cell layer 2 is preferably set so as
`to fall in the range from about 30° to about 360° and to
`be different from the twist angle 81 of the liquid crystal
`layer 60 of the ?rst cell layer 1.
`In order to obtain a steep threshold characteristic in
`the contrast, the speci?c pitch p of the helical twist of
`liquid crystal is considered to be very important. The
`ratio d/p of the thickness d of each of the liquid crystal
`layers 60 and 6b to the pitch p of the helical twist of the
`liquid crystal therein is preferably set so as to satisfy the
`following relation, which is con?rmed by the experi
`ment performed by the inventors of the present inven
`tion.
`
`6
`FIGS. 40 and 4b are graphs of characteristic curves
`showing the relation between a voltage applied to the
`liquid crystal layer 6a of the ?rst cell layer 1 and a light
`transmittance in the double-layered-type liquid crystal
`device shown FIG. 1, wherein FIG. 4a shows the char
`acteristics in the case of a monochromatic display, and
`FIG. 4b shows the characteristics in the case of a multi
`color display.
`First of all, a method for driving the double-layered
`type liquid crystal device so as to display a monochro
`matic image and the action thereof will be described
`below with reference to FIG. 4a.
`Under the condition that a predetermined voltage is
`applied between the transparent electrode ?lms 4c and
`4d of the second cell layer 2 so as to be applied to the
`liquid crystal layer 6b, an ON voltage of about l.7 V or
`an OFF voltage of about 1.5 V is selectively applied
`between the transparent electrode ?lms 4a and 4b of the
`?rst cell layer 1 with use of a simple multiplex driving
`method so as to be applied to the liquid crystal layer 6a.
`Then, the orientation direction of the liquid crystal
`molecules on each pixel of an area of the liquid crystal
`layer 60 where the transparent electrode ?lms 4a and 4b
`cross each other changes according to the voltage ap
`plied thereto. The light having passed through the ?rst
`and second cell layers 1 and 2 passes through the polar
`izer 8b when the OFF voltage is applied to the liquid
`crystal layer 60. On the other hand, the light having
`passed through the ?rst and second layers 1 and 2 is
`shaded by the polarizer 8b when the ON voltage is
`applied thereto.
`Namely, as shown in FIG. 40, when red color light R
`having a wavelength of 610 nms, green color light G
`having a wavelength of 550 nms and blue color light B
`having a wavelength of 450 nms are incident substan
`tially perpendicularly to the outer surface of the polar
`izer 8a from the outer side thereof to the liquid crystal
`device, they pass through each partial area of the polar
`izer 8b corresponding to each of a ?rst group of pixels
`of the liquid crystal layer 6a to which the OFF voltage
`is applied. Then, a white color image is displayed on
`each of the ?rst group of pixels. On the other hand, the
`red color light R, the green color light G and the blue
`color light B are shaded by each partial area of the
`polarizer 8b corresponding to each of a second group of
`pixels of the liquid crystal layer 60 to which the ON
`voltage is applied. Then, a black color image is dis
`played on each of the second group of pixels. There
`fore, a monochromatic image composed of white and
`black color images is displayed on the double-layered
`type liquid crystal device. In the double-layered-type
`liquid crystal device, the second cell layer 2 acts as a
`compensator for compensating a color tone of the light
`having passed through the ?rst cell layer 1, resulting in
`an excellent monochromatic display without interfer
`ence colors.
`Next, a method for driving the double-layered-type
`liquid crystal device so as to display a multicolor image
`and the action thereof will be described below with
`reference to FIG. 4b.
`Under the condition that no voltage is applied to the
`liquid crystal layer 6b of the second cell layer 2, the ON
`or OFF voltage is selectively applied to the liquid crys
`tal layer 60 of the ?rst cell layer 1 in the manner similar
`to the case of the aforementioned monochromatic dis
`play. Then, as shown in FIG. 4b, the red color light R,
`the green color light G and the blue color light B are
`shaded by each partial area of the polarizer 8b corre
`
`Patent Owner’s Exhibit 2001
`IPR2015-00021
`Page 12 of 16
`
`

`

`5,090,794
`8
`7
`to 4d, orientation membranes 500, Sub, 5ba and Sbb of
`sponding to each of a ?rst group of pixels of the liquid
`crystal layer 60 to which the OFF voltage is applied.
`polyimide are formed with a thickness of about 500 A
`by a spin coating technique, the surfaces of which are
`Then, a black color image is displayed on each of the
`treated by rubbing with cloth, causing the liquid crystal
`?rst group of pixels. On the other hand, the light trans
`mittance of only the blue color light B on each of a
`molecules to be in a parallel orientation.
`A liquid crystal layer 60 of the ?rst cell layer 1 is
`second group of pixels corresponding to the liquid crys
`made of a liquid crystal ZLI-l69l made by Merck &
`tal layer 60 to which the ON voltage is applied in
`Co., Inc., to which 0.72 wt % of cholesteryl nonanoate
`creases, and then, a blue color image is displayed on
`is added as an optically active material. A liquid crystal
`each of the second group of pixels. Therefore, a two
`layer 6b of the second cell layer 2 is made of a liquid
`color image composed of black and blue color images is
`displayed on the double-layered-type liquid crystal de
`crystal ZLI-3449-000 made by Merck & Co , Inc., to
`vice. Namely, the characteristic of the function for
`which 1.0 wt % of CB-lS is added. The twist direction
`of the liquid crystal layer 60 is opposite to that of the
`compensating the color tone of the second cell layer 2
`liquid crystal layer 6b, and the twist angles 01 and 02 of
`changes by switching over from such a state that the
`predetermined voltage is applied to the liquid crystal
`the liquid crystal layers 60 and 6b are set at 240' and
`270°, respectively. The thickness d] of the ?rst cell layer
`layer 6b to such a state that no voltage is applied
`thereto, resulting in a change in the color of the dis
`1 is about 7 ttms, and the thickness d; of the second cell
`played image.
`layer 2 is about 12 urns. Furthermore, the pitch p of the
`helical twist of the liquid crystal layer 60 is about 14
`If the second cell layer 2 is driven statically so as to
`ums, and that of the liquid crystal layer 617 is about 20_
`switch over from such a state that the predetermined
`urns. The pretilt angle of each of the liquid crystal ar
`voltage is applied to the substantially whole area of the
`ranged between the orientation membranes Saa and Sab
`liquid crystal layer 6b to such a state that no voltage is
`and the liquid crystal arranged between the orientation
`applied thereto, the whole image surface of the double
`layered-type liquid crystal device can be switched over
`membranes She and 5bb are set at about 8‘. The polariz
`from a monochromatic display for selectively display
`ers 8a and 8b are made of a compound including iodine,
`ing a white color image or a black color image thereon
`and are formed on the outer surfaces of the outer trans
`parent substrates 3a and 3c so that the polarization axes
`to a two-color display for selectively displaying a black
`color image or a blue color image thereon. Further
`thereof cross each other at an angle of 30'.
`When respective values are set as described above,
`more, by switching over from such a state that the
`the aforementioned inequalities (l) to (4) are satis?ed.
`predetermined voltage is applied to the whole area of
`Particularly, when the inequality (4) is satis?ed, the ON
`the liquid crystal layer 6b of the second cell layer 2
`or OFF voltage is selectively applied to the liquid crys
`corresponding to all the pixels to such a state that no
`tal layer 60 of the ?rst cell layer 1 under the condition
`voltage is applied only to a partial area of the liquid
`that the predetermined voltage is applied to the liquid
`crystal layer 6b corresponding to any selected group of
`crystal layer 6b of the second cell layer 2 so as to display
`pixels with use of a simple multiplex driving method, a
`two-color image composed of black and blue color
`a monochromatic image on the double-layered-type
`liquid crystal device. On the other hand, the ON or
`images is displayed on the selected group of pixels in
`OFF voltage is selectively applied to the liquid crystal
`such a state that a monochromatic display composed of
`layer 60 of the ?rst cell layer 1 under the condition that
`white and black color images is displayed on the other
`no voltage is applied to the liquid crystal layer 6b of the
`groups of pixels, resulting in that a multicolor display on
`the whole surface of the double-layered-type liquid
`second cell layer 2 so as to display a multicolor image
`crystal device.
`thereon based on interference colors.
`First of all, a method for driving the double-layered
`type liquid crystal device so as to display a monochro
`matic image and the action thereof will be described
`below with reference to FIG. 50.
`Under the condition that a predetermined voltage
`applied to the liquid crystal layer 617 of the second cell
`layer 2, an ON voltage of about 2.0 V or an OFF volt
`age of about 2.2 V is selectively applied between the
`transparent electrode ?lms 4a and 4b of the ?rst cell
`layer 1. Then, the light having passed through the ?rst
`and second cell layers 1 and 2 passes through the polar
`izer 8b when the OFF voltage is applied to the liquid
`crystal layer 60. On the other hand, the light having
`passed therethrough is shaded by the polarizer 8b when
`the ON_voltage is applied thereto.
`'
`Namely, as shown in FIG. 5a, the red color light R,
`the green color light G and the blue color light B pass
`through each partial area of the polarizer 8b corre
`sponding to each of a ?rst group of pixels of the liquid
`crystal layer 60 to which the OFF voltage is applied,
`and then, a white color image is displayed on each of
`the ?rst group of pixels. On the other hand, the red
`color light R, the green color light G and the blue color
`light B are shaded by each partial area of the polarizer
`8b corresponding to each of a second group of pixels of
`the liquid crystal layer 60 to which the ON voltage is
`
`Second Preferred Embodiment
`FIG. 5a and 5b are graphs of characteristic curves
`showing the relation between a voltage applied to a
`liquid crystal layer 60 of a ?rst cell layer 1 and a light
`transmittance in a double-layered-type liquid crystal
`device of a second preferred embodiment according to
`the present invention, wherein FIG. 5a shows the char
`acteristics in the case of a monochromatic display, and
`FIG. 5b shows the characteristics in the case of a multi
`color display. The double-layered-type liquid crystal
`device of the second preferred embodiment has a struc
`ture similar to that of the ?rst preferred embodiment.
`Therefore, the composition of the double-layered-type
`liquid crystal device of the second preferred embodi
`ment will be described below with reference to FIG. 1.
`In this double-layered~type liquid crystal device,
`transparent substrates 3a to 3c are made of glass. After
`?lms of ITO having a thickness of about 1500 A are
`deposited on the inner surface of the transparent sub
`strate 3a, both the surfaces of the transparent substrate
`3b and the inner surface of the transparent substrate 3c
`by the vapor deposition method, they are etched so as
`to have desirable patterns, resulting in transparent elec
`trical conductive electrode ?lms 4a to 4d formed
`thereon. On each of the transparent el