Liquid crystal display device

Abstract: Several large-screen displays making use of liquid crystal light valve (5) have been realized. The photoactivated liquid crystal light valve (5) is composed by intervening a photo­ conductor layer (25) between a liquid crystal layer (26) and an electrode (21b). The photoconductor layer (25) is changed in its impedance when exposed with light. Therefore, when light is emitted to the photoconductor layer (25) while a voltage is applied between electrodes (21a, 21b), the voltage applied to the exposed portion varies, and the orientation state of the liquid crystal layer (26) changes, and an image is formed on the liquid crystal layer (26). The structure for emitting/­ interrupting the light mentioned above may be reduced in size by using liquid crystal shutter arrays (3, 4). As the liquid crystal layer (26) to be used in the liquid crystal shutter arrays (3, 4), SmC* phase liquid crystal showing a ferro­ dielectric property may be used, so that the response may be enhanced. Therefore, not limited to the still picture display alone, a moving picture may be also displayed. Still more, since the liquid crystal shutter arrays (3, 4) are statically driven, the control is easy, and the number of electrodes (21a, 21b) may be increased, so that the image of high resolution may be displayed on the liquid crystal display valve (5).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device for displaying by projecting an image held by image holding means on a screen. 2. Description of the Prior Art Fig. 1 is a diagram showing an optical composition of a first prior art of a liquid crystal display using a light crystal light valve 5 possessing a photoconductor layer. When displaying an image on the liquid crystal display device, the image displayed in a cathode ray tube (CRT) 51 is entered into the liquid crystal light valve 5 by way of a lens 52. Fig. 7 is a sectional view showing the composition of a liquid crystal light valve 5. In the composition of the liquid crystal light valve 5, transparent electrodes 22a, 22b composed of indium oxide-tin oxide transparent conductive film (ITO) are formed on glass substrates 21a, 21b, and a hydrogenated amorphous silicon (a-Si:H) is formed on the transparent electrode 22b as photoconductor layer 25. The hydrogenated amorphous silicon is made of silane gas and hydrogen gas, and is fabricated by employing the plasma CVD method. On its surface, a multilayer film of silicon/silicon oxide is formed by sputtering method as dielectric mirror 24. After forming polyimide films by spin coating as orientation films 23a, 23b, the molecular orientation is processed by rubbing, and the glass substrates 21a, 21b are glued together by way of a spacer 27. By injecting and sealing a mixed nematic liquid crystal containing chiral material as liquid crystal layer 26, the liquid crystal light valve 5 is composed. As the operation mode of the liquid crystal light valve 5, the hybrid field effect is employed. Between the transparent electrodes 22a, 22b of the liquid crystal light valve 5 composed in such structure, a voltage is applied from an AC power source 28. When the image from the CRT 51 is entered from the glass substrate 21b side as mentioned above, the impedance of the photoconductor layer 25 varies depending on the quantity of incident light. As a result, the voltage to be applied to the liquid crystal layer 26 is changed, and the orientation state of the liquid crystal is modified, so that an image corresponding to the image from the CRT 51 is formed on the liquid crystal layer 26. When light from a light source 54 enters the liquid crystal light valve 5 in which the image is thus formed, by way of a lens 55 and a polarization beam splitter 56, this incident light is reflected by the dielectric mirror 24, and the portion of this light reflected after passing through the orientation changed part of the liquid crystal layer 26 is changed in the polarization direction by the electro-optical effect, so that it can pass through the polarization beam splitter 56. This reflected light is magnified by a lens 57, so that the image formed on the liquid crystal light valve 5 is projected on the screen 58. Fig. 2 is a diagram showing an optical structure of a liquid crystal display device in a second prior art. This second prior art is similar to the first prior art, and the corresponding parts are identified with same reference numbers. In the second prior art, an image is formed on the liquid crystal light valve 5 by means of a laser beam 59. In the first prior art, since the resolution of the image displayed by the liquid crystal display device is determined by the resolution of the CRT 51, it is difficult to enhance the resolution. Besides, since it is necessary to incorporate the CRT 51 into the liquid crystal display device, it is difficult to downsize the liquid crystal display device. In the second prior art, although the resolution may be improved by reducing the irradiation area of the laser beam, the space for accommodating the laser beam control mechanism is needed, and hence it is difficult to downsize the liquid crystal display device. Liquid crystal display devices having the features of the preamble of appended claim 1 are known from the US patents 4,082,430 and 4,699,498. These documents disclose a further arrangement for writing an image into an image storing liquid crystal cell. This arrangement is a shutter liquid crystal cell means comprising crossing electrodes which are driven by a shutter driving means for selectively transmitting light from a light source to the rear side of the image storing liquid crystal cell where the photoconductor layer is provided. In both prior art cases, the shutter liquid crystal cell means is a single liquid crystal cell having crossing electrodes. However, in the device of the first mentioned US patent, the image storing liquid crystal cell and the shutter liquid crystal cell are stapled one above the other, whereas in the device of the second mentioned US patent these two cells are arranged independently from each other, with several optical devices in between. SUMMARY OF THE INVENTION It is the object of the invention to provide a liquid crystal display device comprising an image holding liquid crystal cell and an arrangement for writing an image into said cell, which device has high resolution and a small sized writing arrangement. The liquid crystal display device of the invention is defined by the teaching of appended claim 1. Preferably, each of said two liquid crystal cells comprises band-shaped electrodes on each of the two substrates of the cell, said band-shaped electrodes running parallel at mutual intervals in respectively corresponding positions. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects of the invention, as well as the features and advantages thereof, will be better understood and appreciated in the following detailed description taken in conjunction with the drawings, in which: Fig. 1 is a block diagram for explaining the first prior art, Fig. 2 is a block diagram for explaining the second prior art, Fig. 3 is a diagram showing an optical structure of a liquid crystal display device 1, Fig 4 is a block diagram showing an electrical structure of the liquid crystal display device 1, Fig. 5 is a perspective view of a liquid crystal shutter array 3, Fig. 6 is a sectional view of the liquid crystal shutter array 3, and Fig. 7 is a sectional view of a liquid crystal light valve 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, one of the preferred embodiments of the invention is described in detail below. Fig. 3 is a diagram showing an optical composition of a liquid crystal display device 1 as one of the embodiments of the invention. The light from a light source 2 is selectively passed or interrupted by selective passing means 17, and a writing light L1 corresponding to the image to be displayed is formed. The selective transmitting means 17 is composed of liquid crystal shutter arrays 3, 4 which are liquid crystal elements. The lighting light L1 is applied to a liquid crystal light valve 5 which is image holding means, and the corresponding image is displayed in the liquid crystal light valve 5. When projecting the image displayed in the liquid crystal light valve 5 on a screen 10, the light from a light source for reading 6 is focused by a lens 7, and is linearly polarized by a polarization beam splitter 8 which is polarization optical means, and is entered in the liquid crystal light valve 5. In the liquid crystal light valve 5, a light reflection layer is formed as described later, and the light entering the liquid crystal light valve 5 is reflected by the light reflection layer and is entered again in the polarization beam splitter 8. Of the light reflected by the light reflection layer, the portion passing through the liquid crystal layer part where the image is displayed, that is, the orientation changed part of the liquid crystal is changed in the polarization direction by the electro-optical effect of the liquid crystal, so that it can pass through the polarization beam splitter 8. The transmitted light is magnified by a lens 9, and is emitted to the screen 10. As a result, the image displayed in the liquid crystal light valve 5 is projected on the screen 10. Fig. 4 is a block diagram for explaining the driving method of the liquid crystal shutter arrays 3, 4, and Fig. 5 is a magnified oblique view showing part of the structure of the liquid crystal shutter array 3. In the liquid crystal shutter array 3, a plurality of band-shaped transparent electrodes 43a, 43b are formed on the mutually confronting surfaces of a pair of transparent electrodes 42a, 42b, parallel at mutual intervals in the respectively corresponding positions. The liquid crystal shutter array 4 is similarly composed, and these liquid crystal shutter arrays 3 and 4 are disposed so that the band-shaped electrodes may cross each other orthogonally. The image information from image input means 11 is given to a control unit 13 by way of an interface circuit 12. The control unit 13 stores the image information in a display buffer 14, and, according to this image information, drives the liquid crystal shutter arrays 3, 4 statically by way of driving circuits 15, 16. For example, a voltage is applied between a set of electrodes 43a, 43b of the liquid crystal shutter array 3 to transmit the light from the light source 2, and a voltage is applied between the electrodes 43a and 43b of the liquid crystal shutter array 4 as many as necessary, so that the light necessary for displaying the image information may be entered in the liquid crystal light valve 5. By repeating such action, the light corresponding to the image information may be entered in the liquid crystal light valve 5 in line sequence. Fig. 6 is a sectional view of the liquid crystal shutter array 3. On the mutually confronting surfaces of the transparent substrates 42a, 42b made of glass, acryl or the like, electrodes 43a, 43b composed of indium oxide-tin oxide transparent conductive films (ITO) are formed in a band shape, and orientation films 44a, 44b are formed thereon. As the orientation films 44a, 44b, inorganic films such as silicon oxide (SiO) and silicon dioxide (SiO₂), or polyimide, polyvinyl alcohol, acryl and other organic films may be used. The orientation films 44a, 44b are treated with molecular orientation by rubbing. Such transparent substrates 42a, 42b are glued together with a spacer 45 at a spacing of 2 micron. Between the substrates is injected and sealed a liquid crystal layer 46, which is a liquid crystal showing SmC* phase (C-layer of smectic liquid crystal containing chiral material) as represented by CS-1014 of Chisso Corporation. Afterwards, the liquid crystal in the cell is once transformed into isostropic liquid, and is then gradually cooled to SmC* phase. Polarizers 41a, 41b are disposed on surfaces which are opposite to liquid crystal layer 46 of transparent substrates 42a, 42b respectively. As a result, the liquid crystal optical shutter array 3 making use of the SmC* phase liquid crystal having a ferrodielectric property is prepared. The structure of the liquid crystal shutter array 4 same as that of the liquid crystal shutter array 3. Fig. 7 is a sectional view of the liquid crystal light valve 5. Indium oxide-tin oxide transparent conductive films (ITO) are formed on the glass substrates 21a, 21b as transparent electrodes 22a, 22b. A hydrogenated amorphous silicon (a-Si:H) is formed on the transparent electrode 22b as photoconductor layer 25. The hydrogenated amorphous silicon was made of silane gas and hydrogen gas and prepared by plasma CVD method. A multilayer film of silicon/silicon oxide is formed thereon by sputtering method as a dielectric mirror 24 which is a light reflection layer. After forming polyimide films by spin coating as orientation films 23a, 23b, molecular orientation is treated by rubbing, and glass substrates 21a, 21b are glued together by way of a spacer 27. As liquid crystal layer 26, a mixed nematic liquid crystal containing chiral material is injected and sealed. Thus, the liquid crystal light valve 5 is prepared. As the operation mode of the liquid crystal light valve 5, the hybrid field effect is employed. Between the transparent electrodes 22a, 22b of the liquid crystal light valve 5 in such structure, a voltage is applied from the AC power source 28. When writing light L1 enters from the glass substrate 21b side, the impedance of the photoconductor layer 25 varies depending on the quantity of incident light. As a result, the voltage applied to the liquid crystal layer 26 is changed, and the orientation state of the liquid crystal varies, and an image is formed in the liquid crystal layer 26. Therefore, the light entering from the glass substrate 22a side is reflected by the dielectric mirror 24, and only the light running through the liquid crystal layer 26 changed in the orientation state is changed in the polarization direction, so that it can pass through the polarization beam splitter 8 as stated above. According to this embodiment, therefore, by using the liquid crystal shutter arrays 3, 4, the size of the liquid crystal display device 1 may be reduced. Besides, by using the liquid crystal shutter arrays 3, 4 making use of the SmC* phase liquid crystal showing a ferrodielectric property, the response of the liquid crystal shutter arrays 3, 4 may be enhanced. Therefore, if the image to be written is a moving picture, a quantity of light necessary for displaying the image in the liquid crystal light valve 5 may be sufficiently given. Besides, since the liquid crystal shutter arrays 3, 4 are statically driven, the control is easy. Therefore, the number of electrodes 43a, 43b may be increased, and the image of high resolution may be displayed in the liquid crystal light valve 5. Meanwhile, as the liquid crystal of liquid crystal shutter arrays 3, 4, a mixed nematic liquid crystal with a double refractive index of nearly 0.13 may be also used. Furthermore, two-frequency driven LCD, pi-cell and other high speed responsive nematic LCD may be used. As the photoconductor layer 25 used in the liquid crystal light valve 5, cadmium sulfide (CdS), hydrogenated amorphous silicon (a-Si:H), hydrogenated silicon amorphous carbide (a-SiC:H), and others may be also used. Incidentally, the photoconductor layer 25 may be composed also in a Schottky structure. In this case, when hydrogenated amorphous silicon is used in the photoconductor layer 25, instead of the transparent electrode 22b, a semitransparent electrode made of, for example, palladium (Pd), platinum (Pt) and molybdenum (Mo) is formed. The semitransparent electrode is formed in a thickness of about 50 Å by, for example, vacuum deposition method. When a crystalline silicon is used in the phtoconductor layer 25, gold (Au), palladium (Pd) or platinum (Pt) is used in the semitransparent electrode. When a crystalline gallium arsenic is used in the photoconductor layer 25, gold (Au) or platinum (Pt) is used in the semitransparent electrode. As the operation mode of the liquid crystal light valve 5 and liquid crystal shutter arrays 3, 4, when using smectic liquid crystal, birefringence mode, guest-host mode or light scattering mode may be employed. Where nematic liquid crystal is used, the twisted nematic mode, electric field induced birefringence mode, dynamic scattering mode, or hybrid field effect mode may be employed. The invention may be embodied in other specific forms without departing from the essential characteristics thereof, as defined by the appended claims.

Claims: A liquid crystal display device comprising: an image holding liquid crystal cell (5) comprising: -- a front side substrate (21a) and a rear side substrate (21b) with a liquid crystal layer (26) between these substrates, -- electrodes (22a, 22b) on each of said two substrates of the cell at respectively corresponding portions, -- a photoconductor layer (25) on the electrodes (22b) on the rear side substrate (21b) and -- a mirror (24) on said photoconductor layer; a light source (2); and a shutter liquid crystal cell means (17) comprising crossing electrodes which are driven by a shutter driving means for selectively transmitting light images from said light source to the rear side of said image holding liquid crystal cell; characterized in that said shutter liquid crystal cell means (17) comprises two liquid crystal cells (3, 4) which are arranged one behind the other in the direction of the light path from the light source towards said image holding liquid crystal cell. A device according to claim 1, wherein each of said liquid crystal cells (3, 4) within said shutter liquid crystal cell means (17) comprises stripe-shaped electrodes (43a, 43b) on each of the two substrates of the cell, said stripe-shaped electrodes running parallel at mutual intervals in respectively corresponding positions. A device according to one of the preceding claims, comprising: a second light source (6) for transmitting light for reading the image stored by said image holding liquid crystal cell; a screen (10) for displaying said image; and an optical means (7, 8, 9) for directing light from said second light source towards the front side of said image holding liquid crystal cell, and for transmitting the light reflected at said mirror (24) of said image holding liquid crystal cell to said screen. A device according to claim 3, wherein said optical means (7, 8, 9) comprises a polarization optical means (8) for reflecting incident light from said second light source (6) of a predetermined polarization characteristic and for transmitting incident light from said image holding liquid crystal cell (5) of a second predetermined polarization characteristic.

Inventors: HATANO AKITSUGU, ISHII YUTAKA, HATANO, AKITSUGU, ISHII, YUTAKA
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1989
Main classification: G02F1
IPC codes: G03B21, G02B5, G02F1, G09F9