JPH0822021A - Spatial light modulator and liquid crystal display device - Google Patents

Abstract

(57) [Summary] [Objective] A photoconductor (105) having a current rectifying property and at least one liquid crystal layer selected from a liquid crystal layer (118) having an antiferroelectric phase as a phase state of liquid crystal are paired. Transparent electrode (1
(02,114) has a structure that is sandwiched between
(EN) Provided are a spatial light modulator and a liquid crystal display device, which have a wide viewing angle and high-speed responsiveness, can reproduce a moving image including an intermediate tone display, and are stable and highly reliable. [Structure] A liquid crystal layer (118) having an antiferroelectric phase as a phase state with a photoconductor (115) having a current rectifying property is sandwiched between a pair of transparent electrodes (102, 114) to serve as a spatial light modulator (117). In the meantime, the voltage period in which the liquid crystal layer applies a voltage higher than the voltage required for the phase transition from the antiferroelectric phase to the ferroelectric phase in the opposite direction to the rectifying characteristics of the photoconductor, and A unit period is constituted and driven from a voltage period in which a voltage equal to or higher than the voltage required for the phase transition to the dielectric phase is applied in a polarity in the forward direction with respect to the rectifying characteristics of the photoconductor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spatial light modulator and a liquid crystal display device used for displaying moving images and still images, which are applied to projection televisions for displaying moving images of large screen and high brightness.

[0002]

2. Description of the Related Art As a liquid crystal display element using a liquid crystal material, a nematic liquid crystal display element has been put into practical use and has produced various products. However, the response speed of nematic liquid crystals is slow,
Speeding up for improving display quality has been taken up as an issue. Ferroelectric liquid crystal (hereinafter F
(Referred to as LC) has a spontaneous polarization, so that it is possible to realize a large response speed of several tens of microseconds or less by applying a voltage. Further, as a display method, it has been found that a bistable state is realized by enclosing a ferroelectric liquid crystal in a thickness sufficiently narrower than a pitch length of twist alignment of several tens of μm (Clark et al .: Appl. Phys.Let., 36,899 (1980)
, JP-A-56-107216, U.S. Pat. No. 4,367,924). This method is called a surface stabilization mode, and it has been found that a liquid crystal display device using the surface stabilization mode newly realizes a memory function in addition to a high-speed response characteristic. With this memory function, display of a two-dimensional image has come to be realized by an element having a simple electrode structure and a simple driving method. However, since the display value of each pixel is a binary display of black and white corresponding to the two stable alignment states of the ferroelectric liquid crystal, it should be applied to a halftone display element such as a television image. Was difficult. Therefore, there have been proposed methods for pseudo multi-gradation display by methods such as area gradation in which pixels are finely divided and driven, or a method such as time division driving, but satisfactory display quality has not been realized yet.

On the other hand, a display device using an antiferroelectric liquid crystal (hereinafter referred to as ALC) has been developed in place of FLC (Chandani et al .: Jpn.J.Appl.Phy).
s., 27, L729 (1988)). This element is a display element that utilizes switching between the above three states of a stable antiferroelectric phase and two ferroelectric phases that are induced by an electric field. The antiferroelectric phase-ferroelectric phase transition has a steep threshold with respect to the magnitude of the applied voltage. Further, the optical characteristics of the element with respect to the applied voltage have a hysteresis characteristic and have a memory function of holding each of the three states. This ALC will be
It is expected as a liquid crystal display material that realizes high-speed response and multi-valued display.

By the way, in recent years, there has been an increasing demand for realization of a moving image display device which realizes a large screen, high density, high resolution and high brightness. In order to realize it, either of the conventional method using a cathode ray tube and the method using a liquid crystal display element is effective. The former is a projection method using a projection tube of a cathode ray tube, but it has a problem that it is difficult to achieve both high density, high resolution and high brightness. That is, in order to obtain a high-resolution image, it is necessary to narrow down the electron beam to suppress the brightness. On the other hand, in the latter liquid crystal display device, a projection method is mainly used by using an element in which a thin film transistor and a liquid crystal are combined. This system has the same technical problem as in the former case that the aperture ratio is lowered and the brightness is lowered when trying to realize high density and high resolution. A method combining the advantages of both has been proposed by Hughes (Japanese Patent Laid-Open No. 53-137165). Although this has low brightness, a high-resolution moving image of a cathode ray tube is given to the spatial light modulator as light input information, and high-brightness read light is applied to the liquid crystal layer to be modulated, thereby optical amplification. It is a method of obtaining a converted output image. In order to realize further high-speed response, we have proposed a spatial light modulator using FLC in the liquid crystal layer and a liquid crystal display device using the same. Also, a method of displaying halftones, which has been considered to be difficult in the past, has been found by optical writing using FLC. The projection system has an advantage that an image with high light utilization efficiency can be produced by utilizing the wide viewing angle characteristic of FLC. Further F
By combining the high-speed response characteristics of LC with a new halftone display method, it has become possible to faithfully reproduce a moving image in which the light input is given by a cathode ray tube including the halftone.

[0005]

By the way, in principle,
The FLC has a spontaneous polarization and controls halftone modulation according to the amount of charges held by electrodes sandwiching the liquid crystal layer. Therefore, there is a problem in that the FLC responds sensitively to changes in the retained charges. For this reason, it is necessary to suppress the accumulation of extra charges as much as possible. FLC also has the drawback that the orientation is easily disturbed by a mechanical shock from the outside.

In order to solve the above-mentioned conventional problems, the present invention maintains a wide viewing angle and high-speed response in a spatial light modulator comprising a photoconductor and a liquid crystal layer, and provides a halftone to an optical input of a moving image. An object of the present invention is to provide a spatial light modulation element that can be reproduced including a display and is stable and highly reliable, and a liquid crystal display device using the spatial light modulation element that can be miniaturized.

[0007]

To achieve the above object, the spatial light modulator of the present invention is selected from a photoconductor having a current rectifying property and a liquid crystal layer having an antiferroelectric phase as a liquid crystal phase state. At least one liquid crystal layer is provided so as to be sandwiched between a pair of transparent electrodes. In the above description, the liquid crystal layer having an antiferroelectric phase may be a liquid crystal containing an antiferroelectric phase as a main component or a liquid crystal layer having a mixed phase of an antiferroelectric phase and a ferroelectric phase.

In the above structure, the liquid crystal layer having the antiferroelectric phase is in the antiferroelectric phase state when the applied voltage is a low voltage up to a certain voltage, and the voltage value of the higher applied voltage is In a high voltage region equal to or higher than the threshold value (V _th (H)), the liquid crystal phase undergoes a phase transition to the ferroelectric phase, the voltage is reduced from the state of the ferroelectric phase, and the lower threshold voltage value (V _th (L))
It is preferable that the liquid crystal layer undergoes a phase transition from the ferroelectric phase to the antiferroelectric phase and returns, and the same phenomenon occurs when the change reverses the polarity of the applied voltage.

Further, in the above structure, it is preferable that a plurality of minute metal thin films electrically independent of each other be provided between the photoconductor and the liquid crystal layer. Further, in the above structure, a groove is formed in a part of the photoconductor between the minute metal thin films,
It is preferable to have a metal thin film on the bottom thereof.

Further, in the above structure, it is preferable that a groove portion is provided in a part of the photoconductor between the minute metal thin films, and a metal thin film whose bottom is covered with an insulating film. Further, in the above structure, it is preferable that a part of the groove portion of the photoconductor between the minute metal thin films has an eave portion in which the metal thin film projects between the pixels.

Further, in the above structure, it is preferable that the photoconductor and the liquid crystal layer have a dielectric reflection layer formed of a multi-layered film of thin films having different dielectric constants. Moreover, in the said structure, it is preferable to arrange | position the polarizer and the analyzer orthogonally.

Further, in the above structure, a first period in which a voltage higher than a threshold value V _th (H) for applying a phase transition from the antiferroelectric phase to the ferroelectric phase is applied, and the ferroelectric phase to the antiferroelectric phase are applied. A second period in which a voltage equal to or lower than a threshold value V _th (L) necessary for returning to a phase is applied, and white display is performed in the first period and black display is performed in the second period. preferable.

In the above structure, it is preferable that the voltage is applied by light irradiation. Further, in the above configuration,
When the photoconductor of the spatial light modulator is irradiated with light, the voltage applied to the liquid crystal layer during the voltage period applied in the polarity opposite to the rectifying characteristics of the photoconductor changes from the antiferroelectric phase to the ferroelectric. It is preferable to provide a means for giving light intensity and a light input which is equal to or higher than a predetermined voltage required for phase transition.

In the above structure, the unit cycle of the voltage applied between the transparent electrodes is a predetermined voltage or more required for the liquid crystal layer to undergo a phase transition from the antiferroelectric phase to the ferroelectric phase. The write voltage period applied in the opposite polarity with respect to the polarity of the photoconductor and the voltage higher than the predetermined voltage required for the liquid crystal layer to undergo the phase transition from the ferroelectric phase to the antiferroelectric phase It is preferable that the erasing voltage period is applied with the following polarity.

In the above structure, it is preferable that the photoconductor having a current rectifying property is an amorphous silicon (a-Si: H) layer. In the above structure, the amorphous silicon (a-Si: H) is the i-type a with boron added.
It is preferably a —Si: H layer.

Next, the liquid crystal display device of the present invention has a structure in which a photoconductor having a current rectifying property and a liquid crystal layer having an antiferroelectric phase as a liquid crystal phase state are sandwiched between a pair of transparent electrodes. At least a spatial light modulation element provided, a display element for optically inputting into the photoconductor, and a power supply for applying a driving voltage to the spatial light modulation element are provided.

In the above structure, it is preferable that the spatial light modulator includes a light input means in which the frequency of the drive voltage is equal to or higher than the display frequency of the display element. Further, in the above structure, it is preferable that the display element for inputting light is at least one display element selected from a liquid crystal display element driven by a thin film transistor and a cathode ray tube display element.

Further, in the above-mentioned structure, the liquid crystal layer of the spatial light modulator is irradiated with the incident light linearly deflected through the polarizing plate deflected in a fixed direction, and the reflected light from the spatial light modulator is polarized. It is preferable to arrange the polarizing plate so that the liquid crystal alignment state that gives the minimum reflected light intensity is the antiferroelectric phase when reading is performed through the polarizing plate whose deflection direction is orthogonal to the plate.

Further, in the above structure, the ratio of the ferroelectric phase of the mixed phase of the antiferroelectric phase and the ferroelectric phase increases with the increase of the intensity of the light irradiating the photoconductor, so that the gradation It is preferable that a means for displaying is provided.

Further, in the above construction, the television moving image from the cathode ray tube is reduced as light information through the lens to illuminate it within the effective area of the spatial light modulator, while the light from the reading light source is condensed by the condenser lens. Means for irradiating the deflected beam splitter via the deflected beam splitter, linearly deflected by the deflected beam splitter to the spatial light modulator, and irradiating the modulated reflected light with a projection lens to form an image on a screen. Is preferably provided.

[0021]

According to the structure of the liquid crystal display device of the present invention described above, the photoconductor having the current rectifying property and the liquid crystal layer having the antiferroelectric phase as the phase state of the liquid crystal are sandwiched between the pair of transparent electrodes. Due to the existing structure, a wide viewing angle and high-speed response can be maintained, and it is possible to reproduce the moving image including the halftone display, and a stable and highly reliable spatial light modulator. Can be realized. In the above description, the liquid crystal layer having an antiferroelectric phase may be a liquid crystal containing an antiferroelectric phase as a main component or a liquid crystal layer having a mixed phase of an antiferroelectric phase and a ferroelectric phase.

Further, between the transparent electrodes of the spatial light modulator, a voltage equal to or higher than the voltage required for the liquid crystal to make a phase transition from the antiferroelectric phase to the ferroelectric phase is applied in a polarity opposite to the rectifying characteristics of the photoconductor. A unit cycle is composed of the write voltage period for which the liquid crystal layer is applied and the erase voltage period in which a voltage equal to or higher than the voltage required for the phase transition from the ferroelectric phase to the antiferroelectric phase is applied in the forward direction with respect to the rectifying characteristics of the photoconductor. And drive.

The voltage applied to the liquid crystal layer is inversely strong during the period in which the photoconductor of the spatial light modulator is irradiated with light and the voltage is applied in a polarity opposite to the rectifying characteristics of the photoconductor. It gives a light intensity higher than the voltage required for the phase transition from the dielectric phase to the ferroelectric phase.

Further, incident light linearly deflected through a polarizing plate deflected in a fixed direction is applied to a spatial light modulating element, and reflected light from the spatial light modulating element is deflected in a direction orthogonal to the polarizing plate. When reading through the arranged polarizing plate, the polarizing plate is arranged so that the alignment state of the liquid crystal that gives the minimum reflected light intensity is the antiferroelectric phase.

Further, when a photoconductor having a current rectifying property and a liquid crystal layer having an antiferroelectric phase as a phase state are sandwiched between a pair of transparent electrodes to form a spatial light modulator, halftone display is performed by an optical writing method. The following three items are used to obtain a moving image (light modulation principle, halftone display principle, moving image display principle).
I will explain separately. (1) Light Modulation Principle A typical example of a change in the light intensity of linearly polarized light passing through the liquid crystal layer, which is modulated by the liquid crystal and output, with respect to the voltage applied to the antiferroelectric liquid crystal layer is shown in FIG. It was shown to. The output light has a history with respect to the applied voltage. In FIG. 3, when the applied voltage is a low voltage from 0 V to 17 V, it is in an antiferroelectric phase state, but the applied voltage has a certain threshold value (V
_In the high voltage region of _th (H), 17 V in the example of FIG. 3) or more, the liquid crystal phase undergoes a phase transition to a ferroelectric phase. Next, when the voltage is reduced, the phase transitions from the ferroelectric phase to the antiferroelectric phase at the lower threshold voltage value (V _th (L), 6 V or less in FIG. 3). This change also occurs when the polarity of the applied voltage is reversed.

Here, the polarizer and the analyzer are arranged so as to be orthogonal to each other so as to provide output light having the lowest antiferroelectric phase state. That is, black display is performed in the antiferroelectric phase state at a low applied voltage, and white display is performed in the ferroelectric phase state at a high applied voltage. Since the antiferroelectric phase state is arranged so as to cancel the spontaneous polarization of each molecule in the layer, it becomes a stable coordination with respect to charge fluctuations near the electrodes. Therefore, when the antiferroelectric phase is used for black display, high contrast display can be obtained. By the way, the change of the output light becomes symmetric with respect to the polarity of the applied voltage, and the three stable displays (b′-ab, cd and c′-d in FIG. 3) are displayed.
3 ').

The antiferroelectric liquid crystal shown in FIG.
Driving is performed by applying pressure. One cycle is strongly induced from the antiferroelectric phase
Threshold V for phase transition to electric phase_th(H) or higher
The first period of applying pressure and from the ferroelectric phase to the antiferroelectric phase
Threshold value V required for returning _th(L) Apply voltage below
It consists of the second period. As the history characteristic shows
White display during the first period and black display during the second period.
It Therefore, as shown in FIG. 5, white display is performed according to the change in voltage value.
And black display appear alternately.

Next, the photoconductor 105 having the rectifying characteristics shown in FIG. 1 or 2 and the antiferroelectric liquid crystal layer 118 described above.
The output in the case of irradiating the photoconductor with light while applying the drive voltage of FIG. 4 to the element having a laminated structure will be described. During the first applied voltage period, the voltage is applied in the direction opposite to the rectification characteristic. At this time, an equivalent circuit of the spatial light modulator of FIG. 1 is shown in FIG. The applied voltage equal to or higher than V _th (H) is divided into the voltage V _a applied to the photoconductor and the voltage V _f applied to the antiferroelectric liquid crystal layer. Upon irradiation with light, charges are generated and a photocurrent I _ph flows, resulting in _a decrease in V a and an increase in V _f . In the second applied voltage period, as can be seen from the rectification characteristics of the photoconductor shown in the example of FIG. 7, a large current flows regardless of light irradiation, and as a result, V _f increases. FIG. 8 shows the time variation of V _f and output light when the light intensity is changed under the condition of constant light irradiation. Without light irradiation (Fig. 8 (a)
), V _f becomes V _th (H) or less in the first applied voltage period, and the antiferroelectric phase is maintained to always display black. When light is irradiated, the light intensity increases (Fig. 8 (b), (c), (d)
) In the first applied voltage period, light absorption increases the charges generated in the photoconductor, and V _f increases accordingly. Then, when V _f becomes V _th (H) or more, a phase transition occurs in the liquid crystal, and the ferroelectric phase is displayed in white. During the second applied voltage period, V _f becomes V _th (L) or more regardless of the light irradiation intensity, and the liquid crystal returns to the antiferroelectric phase to display black. (2) Halftone Display Principle The timing at which a phase transition occurs in the first applied voltage period differs depending on the intensity of light emitted. That is, when the intensity of light irradiation increases, V _f becomes faster than V _{th in} the first period.
When (H) is reached and the threshold value is exceeded, the liquid crystal starts to undergo phase transition. When the driving unit cycle is set to a shorter time with respect to the change in the intensity of light irradiation, the display is the time average of the white display time of the first period and the black display time of the second period. Therefore, as the irradiation light intensity increases, the output light intensity increases as a result of the time averaging. This action enables halftone display. Next, consider the case of a liquid crystal layer having a mixed phase of an antiferroelectric phase and a ferroelectric phase as the phase state of the liquid crystal. The threshold value changes depending on the mixing ratio of this mixed phase. That is, an increase in the ratio of antiferroelectric phase results in an increase in V _th (H). Therefore, it is possible to create a characteristic that smoothly rises with respect to the light irradiation light. (3) Video display principle The optical information input to the spatial light modulator is 16.7 m per screen.
It is assumed that this image is written in the element by a moving image displayed by a television signal of sec. When one cycle of the applied voltage is configured to be 1 msec as shown in FIG. 9A, one screen repeats about 17 times of optical writing and second erasing in the first period. For example, when an image is written by a cathode ray tube, the time change of each point of the image is as shown in FIG. 9B due to the emission characteristics of the phosphor, whereas the output light of the spatial light modulator receives the emission of this phosphor. Is reproduced as shown in FIG. 9 (c).

[0029]

The present invention will be described more specifically with reference to the following examples. 1 and 2 show an embodiment in which a photoconductor having a current rectifying property and a liquid crystal layer having an antiferroelectric phase as a phase state are sandwiched between a pair of transparent electrodes to form a spatial light modulator.

FIG. 1 shows an example of a structure in which a plurality of minute pixel reflection films (metal thin films) 108 electrically independent from each other are provided between the photoconductor 105 and the liquid crystal layer 118. A typical example of the photoconductor 105 having a rectifying property is amorphous silicon containing hydrogen (hereinafter referred to as a-Si: H). The preferable thickness of the photoconductor 105 is about 0.2 to 10 μm. Further, between the p-type a-Si: H layer 104 and the liquid crystal layer 118, the i-type a-Si: H layer (photoconductor) 105 and n are formed.
A type a-Si: H layer 106 is formed, and a p-type a-Si: H layer 104, an i-type a-Si: H layer (photoconductor) 105 and n are formed.
Three layers of the type a-Si: H layer 106 are continuously laminated to form a photoconductor having a diode structure.

The photoconductor 105 is divided for each pixel, and the pixel reflection film 108 of each metal thin film functions simultaneously with the pixel electrode 107 as a reflection film for reflecting the read light. An output light-shielding film (metal thin film) 109 made of a metal thin film is provided on the bottom between the pixels, and further 30% by weight of carbon black is used.
Dispersed polymer (polymethylmethacrylate) film 110
It has a groove structure filled with. This groove structure prevents the charges from diffusing between the pixels and also prevents the read light irradiated between the pixels from leaking to the photoconductor and malfunctioning. Below the photoconductor 105 is an input light-shielding film 103 for separating light input information into each pixel. In order to align the antiferroelectric liquid crystal, the liquid crystal layer is sandwiched by the polymer alignment films 111 and 113 which are aligned in the same direction by the rubbing method.
Considering that the optimum thickness of the liquid crystal layer is the reflection mode,
From the refractive index of the liquid crystal, it is determined to be half the optical path length required under the condition that the maximum modulation rate is obtained. By dispersing the spacers 112 having the same particle diameter as the optimum film thickness, the liquid crystal film thickness is secured. As the spacer 112, for example, silicon oxide can be used. The average diameter of the spacers 112 (that is, the liquid crystal film thickness) is preferably about 0.5 to 8 μm.

A voltage 116 as shown in the example of FIG. 4 is applied to the transparent conductive films (transparent electrodes) 102 and 114 formed on the respective surfaces of the pair of transparent insulating substrates 101 and 115, that is, the surfaces in contact with the liquid crystal layer 118. The element 117 is driven to drive the element 117.

Other materials used for the photoconductive layer include, for example, CdS, CdTe, CdSe, ZnS, ZnSe,
Compound semiconductors such as GaAs, GaN, GaP, GaAlAs, InP, amorphous semiconductors such as Se, SeTe, AsSe, Si, Ge, Si _1-x C _x , Si _1-x Ge _x , G
e _1-x C _x (0 <x <1) polycrystalline or amorphous semiconductor, and (1) phthalocyanine pigment (hereinafter abbreviated as “Pc”), for example, metal-free Pc, XPc (X = Cu, Ni) ，
Co, TiO, Mg, Si (OH) _2, etc.), AlClP
cCl, TiOClPcCl, InClPcCl, In
ClPc, InBrPcBr, etc. (2) Azo dyes such as monoazo dyes, disazo dyes, etc. (3) Penylene pigments such as penylene acid anhydride and penenylene imide,
(4) indigoid dye, (5) quinacridone pigment,
(6) Polycyclic quinones such as anthraquinones and pyrenequinones, (7) cyanine dyes, (8) xanthene dyes,
(9) A charge transfer complex such as PVK / TNF, (10) a eutectic complex formed from a pyrylium salt dye and a polycarbonate resin, and (11) an organic semiconductor such as an azurenium salt compound.

Amorphous Si (hereinafter a-Si),
Amorphous Ge (hereinafter a-Ge), amorphous Si _1-x C
_x (hereinafter a-Si _1-x C _x ), amorphous Si _1-x Ge
_x (hereinafter a-Si _1-x Ge _x ), amorphous Ge _1-x C
_{When x} (hereinafter a-Ge _1-x C _x ) is used in the photoconductive layer, it is also preferable to include hydrogen or a halogen element, and oxygen or halogen is included for the purpose of decreasing the dielectric constant and increasing the resistivity. It is also preferable to include nitrogen. In order to control the resistivity, elements such as B, Al, and Ga, which are p-type impurities, or P, As, which are n-type impurities, are added.
It is also preferable to add an element such as Sb. In this way, the amorphous materials doped with impurities are stacked to form p / n type, p / n type
By forming a junction of i-type, i / n-type, p / i / n-type, etc. and forming a depletion layer in the photoconductive layer, it is possible to control the dielectric constant and dark resistance or operating voltage polarity. is there. Further, not only an amorphous material but also a depletion layer may be formed in the photoconductive layer by stacking two or more kinds of the above materials to form a heterojunction.

FIG. 2 shows an example of a structure having a thin multi-layer film 202 having different dielectric constants between a photoconductor and a liquid crystal layer. The dielectric multilayer film 202 is designed to reflect the visible light reading light. A small amount of leaked light that passes through the dielectric multilayer film 202 of the read light is absorbed by the light shielding film 201 so as not to enter the photoconductor 105.

Specific examples will be described below. Example 1 FIG. 10 shows a spatial light modulator having the structure shown in FIG.
It was manufactured by the process shown in. (1) Optically polished glass substrate 101 (55 mm x
An indium-tin oxide alloy (hereinafter referred to as ITO) having a thickness of 100 nm was formed as a transparent conductive film 102 on a surface of 65 mm × 1.1 mm by a sputtering method. (2) Chromium (hereinafter Cr
Was formed by a 200 nm electron beam evaporation method, and then an input light shielding film 103 having a width of 3.0 μm was formed by using a general photolithography technique. (3) Next, plasma CVD (chemical vapor deposite)
P-type a-S containing 100 ppm of boron added by the method
i: H layer 104 (film thickness 50 nm), i-type a-S without addition
i: H layer 105 (photoconductor) (film thickness 1.7 μm) and n-type a-Si: H layer 106 containing 1000 ppm of phosphorus.
Three layers (thickness 300 nm) were successively laminated to form a photoconductor having a diode structure. (4) Cr is vapor-deposited again on the entire surface to a thickness of 200 nm and deposited to 23.5 μ.
2000 x 2000 squares of m square with a pitch of 25 μm
(4 million pieces in total) were produced by lithography. Each C
The r thin film 107 corresponds to a pixel, and the effective area is 50 mm × 5
It is 0 mm. The input light-shielding film 103 is just the Cr pixel electrode 1
It was designed to be located between 07. Here, the Cr film thickness is 2
The range was 0 to 500 nm. (5) Next, by a reactive ion etching method using a mixed gas of CF ₄ and oxygen, the a-Si: H layer between pixels was removed by 0.5 μm in the vertical direction by using the Cr pixel as an etching mask. Later, it can be isotropically etched C
A chemical dry etching method using a mixed gas of F ₄ oxygen was performed to remove 1.0 μm in the horizontal direction to form a groove having an eaves (collar) between Cr pixels. At least the n-type a-Si: H layer between the pixels is removed by the groove portion, and it is possible to prevent the leakage of charges between the adjacent pixels. Depending on the etching conditions, this groove structure can be produced only by etching. (6) Aluminum (hereinafter referred to as Al) was deposited on the entire surface in the range of 20 to 300 nm by the electron beam evaporation method. The Al film on the Cr pixel is the pixel reflection film 108 having a high reflectance.
Became. On the other hand, the Al film formed on the bottom of the groove portion became the output light-shielding film 109 for preventing the light from being read out from between the pixels and being incident on the photoconductor.

Cr: 150 nm and Al: 150 n
By continuously forming m, Al of the output light-shielding film 109 is formed.
Can also be prevented from diffusing into the a-Si: H layer located thereunder. (7) Next, a polymer film having carbon particles dispersed therein was applied in a thickness of 2 μm. In this step, the groove is filled with the polymer film and the pixel surface is also covered. The polymer film was uniformly removed over the entire surface by a reactive ion etching method using oxygen, and the etching was terminated when Al of the pixel appeared on the surface again. As a result, the polymer film 11 is formed only in the groove portion between the pixels.
Zeros are filled. This part is not covered with the light-shielding film by absorbing the light incident between the pixels a-Si: H
Prevents reading light from entering the layer. Further, the polymer film between pixels serves as a black matrix at the time of display, suppresses the reflected light from between pixels to be low, and also has a role of always displaying black. (8) A polyimide film having a thickness of 50 nm was formed as the alignment film 111. Similarly, a polyimide film 113 having a thickness of 50 nm was formed on the glass substrate 115 with the ITO 114, which was the opposite substrate. Then, a nylon cloth was wound around a dedicated roller for both substrates, and the rollers were rotated while pressing the cloth against the substrates for rubbing treatment. The rubbing directions of both substrates were the same. Next, spacers 112 made of silicon oxide having a particle diameter of 1.5 μm were dispersed on one of the substrates to control the liquid crystal film thickness. A liquid crystal cell was made by screen-printing a sealing resin around the other substrate and bonding the two substrates together. (9) After installing the liquid crystal cell in a vacuum device and reducing the pressure, 120
Antiferroelectric liquid crystal (CS-400 manufactured by Chisso)
0) was injected into the cell by capillarity.

FIG. 11 shows the time response characteristic of the reflected light when the intensity of the optical writing light applied to the photoconductor of the spatial light modulator 117 is changed. Driving is performed with a forward voltage of +10 V for erasing, a second application time of 0.1 msec and a reverse voltage of -20 V for optical writing, and a first application time of 1.1.
It was set to msec. Therefore, the driving frequency was 833 Hz.

When the polarizing direction of the polarizer is set so as to coincide with the rubbing direction, black display is obtained in the antiferroelectric phase state. When the optical writing light intensity was changed from 0 to 0.8 mW / cm ² , the reflected light intensity increased due to the increase in the intensity.

When the output light is defined by the time average of the reflected light intensity, the change of the output light with respect to the optical writing light intensity is as shown in FIG. This is a halftone display in which the reflectance is controlled from 0% to 80% by changing the optical writing light intensity from 0 to 0.8 mW / cm ² .

The maximum reflectance is 80% because the maximum voltage applied during optical writing is 20 V and the time required for the phase transition at this electric field strength is 0.3 msec. During the period of 1.1 msec, this transition time is a loss for displaying white. The maximum contrast ratio was 200 or more.

A projection television system was constructed using the spatial light modulator 117. A conceptual diagram of the system is shown in FIG. Since a television moving image with a frame frequency of 60 Hz is incident as optical information, for example, a cathode ray tube 301 (hereinafter referred to as a CRT) having a diagonal size of 7 inches is used to reduce the size through a lens 302 and a spatial light modulator 117 having a size of 5 cm × 5 cm. Illuminated within the effective area of. The CRT phosphor has an afterglow time of about 10 msec, and aS
i: Green phosphor P1 that matches well with the high-sensitivity wavelength region of the H layer
I chose. Metal halide lamp 303 for reading light source
(250 W, luminous efficiency 70 lm / W) was used, and the condenser lens 304 was used to set the spatial light modulator 117 so as to have uniform and high brightness. The spatial light modulator 117 was irradiated with the read light linearly deflected by the deflecting beam splitter 305, and the modulated reflected light was enlarged by the projection lens 306 and focused on the screen 307. A 70-inch diagonal enlarged image was displayed on the screen.
A green dichroic filter was installed immediately after the light source 303 together with infrared and ultraviolet cut filters, and a deflecting beam splitter 305 whose characteristics correspond to green was used. A light flux of 250 lm reached the screen 307, and the light utilization efficiency was 1 lm / W. The contrast ratio on the screen was over 100: 1.
The displayed moving image had no afterimage, and a good halftone display was obtained.

A projection system using a liquid crystal element driven by a thin film transistor as an optical writing means instead of the CRT 301 was manufactured. Since the aperture ratio of this liquid crystal element is 30%, the brightness on the screen is lower than that in CRT writing, but the system is downsized.

Example 2 A spatial light modulator 203 having the structure shown in FIG. 2 was manufactured by the following method. A glass substrate 101 (55 mm × 65) that has been optically polished in the same manner as in Example 1
(mm × 1.1 mm) surface with ITO as a transparent conductive film
The transparent conductive film 102 is formed to a thickness of 100 nm by the sputtering method.
It was formed into a film. Next, boron 1 is added by the plasma CVD method.
P-type a-Si: H layer 104 added with 00 ppm (film thickness 5
0 nm), an i-type a-Si: H layer 105 (thickness 1.7 μm) without addition, and an n-type a-Si: H layer 106 (thickness 300 nm) containing 1000 ppm of phosphorus are continuously formed. And laminated to form a photoconductor having a diode structure.

On this film, a CdSe layer of the light shielding layer 201 was formed to a thickness of 500 nm by vapor deposition. The CdSe layer absorbs visible light. Subsequently, a dielectric multilayer film 202 was formed by stacking a titanium oxide layer and a silicon oxide layer by a sputtering method. The reflection spectrum is 99.9 for wavelengths including green.
It had a reflectance of at least%. A polyimide film having a thickness of 50 nm is formed as an alignment film 111 on the dielectric film as in the first embodiment.
A film was formed.

Then, a liquid crystal cell was assembled in the same manner as in Example 1 to fabricate a spatial light modulator 203 having an antiferroelectric liquid crystal. This spatial light modulator was installed in the projection television system used in Example 1 to output a moving image.

A light flux of 250 lm reached the screen, and the light utilization efficiency was 1 lm / W. The contrast ratio on the screen was over 100: 1.

[0048]

As described above, according to the present invention, in a spatial light modulator comprising a photoconductor and a liquid crystal layer, a wide viewing angle and a high speed response are maintained, and a halftone is applied to an optical input of a moving image. I was able to reproduce it including the display. In addition, a stable and highly reliable element could be provided. The optical writing projection TV using this element has a large screen, light brightness, high resolution,
A high contrast image display could be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a spatial light modulator according to an embodiment of the present invention.

FIG. 2 is a sectional view schematically showing a spatial light modulator according to an embodiment of the present invention.

FIG. 3 is a hysteresis characteristic diagram of reflectance with respect to an applied voltage of the same antiferroelectric liquid crystal.

FIG. 4 is a reflection characteristic diagram of the antiferroelectric liquid crystal with respect to the same asymmetric applied pulse voltage.

FIG. 5 is a diagram showing changes with time in the asymmetric applied pulse voltage and the reflectance of the antiferroelectric liquid crystal.

FIG. 6 is an equivalent circuit diagram of the spatial light modulator of one embodiment of the present invention.

FIG. 7 is a rectification characteristic diagram of an a-Si: H photoconductor according to an embodiment of the present invention.

FIG. 8 is a diagram showing changes with time in voltage applied to the liquid crystal layer and reflectance in this example.

FIG. 9 is a diagram showing an optical writing method for displaying a moving image according to an embodiment of the present invention.

FIG. 10 is a manufacturing process diagram of a spatial light modulator according to an embodiment of the present invention.

FIG. 11 is a time response characteristic diagram of reflected light when the optical writing light intensity of the spatial light modulator according to the embodiment of the present invention is changed.

FIG. 12 is a diagram showing a change in output light in time average of reflected light intensity with respect to optical writing light intensity in one embodiment of the present invention.

FIG. 13 is a diagram showing a projection television system using a spatial light modulator according to an embodiment of the present invention.

[Explanation of symbols]

 101 transparent insulating substrate 102 transparent conductive film (transparent electrode) 103 input light-shielding film 104 p-type a-Si: H film 105 i-type a-Si: H film (photoconductor) 106 n-type a-Si: H film 107 Pixel electrode 108 Pixel reflective film (metal thin film) 109 Output light-shielding film (metal thin film) 110 Polymer film 111 Alignment film 112 Spacer 113 Alignment film 114 Transparent conductive film (transparent electrode) 115 Transparent insulating substrate 116 Drive voltage 117 Spatial light modulation Element 118 Liquid crystal layer 201 Light shielding layer 202 Dielectric multilayer film 203 Spatial light modulation element 301 Cathode ray tube (CRT) 302 Lens 303 Light source metal halide lamp 304 Condenser lens 305 Deflection beam splitter 306 Projection lens 307 Screen

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G09G 3/18

Claims (20)

[Claims] 1. A structure in which a photoconductor having a current rectifying property and at least one liquid crystal layer selected from a liquid crystal layer having an antiferroelectric phase as a liquid crystal phase state are sandwiched between a pair of transparent electrodes. Spatial light modulator equipped. 2. A threshold value of a voltage value of a liquid crystal layer having an antiferroelectric phase, which is in an antiferroelectric phase when the applied voltage is a low voltage up to a certain voltage and the applied voltage is higher. (V _th
In the high voltage region above (H), the liquid crystal phase undergoes a phase transition to the ferroelectric phase, the voltage is reduced from the state of the ferroelectric phase, and at the lower threshold voltage value (V _th (L)), The spatial light modulator according to claim 1, wherein the spatial light modulator is a liquid crystal layer that undergoes a phase transition from a ferroelectric phase to an antiferroelectric phase and returns, and the change also occurs when the polarity of an applied voltage is reversed. 3. A spatial light modulator according to claim 1, wherein a plurality of minute metal thin films electrically independent of each other are provided between the photoconductor and the liquid crystal layer. 4. The spatial light modulator according to claim 3, wherein a groove is provided in a part of the photoconductor between the minute metal thin films, and the metal thin film is provided at the bottom thereof. 5. The spatial light modulator according to claim 4, wherein a groove is provided in a part of the photoconductor between the minute metal thin films, and the metal thin film has a bottom covered with an insulating film. 6. The spatial light modulator according to claim 3, wherein a part of the groove portion of the photoconductor between the minute metal thin films has an eave portion in which the metal thin film is projected between the pixels. 7. The spatial light modulator according to claim 1, further comprising a dielectric reflection layer formed of a multi-layered thin film having different dielectric constants between the photoconductor and the liquid crystal layer. 8. The spatial light modulator according to claim 1, wherein the polarizer and the analyzer are arranged orthogonally to each other. 9. A first period of applying a voltage equal to or higher than a threshold value V _th (H) for causing a phase transition from an antiferroelectric phase to a ferroelectric phase, and returning from the ferroelectric phase to the antiferroelectric phase. 3. A second period in which a voltage equal to or lower than a threshold value V _th (L) necessary for the application is applied, white display is performed in the first period, and black display is performed in the second period. Spatial light modulator. 10. The spatial light modulator according to claim 2, wherein the voltage is applied by light irradiation. 11. When the photoconductor of the spatial light modulator is irradiated with light, the voltage applied to the liquid crystal layer during the voltage period applied in a polarity opposite to the rectifying characteristic of the photoconductor is anti-strong. 11. The spatial light modulator according to claim 10, further comprising means for giving a light intensity that gives a light intensity equal to or higher than a predetermined voltage required for the phase transition from the dielectric phase to the ferroelectric phase and inputting the light. 12. A unit cycle of a voltage applied between the transparent electrodes is a voltage higher than a predetermined voltage required for the liquid crystal layer to undergo a phase transition from an antiferroelectric phase to a ferroelectric phase with respect to the rectifying characteristic of the photoconductor. Direction applied to the photoconductor, and a voltage equal to or higher than the predetermined voltage required for the liquid crystal layer to make a phase transition from the ferroelectric phase to the antiferroelectric phase is set to the polarity that is in the forward direction with respect to the rectifying characteristics of the photoconductor. The spatial light modulator according to claim 2, wherein the spatial light modulator comprises an applied erase voltage period. 13. The spatial light modulator according to claim 1, wherein the photoconductor having a current rectifying property is an amorphous silicon (a-Si: H) layer. 14. Amorphous silicon (a-Si: H)
14. The i-type a-Si: H layer added with boron.
The spatial light modulator according to. 15. A spatial light modulator having a structure in which a photoconductor having a current rectifying property and a liquid crystal layer having an antiferroelectric phase as a liquid crystal phase state are sandwiched between a pair of transparent electrodes. A liquid crystal display device comprising at least a display element for optically inputting to the photoconductor and a power supply for applying a driving voltage to the spatial light modulation element. 16. The liquid crystal display device according to claim 15, further comprising an optical input unit in which the frequency of the drive voltage of the spatial light modulator is equal to or higher than the display frequency of the display element. 17. The liquid crystal display device according to claim 15, wherein the display element for inputting light is at least one display element selected from a liquid crystal display element driven by a thin film transistor and a cathode ray tube display element. 18. The liquid crystal display device according to claim 15, further comprising irradiating the liquid crystal layer of the spatial light modulator with incident light linearly polarized through a polarizing plate polarized in a fixed direction, When the reflected light from the modulation element is read out through a polarizing plate whose deflection direction is arranged in a direction orthogonal to the polarizing plate,
A liquid crystal display device in which a polarizing plate is arranged so that the liquid crystal alignment state that gives the minimum reflected light intensity is in the antiferroelectric phase. 19. The liquid crystal display device according to claim 15, further comprising a ferroelectric phase of a mixed phase of an antiferroelectric phase and a ferroelectric phase as the intensity of light applied to the photoconductor increases. A liquid crystal display device provided with means for displaying gradation by increasing the ratio. 20. The liquid crystal display device according to claim 15, wherein the television moving image from the cathode ray tube is illuminated as optical information through the lens into the effective area of the spatial light modulation element, while the light source is read out. Irradiating the polarized light to the deflecting beam splitter through the condenser lens, irradiating the reading light linearly deflected by the deflecting beam splitter to the spatial light modulation element, and enlarging the modulated reflected light with the projection lens to screen. A liquid crystal display device having means for forming an image on the top.