JPH0321927A - Optical writing type liquid crystal light valve - Google Patents

Abstract

PURPOSE:To allow optical writing by forming Schottky barrier on the joint surface with a photoconductive film between an optical writing side transparent electrode and the photoconductive film. CONSTITUTION:The transparent electrode 3a, a barrier metallic film 13, the photoconductive layer 4, a light shielding film 5, a dielectric mirror 6, and a liquid crystal oriented film 7a are formed on the inner side of a transparent substrate 2a on the side where image writing is executed. The photoconductive layer 4 exhibits a large resistivity by the Schottky barrier in a reverse bias state and exhibits the smaller resistivity in a forward bias state. The part irradiated with light changes to the sate of the low reflectivity in the reflectivity characteristic of the reverse bias state and the part not irradiated with the light maintains the state of the high reflectivity when the photoconductive layer is irradiated with the writing light. The writing of image information is thereby enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an intermediate storage medium for an optical printer and an image display device.
Hikari Shasota. This invention relates to an optical writing type liquid crystal light valve using ferroelectric liquid crystal that is applied to image processing devices, optical information processing systems, etc.

[Part 1 of the Invention: The present invention is. A highly sensitive photoconductive layer that exhibits high resistivity in the dark and high conductivity when illuminated with light. This relates to the structure of the photoconductive layer of an optical writing type liquid crystal light valve that combines a highly transparent liquid crystal with bistable memory properties.On the transparent electrode on the optical writing side,
It has a structure in which a photoconductive layer consisting of an i-layer of hydrogenated amorphous silicon is placed on top of the barrier metal thin film layer.
A Schottky barrier diode is formed by a metal-semiconductor junction. It exhibits extremely high resistivity when reverse voltage is applied in the dark. When a forward voltage is applied, the resistivity is lower than when a reverse voltage is applied. A photoconductive film having the above structure,
By combining this with a ferroelectric liquid crystal that has bistable memory properties, we have created an optically writable liquid crystal light valve that is capable of optical writing using direct current drive and that can erase images in memory at high speed.

[Conventional technology] Optical writing type liquid crystal light valves have traditionally been used for adrenosing methods and the display mode of the liquid crystal used. Various studies are being carried out. Among others. Twisted nematic mode.
A liquid crystal light valve that combines a voltage-controlled birefringence mode and a photoconductive film. It has characteristics close to practical levels, and has been used in incoherent-coherent converters for optical information processing, etc. However, in these modes, there is no memorability of the written image, and the image disappears when the writing light is removed. Even when writing digitally with a beam spot such as a laser beam, the image retention time of the written part is short, so it is not possible to increase the resolution. When trying to obtain a high resolution large screen display. It is necessary to overwrite the exact same location over and over again at high speed, which requires the development of an ultra-high-speed, ultra-high-precision laser scanner and an ultra-sensitive photoconductive film, which is extremely difficult to achieve. That's a thing. A combination of cholesteric-nematic phase transition mode and photoconductive film has memory properties, but
It had the disadvantages of slow writing speed and low contrast. In recent years, we have focused on ferroelectric liquid crystals, which have the potential to discover excellent properties such as high-speed response, memory performance, high contrast, and wide field of view, and have developed an optical writing system that combines ferroelectric liquid crystals and photoconductive films. type liquid crystal light valves have been actively researched.

[Problem to be solved by the invention] In a conventional optical writing type liquid crystal light valve that combines a photoconductive film and a ferroelectric liquid crystal, the resistivity of the photoconductive film and the ferroelectric liquid crystal layer in the dark is almost the same value. , and the applied DC voltage is . It is applied at the same rate to the photoconductive film and the ferroelectric liquid crystal layer. This makes it difficult to perform optical writing using the bistable memory of ferroelectric liquid crystals at a certain threshold. Furthermore, in conventional photoconductive films, even if the polarity of the applied DC voltage changes, the resistivity value remains almost the same, so when erasing an image that has been optically written into memory. It is necessary to apply a considerably high voltage with reverse polarity, which is disadvantageous in practice.

[Means for solving the problem] To solve the above problem. The present invention is. Between the transparent electrode on the optical writing side and the photoconductive film. A thin film of metallic material was provided to form a Shosotky barrier at the interface with the photoconductive film.

The Shosotokhi barrier is created by applying a DC voltage in the opposite direction in dark and dark conditions. It exhibits a higher resistivity than a ferroelectric liquid crystal layer, enabling optical writing using bistable memory, and also exhibits a lower resistivity than a ferroelectric liquid crystal layer when DC voltage is applied in the forward direction. Images stored in optically written memory can be easily erased.

[Function] The liquid crystal light valve of the present invention is manufactured by applying a forward DC bias voltage that is sufficiently higher than the threshold voltage in the dark to a photoconductive film exhibiting Schottky barrier diode characteristics. are aligned to a stable state in one direction, and that state is stored in memory. After going through this first step. In the dark, it is below the threshold voltage. At the time of light irradiation, the voltage exceeds the threshold voltage. Image writing is performed in a second step in which optical writing is performed using a laser beam or the like while applying a DC bias voltage of opposite polarity. Photocarriers are generated in the photoconductive layer in the area irradiated with light, and the generated carriers drift in the direction of the electric field due to the DC bias voltage, resulting in a decrease in the resistance of the photoconductive layer. A voltage of opposite polarity that is higher than the threshold voltage is applied to the region that has been irradiated with light, and the liquid crystal molecules are reversed due to the reversal of spontaneous polarization, and the region is memorized in the other stable state. The image formed in this way is irradiated with linearly polarized projection light whose polarization axis is aligned with the alignment direction (or perpendicular direction) of the liquid crystal molecules aligned in the first step, and the polarization of the reflected light by the reflective layer. It can be read out on a screen by projection through an analyzer arranged so that the polarization axis is perpendicular (or parallel) to the direction.

[Example] Figure 1 is. 1 is a cross-sectional view showing the structure of a liquid crystal light valve according to the present invention. The present invention will be explained below using figures.

A transparent electrode (3a), a barrier metal film (13), etc. are provided on the inside of the transparent substrate (2a) on the side on which image writing is performed by an optical writing means (1) such as a laser beam, an LED, or a CRT. Photoconductive layer (4), light shielding film (5). A dielectric layer (6) and a liquid crystal alignment film (7a) are formed, and a counter transparent electrode (3b) and a liquid crystal are formed inside the transparent substrate (2b) on the side reflected and projected by the projection light (8). An alignment film (7b) is formed.These pair of transparent substrates are overlapped by a peripheral seal (9) containing a substrate such as glass fiber.
A ferroelectric liquid crystal (10) is sealed in the gap.

According to the liquid crystal light valve as described above, writing is performed on the ferroelectric liquid crystal layer (10) by the writing light 1 from the outer surface, and the written optical information is read out by the projection light.
It is projected onto the screen (12). FIG. 2 is a characteristic diagram showing the resistivity value versus bias voltage of the photoconductive layer according to the present invention. In the reverse bias state, it exhibits a large resistivity due to the Schottky barrier, and in the forward bias state, it exhibits a smaller resistivity. Figure 3 shows that using the optical writing type liquid crystal light valve formed in this way, the optical writing side is darkened and! This shows the voltage-light reflectance characteristics when a voltage is applied between the electrodes. Under reverse bias conditions, the resistivity of the photoconductive layer is greater than that of the ferroelectric liquid crystal. Most of the applied voltage is applied to the photoconductive layer. In the forward bias state. The resistivity of the photoconductive layer is lower than that of the ferroelectric liquid crystal, and most of the applied voltage is applied to the liquid crystal layer. FIG. 4 shows the voltage-light reflectance characteristics when a voltage is applied between the electrodes while irradiating the entire surface with light from the optical writing side. In this case, the entire surface of the photoconductive layer is in a low resistance state, and most of the applied voltage is applied to the ferroelectric liquid crystal. Therefore, in the optically writable liquid crystal light valve of the present invention, it is possible to keep the directors of liquid crystal molecules aligned uniformly over the entire surface with a low applied voltage in the forward bias state shown in FIG.
This is possible in the dark, and even if a large applied voltage is applied by changing the applied voltage to the reverse bias state shown in FIG. 3, the alignment of the directors of the liquid crystal molecules is maintained and the reflectance remains high. In this state, when the writing light is irradiated, the part irradiated with the light changes to a state with low reflectance according to the reflectance characteristics in the reverse bias state shown in Figure 4, and the part not irradiated with the light reflects. By keeping the rate high, image information can be written. In the example, first, glass substrates with a thickness of 2 mm and polished to 1/4 lambda or less on both sides are prepared as the transparent substrates 2a and 2b.
ITO transparent electrodes with a thickness of 500A were formed as transparent electrodes 3a and 3b. A thin Pt film is formed as a barrier metal film 13 on the optical writing side transparent electrode layer 3a. p
t thin film. Although it is formed by vacuum evaporation, a film thickness of 50 angstroms is selected because the light transmittance decreases if the thickness is too high. On top of that, a gas mainly composed of SiH4 was decomposed by discharge to form a 4 um thick layer of intrinsically hydrogenated amorphous silicon to form photoconductive N4. On the photoconductive layer thus formed, 15 layers of Si and Ge were laminated to form a dielectric layer 6 as a light reflecting film. On the dielectric mirror 6 and the transparent substrate 3b on the projection side, silicon monoxide (Si◯) was deposited at an angle of 82 degrees to the normal direction of the substrate and in the normal direction of vapor deposition to a film thickness of 2000 angstroms. The liquid crystal alignment layers 7a and 7b were formed by oblique vapor deposition to a thickness of .Transparent substrate 2
a, 2b are. The alignment layers 7a and 7b are made to face each other. Diameter 1
．． Adhesion is controlled by Sun+, and the ferroelectric liquid crystal bottom is
A ferroelectric liquid crystal MIF2 is obtained by adding an optically active substance to an ester-based Smectisoc C liquid crystal mixture. In addition, in this practical example, pt is used as the material for the barrier metal film 13, but Ir, Au, Pd, Rh
Even when the barrier metal film l3 is formed using metals such as , Ni, Cr, etc., the same results as when using PT are obtained. Next, the liquid crystal light valve of the present invention is made incoherent. An example of application as a coherent converter will be explained. Figure 5 is. 1 is a conceptual diagram of a coherent optical correlation system using a liquid crystal optical element according to the present invention.

The reflected light from the measurement object 19 is . An image is formed by the lens 20 onto the liquid crystal light valve 2l according to the present invention. Here, since the liquid crystal optical element according to the present invention has a larger area than one using a nonlinear optical crystal, it can be used even if the object to be measured is large. Since the response speed is faster than that using a liquid crystal in a mode such as DSM, high-speed processing close to real time is possible. LCD light bulb 21
In the image that occurred. Coherent light 2 is split into linearly polarized light by a polarization beam splinter 22, and its polarization axis direction matches the direct direction of the ferroelectric liquid crystal molecules at the time of complete erasure.
3 is irradiated. The irradiated light undergoes polarization state conversion due to birefringence and is reflected only at the portion where the director is reversed due to writing. The reflected light passes through the polarization beam subsoter 22 again, and the intensity of the portion where the polarization state has been changed by birefringence is inevitably lowered, so that the intensity of the part where the polarization state has been changed by birefringence is reduced, and the intensity of the part where the polarization state has been changed by birefringence is reduced.
3, by using the polarizing beam splitter 22 to form an image on the correlation coordinate plane 27 through the polarization beam splitter 22, which does not enter the liquid crystal light valve 2l, and through the lens 24, mated filter 25, and lens 26. It performs optical information processing. In this application example, incoherence is achieved by the liquid crystal optical element of the present invention. By using a coherent transducer, it can be used for large objects. and,
A coherent optical correlation system capable of high-speed processing close to real time is realized [Effects of the invention] As described above, the optically written ferroelectric system using the Schottky barrier diode type photoconductive layer of the present invention is realized. Regarding liquid crystal light valves. A large-area, high-speed incoherent device that can perform optical writing under DC bias and erase the written image at low voltage. It can be applied to coherent converters, rewritable and erasable optical bistable memories, etc. in particular. The range of applications of optical printers to intermediate storage media, image display devices, optical shutters, image processing devices, optical information processing systems, etc. can be dramatically expanded.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of an optically writable liquid crystal light valve according to the present invention, FIG. 2 is a characteristic diagram showing the resistivity value with respect to bias voltage of the photoconductive layer according to the present invention, and FIG.
Figure 4 is a voltage-light reflectance characteristic diagram of the optically writable liquid crystal light valve of the present invention when driven by DC bias voltage in the dark. A voltage-light reflectance characteristic diagram of the optically writable liquid crystal light valve of the present invention driven by DC bias voltage during light irradiation. Fifth
The figure is a conceptual diagram of a coherent system using the liquid crystal light valve of the present invention. 1... Optical writing means, 'la,'lb... Transparent substrate, 3
a, 3b...transparent electrode, 4...photoconductive layer, 5...light shielding film. 6...Dielectric mirror,? a, 7b...Liquid crystal alignment film, 8
...Projection light, 9..Outer seal, 10..Ferroelectric liquid crystal, 11..Anti-reflection film. l2...Screen, 13...
Barrier metal film.

Claims (2)

[Claims] (1) A writing means using light such as a laser beam, LED, or halogen light, a photoconductive layer, a light reflection layer, a liquid crystal alignment layer,
A ferroelectric liquid crystal has a structure in which a ferroelectric liquid crystal is sandwiched between a pair of transparent electrode substrates on which a voltage applying means is formed, and the ferroelectric liquid crystal has a bistable memory property between light reflectance and applied voltage. An optically writable liquid crystal light valve characterized in that a barrier metal thin film forming a Schottky barrier is formed between a transparent electrode on the optical writing side and the photoconductive layer. (2) The photoconductive layer is i-type hydrogenated amorphous silicon, and the barrier metal thin film material is Pt, Ir,
2. The optically writable liquid crystal light valve according to claim 1, characterized in that it is a thin metal film of Au, Pd, Rh, Ni, Cr, or the like.