JPH06110078A - Photoconduction type liquid crystal light valve - Google Patents

Abstract

PURPOSE:To obtain excellent resolution and make an output pattern uniform. CONSTITUTION:The photoconduction type liquid crystal light valve has a photoconductive layer 3, a dielectric mirror 6, and a liquid crystal layer 9 between transparent electrodes 2 formed on a couple of glass substrates 1 and is provided with plural conductive thin films 4 and a buffer layer 5 formed of an insulating material between the photoconductive layer 3 and dielectric mirror 6; and the buffer layer 5 is formed by using a bias electron cyclotron resonance plasma CVD and the photoconductive layer 3 is formed by using electron cyclotron resonance plasma CVD.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoconductive liquid crystal light valve. More specifically, the present invention relates to a photoconductive liquid crystal light valve used for an image display device, an optical information processing system, and the like, which performs writing and reading by light using the photoconductive effect of a photoconductive layer and the electro-optical effect of a liquid crystal layer.

[0002]

2. Description of the Related Art A photoconductive liquid crystal light valve (hereinafter LCL)
V) has a function of writing two-dimensional information with light and reading the information with other light. Utilizing the property, it is expected to be applied to image display, optical information processing system, and the like. ing. FIG. 3 shows a configuration example of a conventional LCLV. Reference numeral 11 denotes a glass substrate, on which a transparent electrode 12 is formed, and a liquid crystal layer 19 is laminated on the transparent electrode 12 via a photoconductive layer 13, a dielectric mirror 16, a liquid crystal alignment film 17 and a spacer 18. For example, a hydrogenated amorphous silicon film (a-Si: H) is used as the photoconductive layer, and a nematic (Nm) liquid crystal or a ferroelectric liquid crystal (FLC) is used as the liquid crystal material. Reference numeral 20 denotes a power source for driving the LCLV, which is connected to the transparent electrode 12. The operation principle will be described below.

First, an AC voltage is applied to the LCLV from the driving power source 20. In the LCLV, the impedance of the photoconductive layer 13 is set to be sufficiently higher than the impedance of the liquid crystal layer 19 in the state where the writing light 31 is not irradiated, and in this state, the driving voltage is mainly the photoconductive layer 13. Is being applied to. Here, writing light 3
When 1 is irradiated, the impedance of the photoconductive layer in the light-irradiated portion is lowered, a driving voltage is applied to the liquid crystal layer 19 corresponding to that portion, the liquid crystal molecules are aligned, and information is written. Information is read from the direction of the glass substrate 11 through the polarization beam splitter 32.
And the reflected light modulated according to the alignment state of the liquid crystal molecules is detected.

[0004]

LC having such a configuration
The LV has a problem in that, when information is written, carriers are diffused in the lateral direction in the photoconductive layer and the resolution is lowered. As a method to solve this point, for example,
There is one in which an island-shaped metal thin film is provided together with or instead of the dielectric mirror (Japanese Patent Laid-Open No. 3-18829). Since the metal thin film has a high reflectance for visible light,
The writing light is reflected by the metal thin film to cause multiple reflection in the photoconductive layer, which affects the resolution. To prevent this, it is necessary to increase the film thickness of the photoconductive layer or use a material having a small bandgap for the photoconductive layer. LC
The LV has a structure in which many films are stacked as described above, and if there is nonuniformity in the lower film, the upper film is formed to reflect it and the nonuniformity of the layer structure is output. Appears as pattern non-uniformity. Although it is possible to prevent lateral diffusion of carriers in the photoconductive layer by the above method, unevenness (uneven layer structure) due to the provision of the metal thin film exists. However, there is no way to solve even the non-uniformity of the output pattern.

When an a-Si: H film is used as the photoconductive layer, it has been conventionally formed by a plasma CVD method or a reactive sputtering method. The photoconductive layer is usually required to have a film thickness of several μm or more, and when formed by the conventional method, the film formation rate is slow and it takes a very long time to form the photoconductive layer, which is not practical. Attempts have also been made to speed up the film formation, but at that time, there is a problem that powdery SiH ₂ polymer is generated by the secondary reaction of the reactive species and adheres to the substrate surface to cause defects. The rapid production of a photoconductive layer having good characteristics by the method has not been achieved.

[0006]

The present invention was devised in order to solve the above-mentioned problems, and can prevent a decrease in resolution and obtain a uniform output pattern. The present invention provides a photo-writing type liquid crystal light valve which can be formed by solving the problem of film formation at the time of forming a photoconductive layer.

Thus, according to the present invention, there is provided a photoconductive type liquid crystal light valve having a photoconductive layer, a dielectric mirror and a liquid crystal layer between transparent electrodes provided on a pair of transparent substrates, wherein the photoconductive layer is provided. And a plurality of conductive thin films and a buffer layer are provided between the dielectric mirror and the dielectric mirror. Further, according to the present invention, the conductive thin film is a metal thin film or a thin film having crystallinity to which an element of Group III or V of the periodic table is added,
Provided is a photoconductive liquid crystal light valve in which a buffer layer is an insulator material formed by using a bias electron cyclotron resonance plasma CVD method and a photoconductive layer is formed by an amorphous semiconductor formed by using an electron cyclotron resonance plasma CVD method. To be done.

The photoconductive liquid crystal light valve of the present invention can be manufactured, for example, by the following procedure. First, a transparent electrode is formed on a transparent substrate by a vapor deposition method. Examples of the transparent substrate include a glass substrate and the like, and examples of the transparent electrode include indium tin oxide (ITO), tin oxide (SnO ₂ ) and the like, and those in which these are laminated. Furthermore, if necessary, an antireflection film can be provided on the glass substrate facing the transparent electrode. The material used for this antireflection film is Mg
F _{2 and the} like can be mentioned.

Next, a film thickness of 0.1 to 100 μm is formed on the transparent electrode.
To form a photoconductive layer. The film thickness is preferably set within the above range depending on the impedance matching with the liquid crystal material used. The material that can be used for this photoconductive layer is a
-Si, a-SiC, a-SiO, a-SiN and a-
Amorphous semiconductors such as SiGe can be mentioned, and hydrogen or halogen can be contained if necessary. The conductivity can be controlled by adding boron, which is a group III element, to p-type, and adding n-type elements, such as phosphorus and arsenic, which are group V elements. As the photoconductive layer, in addition to i-type, a combination of these i-type, p-type, and n-type semiconductors, such as p / i-type, p / i / p-type, p / i / n-type, etc., has a laminated structure. It is also possible to Further, organic semiconductor materials such as azo pigments, phthalocyanines, and arylamines can be used.

The photoconductor layer can be formed by a plasma CVD method, a sputtering method, an electron cyclotron resonance plasma CVD method (hereinafter referred to as an ECR method), or the like. Of these, the ECR method is preferred. The ECR method is a method of forming a film by generating plasma by utilizing the resonance phenomenon between electrons in a magnetic field and microwaves,
It has the following features.

Conventional electron beam deposition method with high electron energy
Decomposition, excitation, ionization of raw material gas is remarkable compared with the method
Improved to 1 μm / min. High-speed film formation is possible
Relatively low pressure (10^-Five-10^-2Stable with Torr)
Plasma can be generated by the secondary reaction of reactive species.
It is possible to suppress the generation of powdery polymer, and the formed film is a dark film in the case of an a-Si: H film, for example.
Conductivity; 10^-12-10 ^-TenS / cm, photoconductivity; 10^-7
-10^-6cm²/ V shows good characteristics and ECR method
High-speed photoconductive layer with excellent characteristics by using
It is possible to create.

As the film forming apparatus used in the present invention, for example, an apparatus as shown in FIG. 2 can be used. This film forming apparatus has a plasma chamber 44 for generating plasma and a film forming chamber 48 for forming a film, and both chambers are partitioned by a plasma drawing window 46. A magnetic coil 47 is arranged around the plasma chamber 44, and E
A magnetic field that satisfies the conditions of the CR method is generated, and a divergent magnetic field that draws plasma is formed in the film forming chamber 48. Microwaves are introduced into the plasma chamber 44 from the microwave oscillator 41 through the rectangular road wave tube 42 and the quartz microwave introduction window 43. From the gas introduction pipe 52 to the film forming chamber 48, SiH ₄ , SiF ₄ , Si ₂ H ₆ , Si as film forming gas.
Gases such as ₂ F ₆ , CH ₄ , GeH ₄ , PH ₃ and B ₂ H ₆ are introduced. Further, the plasma chamber 44 has a gas introduction pipe 51
A gas such as Ar, H ₂ , He, N ₂ , O ₂ or the like is introduced. Further, in the film forming chamber 48, a substrate holder 50 is arranged, and a substrate 49 such as glass is installed. A high frequency power source 53 is connected to the substrate holder 50 so that a bias can be applied to the substrate. A photoconductive layer made of an amorphous semiconductor can be formed by setting conditions such as a gas for film formation, microwave power, pressure, and substrate temperature using such an apparatus.

Next, a conductive thin film is formed on the photoconductive layer.
This conductive thin film prevents carriers in the photoconductive layer from diffusing in the lateral direction and prevents the resolution from deteriorating. As the conductive thin film that can be used, Al, Au, which has been conventionally used,
Examples include metal thin films such as Mo and Ti, or crystalline thin films such as Si, Ge and SiGe to which B or the like which is an element of Group III of the periodic table or P and As which are elements of a Group V are added. To be In the latter case, since it has sufficient absorption capability for writing light, it is possible to prevent multiple reflection of writing light in the photoconductive layer without increasing the film thickness of the photoconductive layer. As a forming method, a metal thin film can be formed by a vapor deposition method or the like. When a crystalline thin film is used, it can be formed by the same ECR method as that for forming the photoconductive layer. With such a method, the film thickness of 0.01 to
It is deposited to a thickness of 10 μm, and is formed by photolithography and etching so that each size is 10 to 500 μm □.

Next, a buffer layer is formed on the conductive thin film and the photoconductive layer. The buffer layer is made of an insulating material such as SiO _{2 and} is used to uniformly form the dielectric mirror and the liquid crystal layer by eliminating unevenness between the photoconductive layer and the conductive thin film provided on the photoconductive layer. And is formed by a bias electron cyclotron resonance plasma CVD method (hereinafter referred to as a bias ECR method) in which high frequency power is applied to a substrate to form a film. The bias ECR method is described in, for example, J. Vac.Sci.Technol.
B4 (1986) As described in p818, it is a technique to form a flat film on an uneven surface by performing film deposition and sputtering (physical etching) at the same time, and creating a good buffer layer. Is possible.

For film formation by the bias ECR method, first, an EC provided with means for applying electric power to the substrate as shown in FIG.
The glass substrate on which the conductive thin film is formed is placed in the R device. The inside of the apparatus was evacuated to a level of about 10 ⁻⁷ Torr, and a mixed gas of SiH ₄ and O ₂ having a gas flow rate of 0.001 to 1 SLM was introduced into the film forming chamber 48, and the gas flow rate was 0.1 to 100 GHz.
Microwave power of 001-5kW and 0.001 to the substrate
˜100 MHz, 0.001 to 5 kW of high frequency power is applied to form a buffer layer of 0.01 to 10 μm.
When a metal thin film is used as the conductive thin film, first, the buffer layer is formed under the above conditions until the thickness of the buffer layer becomes equal to that of the metal thin film, and in the subsequent process, the gas flow rate is 0.001 to 1 SLM. Inert gas such as Ar gas is introduced to form the buffer layer.

Next, TiO ₂ --Si is formed on the buffer layer.
A dielectric mirror is formed by alternately stacking 10 to 15 layers of O ₂ , MgF—ZnS, Si—SiO _2, etc. by an electron beam evaporation method or the like. The layer thickness of this dielectric mirror layer is 0.01 to 10 μm. Next, a polyimide film or the like is formed on the dielectric mirror by a spin coating method, and orientation is performed by rubbing.

Next, a glass substrate on which a transparent electrode and an alignment film are laminated in the same manner as described above is laminated at a distance of 0.1 to 100 μm so that the alignment films face each other via a spacer, and liquid crystal is sealed between them to form the present invention. It is possible to obtain a photoconductive liquid crystal light valve. Examples of liquid crystal materials that can be used include nematic liquid crystal, smectic A liquid crystal, collective liquid crystal, and ferroelectric liquid crystal.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a structural diagram of an optical writing type liquid crystal light valve according to the present invention. Reference numeral 1 is one glass substrate, and 2 is a transparent electrode provided on the glass substrate. On the transparent electrode 2,
The photoconductive layer 3 for inputting information from the writing light 21, the conductive thin film 4 divided into pixels so as to prevent lateral diffusion of carriers generated in the photoconductive layer 3, and the photoconductive layer 3 are provided on the photoconductive layer 3. A buffer layer 5 for flattening unevenness with the conductive thin film 4, a dielectric mirror 6 for separating the writing light 21 and the reading light 22, and an alignment film 7 for controlling the alignment of the liquid crystal are laminated. On the other glass substrate 1, the transparent electrode 2
And the alignment film 7 are formed so that the alignment films 7 face each other 2
Laminate the glass substrates 1 with a spacer 8 in between,
Liquid crystal 9 is sealed in the meantime. Reference numeral 10 is a power source for driving the optical writing type liquid crystal light valve, which is connected to the transparent electrode 2.

Next, a method of manufacturing the optically writable liquid crystal light valve will be described. First, a glass substrate 1 having a transparent electrode 2 made of a tin-indium oxide film (ITO) / tin oxide (SnO ₂ ) was placed on an ECR device substrate holder 50 as shown in FIG. 2 and placed at 10 ⁻⁷ Torr. The table was evacuated. Next, SiH ₄ gas was introduced into the film forming chamber 48 at 120 SCCM, and Ar gas was introduced at 20 SCCM.
Pressure 1.2 × 10 ^-2 Torr, microwave power 2.5k
A-Si: H which is the photoconductive layer 3 at W (2.45 GHz)
A film was prepared. The film thickness at this time is 7 μm. The glass substrate 1 on which the photoconductive layer 3 has been formed is once taken out from the ECR device, an aluminum thin film (thickness: 1000Å) is vapor-deposited, and patterned by photolithography so that each size is 15 μm □ The metal thin film 4 which is a conductive thin film was formed.

After that, the substrate is set in the ECR apparatus again, and the buffer layer 5 is formed by the bias ECR method. First, as the first stage, the inside of the apparatus was evacuated to the 10 ^-7 Torr level, SiH ₄ and O ₂ were introduced into the film forming chamber 48 at a flow rate of 5 SCCM, and the pressure was 1.5 × 10 ^-3 Tor.
set to rr, microwave power of 600 W is input from the microwave oscillator 41, and high frequency power of 13.56 MHz and 800 W is applied to the substrate from the high frequency power supply 53.
The buffer layer 5 S on the photoconductive layer 3 and the Al electrode 4
The iO ₂ film was laminated until it became equal to the Al electrode. Next, in the second step, the buffer layer 5 is continuously formed in the same manner as in the first step except that Ar is introduced into the plasma chamber 44 from the gas introduction tube 51 at a flow rate of 60 SCCM. Was 0.8 μm.

The reason why Ar is not used in the first stage is that
This is to prevent the Al electrode from being sputtered by Ar. Dielectric thin films of TiO ₂ —SiO ₂ are alternately stacked on the buffer layer by electron beam evaporation to have a layer thickness of 3 μm.
The dielectric mirror 6 was prepared. Further, a polyimide film having a film thickness of 2000 Å was formed thereon as the alignment film 7 by a spin coating method, and an alignment treatment was performed by rubbing.
Next, in the same step as above, the other glass substrate 1 on which the transparent electrode 2 and the alignment film 7 were laminated was bonded via the spacer 8 so that the alignment films 7 face each other, and the liquid crystal 9 was sealed between them. At this time, the liquid crystal used was a phenylcyclohexane nematic liquid crystal, and the cell gap was 6 μm.

Information was written and read by applying a voltage from the voltage applying means 10 to the photo-writing type liquid crystal light valve thus produced. A polarization beam splitter (not shown) is provided on the reading side.
The operation mode was a hybrid field effect mode. The obtained output pattern has excellent contrast, no reduction in resolution was observed, and pattern nonuniformity was also reduced.By providing a buffer layer on multiple metal thin films, the output pattern nonuniformity It was confirmed that the sex could be significantly improved.

Example 2 Next, a method of manufacturing a photoconductive liquid crystal light valve using an n-type microcrystalline silicon film as a photoconductive thin film and an a-Si: H film of p / i structure as a photoconductive layer. I will describe. The basic configuration of the photoconductive type liquid crystal light valve of this embodiment is the same as that of the above-mentioned embodiment 1 shown in FIG.

First, a glass substrate 1 having a transparent electrode 2 made of a tin-indium oxide film (ITO) / tin oxide (SnO ₂ ) is placed on a substrate holder 50 in an ECR apparatus as shown in FIG. The vacuum was evacuated to the level of 10 ^-7 Torr. 1 SCC of SiH ₄ gas in the film forming chamber 48
17 SC of B ₂ H ₆ gas (hydrogen diluted 3000 ppm) at M
Introduced by CM, Ar gas 100S in the plasma chamber 44
It was introduced by CCM, and a p-layer was formed under the conditions of a pressure of 1.0 × 10 ⁻³ Torr and a microwave power of 0.55 kW (frequency 2.45 GHz). The film thickness is 100Å. Here, the supply of microwave power and gas was once stopped, and the inside of the apparatus was evacuated to the 10 ⁻⁷ Torr level again. Next, SiH ₄ gas was introduced into the film forming chamber 48 at 100 SCCM and Ar gas was introduced into the plasma chamber 44 at 20 SCCM, the pressure was 1.2 × 10 ^-2 Torr, and the microwave power was 2.5 kW.
The i layer was created under the condition of (frequency 2.45 GHz). The film thickness is 4 μm. Here, an example of the a-Si: H film to which the impurity element is not added is shown as the i layer,
Besides, it is of course possible to use an a-Si: H film to which a trace amount of boron is added.

Next, a conductive thin film is formed. An n-type microcrystalline silicon film added with phosphorus was used as the conductive thin film used in this example. The formation method was the same ECR method as the method for forming the photoconductive layer. The formation method will be described below. After forming the i-layer of the photoconductive layer, the supply of microwave power and gas was stopped once, and the inside of the apparatus was evacuated to the level of 10 ⁻⁷ Torr. Next, in the film forming chamber 48, SiH ₄ gas was added at 5 SCCM and PH ₃ gas (hydrogen diluted 3000 ppm).
At 85 SCCM and 30 H ₂ gas in the plasma chamber 44.
It was introduced at 0 SCCM, and a phosphorus-doped microcrystalline silicon film was formed under the conditions of a pressure of 5.0 × 10 ⁻³ Torr and a microwave power of 1 kW. The film thickness is 1000Å. Next, this glass substrate was taken out from the ECR apparatus, and a conductive thin film was patterned into a size of 15 μm by a photolithography method.

After that, the substrate was set in the ECR apparatus again, and the buffer layer 5 was formed by the bias ECR method. First, evacuate the inside of the equipment to the level of 10 ^-7 Torr,
SiH ₄ is introduced into the film forming chamber 48 at a flow rate of 5 SCCM, O ₂ is introduced into the plasma chamber 44 at a flow rate of 5 SCCM, and Ar is 60 S.
Introduced at the flow rate of CCM, the pressure is 1.5 × 10 ^-3 Torr
The microwave generator 41 supplies 600 W of microwave power to the substrate and the high-frequency power source 53 supplies 1 to the substrate.
High-frequency power of 3.56 MHz and 800 W is applied, and Si serving as the buffer layer 5 on the photoconductive layer 3 and the conductive thin film 4.
An O ₂ film was formed to a thickness of 0.8 μm.

Dielectric thin films of TiO ₂ —SiO ₂ were alternately laminated on the buffer layer by electron beam evaporation to form a dielectric mirror 6 having a layer thickness of 3 μm. Further, a polyimide film having a film thickness of 2000 Å was formed thereon as the alignment film 7 by a spin coating method, and an alignment treatment was performed by rubbing. Next, in the same step as above, the other glass substrate 1 on which the transparent electrode 2 and the alignment film 7 were laminated was adhered via the spacer 8 so that the alignment films face each other, and the liquid crystal 9 was sealed between them. At this time, the liquid crystal used was a phenylcyclohexane nematic liquid crystal, and the cell gap was 6 μm.

Information was written in and read out by applying a voltage from the voltage applying means 10 to the photo-writing type liquid crystal light valve thus produced. A polarization beam splitter (not shown) is provided on the reading side.
The operating mode is the hybrid field effect mode. The obtained output pattern has excellent contrast, no reduction in resolution is observed, and nonuniformity of the pattern is also reduced. Insulation with a plurality of conductive thin films is provided between the photoconductive layer and the dielectric mirror. It was confirmed that the nonuniformity of the output pattern can be remarkably improved by providing the buffer layer made of the body material.

[0030]

According to the optically writable liquid crystal light valve of the present invention, a pixel-divided conductive thin film is provided between the photoconductive layer and the dielectric mirror, and an insulating material is formed on the conductive thin film. Since it has a buffer layer, it is possible to obtain a good resolution, it is possible to make the output pattern uniform, and it is possible to use it as a device that constitutes an image display and an optical information system. .

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a photoconductive type liquid crystal light valve of the present invention.

FIG. 2 is an electron cyclotron resonance plasma CV used for producing a photoconductive layer, a conductive thin film and a buffer layer of the present invention.
It is a schematic block diagram of a D device.

FIG. 3 is a cross-sectional view of a conventional photoconductive liquid crystal light valve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Transparent electrode 3 Photoconductive layer 4 Conductive thin film 5 Buffer layer 6 Dielectric mirror 7 Alignment film 8 Spacer 9 Liquid crystal 10 Voltage applying means 41 Microwave transmitter 42 Rectangular waveguide 43 Microwave introduction window 44 Plasma chamber 45 Inner bell jar 46 Plasma extraction window 47 Magnetic coil 48 Film forming chamber 49 Substrate 50 Substrate holder 51, 52 Gas introduction tube 53 High frequency power source

Claims (4)

[Claims] 1. A photoconductive liquid crystal light valve having a photoconductive layer, a dielectric mirror, and a liquid crystal layer between transparent electrodes provided on a pair of transparent substrates, the photoconductive layer and the dielectric mirror. A photoconductive liquid crystal light valve, characterized in that a plurality of conductive thin films and a buffer layer are provided between them. 2. The photoconductive liquid crystal light valve according to claim 1, wherein the conductive thin film is a crystalline thin film to which an element of group III or group V of the periodic table is added. 3. The photoconductive liquid crystal light valve according to claim 1, wherein the buffer layer is made of an insulating material formed by using a bias electron cyclotron resonance plasma CVD method. 4. The photoconductive liquid crystal light valve according to claim 1, wherein the photoconductive layer is made of an amorphous semiconductor formed by using an electron cyclotron resonance plasma CVD method.