JPH04130421A - Optical writing type liquid crystal light valve - Google Patents

Abstract

PURPOSE:To improve resolution by constituting a light reflection layer of a dielectric mirror formed by assembling two kinds of multilayered films having the functions of a light shielding layer and a reflection increase layer. CONSTITUTION:The light shielding layer 7 is formed on the photoconductive layer 4 by alternately and iteratively laminating 6 layers of Si-Ge layers and SiO2 layers. The reflection increase layer 8 is formed by iteratively laminating 6 layers of TiO2 and SiO2. The reflection increase layer 8 and the light shielding layer 7 constitute the light reflection layer. Since this liquid crystal light valve has the light reflection layer having high reflectivity and light shieldability in this way, the light valve has the high reflectivity and light shieldability, a high constant ratio and a high response speed and, therefore, the high-speed writing by a laser beam or the like is possible and the liquid crystal light valve having the high resolution is obtd.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical writing type liquid crystal light used in intermediate recording media of optical printers, image display devices, optical shutters, image processing devices, optical information processing systems, etc. It concerns valves.

[Summary of the invention]

The present invention relates to an optical writing type liquid crystal light valve that combines a highly sensitive photoconductive layer that exhibits high resistivity in the dark and high conductivity when illuminated with light, and a dielectric mirror that has appropriate conductivity and high reflectance. It is something.

The light reflection layer used in liquid crystal light valves is a dielectric mirror that combines two types of multilayer films that function as a light-shielding layer and a reflection-enhancing layer.The multilayer film that functions as a light-shielding layer is made of Si and Ge, which have high light absorption A layer made of the compound Si-Ge and 510
The 5t-Ge is a dielectric mirror in which two layers are alternately laminated, and the molecular formula of the 5t-Ge is 0.1 when its molecular formula is Si+-XGe++.
The composition was set to ≦x≦0.60. Further, the multilayer film having the function of an enhanced reflection layer is a dielectric multilayer film mirror using a dielectric material with low light absorption.

By using the optical writing type liquid crystal light valve having a light reflective layer according to the present invention, an optical writing type image projection device that can display high-definition images with little loss of readout light, has a fast writing speed, and can display moving images. [Conventional technology] Traditionally, in research on optical information processing and optical pattern recognition, it has been used to convert incoherent optical information into coherent optical information, Many optical writing type liquid crystal light valves have been studied in order to spatially modulate optical information.

In particular, Si/SiO2 multilayer film mirrors are used as dielectric mirrors that have high reflectance and electrical characteristics that match the parameters of the liquid crystal drive circuit in optical writing type liquid crystal light valves that read optical information using a reflective type. It's here.

In addition, Zr○z/SiO□ has a high reflectance.

S40. Research has been attempted to form dielectric mirrors using combinations of /Tilt, ZnS/MgFz, and the like.

[Problem to be solved by the invention]

However, when a dielectric mirror is fabricated using conventional Si/SiO7 as described above, the specific resistance in the in-plane direction of the mirror is too low, so when light is irradiated, a voltage is applied to the entire surface of the ferroelectric liquid crystal layer. There is a problem in that the resolution cannot be increased because the image may become blurred or uneven, or the image may not be written depending on the degree of the problem. Further, in a reflective type optical writing type liquid crystal light valve that reads out optical information, there is a problem in that the reflectance must be made higher and the light shielding property against the readout light must be increased. Further, a semiconductor junction between hydrogenated amorphous silicon (denoted by the symbol a-3t:H in the following description) which is a photoconductive film and a dielectric mirror also has the problem of exhibiting characteristics similar to those described above.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a structure in which the light reflective layer is a combination of multilayer films having two types of functions: a light shielding layer and a reflection enhancing layer, in order to increase the reflectance and light shielding properties of the light reflective layer. A dielectric mirror was used. The light-shielding layer is made of alternating layers of Si-Ge and Sin, which have a higher resistivity and greater light absorption than Si, and the reflective layer has a high reflectance using a dielectric material with small light absorption. A dielectric multilayer mirror was used. That is, by configuring the light reflective layer using a pair of 5j-Ge and Sin, the light reflective layer has a higher By increasing the specific resistance and improving the light shielding property against read light,
The above-mentioned problems have been solved by making it possible to construct an optical writing type liquid crystal light valve that has higher resolution and less influence of read light on the photoconductive layer.

In addition, by providing a reflective layer, a high reflectance for read light can be achieved, and an optical writing type liquid crystal light valve with low read light loss can be achieved, thus solving the above problems.

Furthermore, in order to eliminate the semiconductor junction between the photoconductive film a-3i:H and the dielectric mirror, an insulating film Sin is formed on the a-3i:H, and a dielectric mirror is formed on it. By doing so, the semiconductor junction between a-8i:H and Si-Ge was avoided, and the above problems were solved.

[Example] Figure 1 shows an example of the present invention, which combines a highly sensitive photoconductive layer that exhibits high resistivity in the dark and high conductivity when irradiated with light, and a dielectric mirror that has moderate conductivity and high reflectance. FIG. 2 is a cross-sectional view showing the structure of an optical writing type liquid crystal light valve.

In this example, first, transparent glass substrates were prepared as the transparent substrates 1a and lb, and anti-reflection coatings 6a and 6b were formed on the outer surfaces of the transparent substrates 1a and 1b. Transparent electrode layer 2a
, 'lb, an ITO transparent electrode layer was formed on the inner surfaces of the transparent substrates 1a and 1b.

Further, on the optical writing side transparent electrode layer 2a, a 2 to 3 μm thick intrinium a-3i:H was formed by discharging and decomposing a gas containing SiF as a living body to form a photoconductive layer 4.

Furthermore, a light shielding layer 7 was formed on the photoconductive layer by repeatedly stacking six Si--Ge layers and SiO2 layers alternately. On top of that, six layers of TlO2 and 3402 were repeatedly laminated to form the reflective layer 8. These reflection enhancing layer 8 and light shielding layer N7 constitute the light reflecting layer of the liquid crystal light valve of the present invention. Further, on the reflection-enhancing layer 8 and the transparent electrode 2b on the projection side, a film thickness meter was installed, in which -silicon oxide (SiO) was set at an angle of 82 degrees with respect to the normal direction of the substrate and in the normal direction of vapor deposition. The liquid crystal alignment layers 3a and 3b were formed by oblique vapor deposition to a thickness of 200 nm. The transparent substrates 1a and lb are arranged with their alignment film layers 3a and 3b facing each other, and a gap is controlled and formed using an adhesive containing glass fibers having a diameter of 1.5 μm via a spacer 9 to form a ferroelectric liquid crystal layer 5. I tried to hold it between them. The encapsulated ferroelectric liquid crystal composition is an ester-based SmC liquid crystal mixture containing 4 (
(4″-octyl)phenyl)benzoic acid (3′-fluoro, 4″-octyloxy)phenyl ester, and 4-
14°-octyloxy)benzoic acid (3゛fluoro0.
A 1:1 mixture of 4" octyloxy) phenyl ester was used, and 25% by weight of 5-octyloquinaphthalenecarboxylic acid and 1"-cyanoethyl ester were added as optically active substances to form a ferroelectric liquid crystal. Of course, it goes without saying that liquid crystal compositions other than the above-mentioned strong v?Jt liquid crystal composition may be used in the liquid crystal light valve of the present invention.

FIG. 2 is an enlarged view of the vicinity of the reflection-enhancing layer 8 and the light-shielding layer 7 in FIG. 1, and is a sectional view showing the structure of the light-reflecting layer according to the present invention. Si-Ge layer 15 on photoconductive layer 4
(n is a natural number), and the Si-
A light shielding layer 7 in which a Si--Ge layer 15 having the same composition as the Ge layer is formed to a thickness of about 58 nm, and a SiOt jiF layer is formed on the light shielding layer N7.
14b to about 94 nm and T r Oz layer 13 to about 60 nm.
It has a structure in which the reflection-enhancing M8 is repeated m times (m is a natural number). These light shielding layer 7 and reflective layer 8
The film thickness of each layer constituting the film is 1/4 film (thickness = λ/4 n: n is the refractive index of each layer) for a predetermined wavelength λ of light.
It is preferable to set it so that

As the photoconductive layer 4, a-3i:) (prepared in the same manner as described in the example of FIG. 1 was used.
The light-shielding layer 7 and the reflection-enhancing layer 8 were produced using a vacuum evaporation method using electron beam heating. Moreover, the Si-Ge layer 15 is
The thin film had a composition of S i 0.59G e O,41. However, the composition of the Si--Ge layer 15 is a value obtained by analyzing the composition of the core layer using Auger spectroscopy. It goes without saying that as a method for producing the light-shielding layer 7 or the reflective layer 8, a sputtering method, a chemical vapor deposition method, or the like may be used in addition to the vacuum evaporation method.

Further, SiQt was sandwiched as an insulating layer 12 between a-3i:H as the photoconductive layer 4 and the light shielding layer 7. As a result, the Si-Ge layer 15 used for the photoconductive layer 4 and the light-shielding layer 7
Avoided semiconductor junctions with

This made it possible to prevent phenomena such as voltage being applied to the entire surface when irradiated with light or blurring of the recorded image, which would deteriorate resolution due to the in-plane specific resistance being too low. Although Sing was used for the insulating layer 12 this time, it is also possible to use other insulating layers such as Ge○z, TrOx, AI, O□, and the like.

FIG. 3 shows the Si-Ge layer used in the present invention.
This figure shows the characteristics of specific resistance with respect to the composition ratio of the -Ge thin film. Note that the Si-Gem film was produced by the vacuum printing method using electron beam heating as described above. The specific resistance of the ferroelectric liquid crystal of the liquid crystal light valve of the present invention is 10 to 1012Ωχ. The specific resistance of T:a-3i:H is lOSΩX cm in bright and dark conditions, and 10” to 10 in dark conditions.
To drive a liquid crystal light valve, the specific resistance of the dielectric mirror is preferably 109 to 1010 Ωχ.The horizontal axis represents the composition ratio X of St+-xGe, l, and the vertical axis represents its specific resistance. The specific resistance ρ at the time of composition was taken. From Figure 3, it was found that the specific resistance of the dielectric mirror becomes 109 to 10I0Ωχ when the composition ratio X is 0.25 to 0.50. In the characteristics shown by the solid line in Figure 3, the value of Since it was found that the AvA and Bl in the composition vary within the range, it is considered preferable to set the composition ratio to 0.1≦x≦0.60.

FIG. 4 is a graph showing a comparison between the spectral characteristics of the light-reflecting layer of the liquid crystal light valve of the present invention and a conventional light-reflecting layer. In FIG. 4, 16 is the spectral reflectance of the light-reflecting layer according to the present invention, 17 is the spectral transmittance of the light-reflecting layer according to the present invention, 18 is the spectral reflectance of the conventional light-reflecting layer, and 19 is the spectral reflectance of the conventional light-reflecting layer. This is a curve showing the spectral transmittance of . As a conventional light reflection layer, a pair of Si layer and SiO□ layer, each having a film thickness of about 58 nm and about 89 nm, was repeated seven times on a glass substrate, and then an St layer with a film thickness of about 58 nm was formed. I used something. Further, as a light reflecting layer related to the present invention, a Si-Ge layer with a thickness of about 58 nm and a Sin! layer on a glass substrate is used. Approximately 8 layers
9nm was repeated three times, and the Si-Ge
A light-shielding layer is formed by forming a Si-Ge layer with a thickness of about 58 nm having the same composition as that of the Si-Ge layer, and a Si-Ge layer of about 94 nm and TiO□ on the light-shielding layer.
A structure was used in which a reflection increasing film 8 was combined with a layer having a thickness of about 60 nm and repeated three times. At the predetermined wavelength shown in FIG. 4, the spectral reflectance of the light reflecting layer according to the present invention is 9.
The spectral transmittance is 9.95% or more, and the spectral transmittance is 0.05% or less, and the spectral reflectance at the same wavelength of the conventional light reflective layer is 8.
6% and spectral transmittance of 0.18%, it was found that it has extremely excellent characteristics. By using the light-reflecting layer of the present invention in this way, it is possible to form a light-reflecting layer with high spectral reflectance and low spectral transmittance for a predetermined wavelength of light. Even if an image is written while irradiating a readout light stronger than that of a liquid crystal light valve using a liquid crystal light valve, the image is written without the readout light affecting the photoconductive layer constituting the liquid crystal light valve. was completed.

In addition, when writing and reading images of a resolution chart using an optical writing type liquid crystal light valve using a light reflecting layer according to the present invention, the limit resolution was approximately 1501p.
An extremely high resolution of /mm was obtained. Although it is known that forming a light reflective layer in a conventional optically writable liquid crystal light valve causes the resolution to become extremely poor, the optically writable liquid crystal light valve using the light reflective layer according to the present invention has been developed. uses ferroelectric liquid crystal and has almost the same resolution as a conventional optical writing type liquid crystal light valve that does not have a light reflective layer. This is because the light-reflecting layer according to the present invention can achieve high spectral characteristics with a smaller number of layers than conventional light-reflecting layers, so that less charge dissipates within the plane of the light-reflecting layer. It can be inferred that this is because the specific resistance of the light reflecting layer has an appropriate value as described above, so that impedance matching is excellent.

When writing image information, etc. to the optical writing type liquid crystal light valve according to the present invention using an LD, LED, etc., first of all, the entire surface of the liquid crystal light valve is irradiated with light, and a DC voltage sufficiently higher than the operating threshold voltage is applied. When applying a voltage or without light irradiation, apply a DC bias voltage that is sufficiently larger than the operating threshold voltage in the dark to align the ferroelectric liquid crystal to a stable state in one direction. Perform the memorization process.

Next, without light irradiation, the operating threshold is 4rL in the dark.
Apply a DC voltage of opposite polarity that is below the voltage and above the operating threshold voltage during light irradiation, and
Image information to be projected and displayed is written with light using an optical writing means such as an ED.The photoconductive layer used here is 700.
Since it has a sufficiently high sensitivity to light with a wavelength of ~850 nm, for example, when irradiated with a semiconductor laser having a center wavelength of 780 nm, the photoconductive film 15 irradiated with light generates carriers and enters a low resistance state. The applied bias voltage is applied to the liquid crystal layer in a resistance-divided form and excites the liquid crystal molecules. The region that is not irradiated with light maintains a high resistance, and therefore, almost no voltage is applied to the liquid crystal molecules, so the liquid crystal molecules are not excited, and as a result, the alignment direction of the liquid crystal molecules in the light irradiated area and the non-light irradiated area is changed. It will be stored in memory with different values.

The image information written in this way is reflected by the reflective layer when linearly polarized projection light that has passed through the polarizer is projected onto the screen after passing through the analyzer. When the contrast ratio between the bistable states was measured using a polarizing plate with a degree of polarization of 99.9% and a single transmittance of 38% as a polarizer and an analyzer, it showed an extremely high value of 400:1 or more. In liquid crystal display modes such as TN type and DSM type that do not have bistability or memory properties, the amount of reflected light is modulated by the voltage directly applied to the liquid crystal molecules, but the image retention time is difficult to determine. It's short.

It goes without saying that the operation method of the optical writing type liquid crystal light valve described above may use a gas laser such as a helium neon laser or an argon laser, or a solid laser such as a YAG laser for writing and/or reading out an image. stomach.

On the other hand, according to the present invention, the light reflectance cannot take halftones and becomes 1 or 0 due to its operating threshold characteristic and bistable memory property, but the written image is determined by the operating threshold from the outside. It will be held semi-permanently unless a voltage higher than the voltage is applied or strong pressure is applied. After the image was formed, the voltage was set to oven condition and the measurement was repeated three days later, and it was confirmed that the contrast ratio hardly changed, and that it had extremely excellent memory properties.

Next, a case where the liquid crystal light valve of the present invention is applied to an incoherent-coherent converter will be described. In this case, the photoconductive layer 4 shown in FIG. 1 is made of vacuum-deposited CdS, Se, 5eTe, etc., an organic material, or a functionally separated multilayer structure. The rest of the configuration is the same as above, so
The explanation will be omitted.

According to the above-described incoherent/coherent converter, an image is formed on the ferroelectric liquid crystal layer by incoherent writing light from the outer surface of the cell, and the image formed by the writing is different from the applied voltage during warm-up writing. The alignment direction of liquid crystal molecules aligned by applying an electric field opposite to the direction (
By irradiating coherent projection light through a polarizer with its polarization axis set perpendicular to the polarization direction), and by projecting it through an analyzer perpendicular to (or parallel to) the polarization direction of the reflected light during total erasure. Can be read.

In addition, in FIG. 1, when the liquid crystal light valve of the present invention is to be operated at high speed, the voltage polarity on the transparent electrode layer 2a side is changed to positive, negative, or zero voltage while constantly irradiating the writing light and reading light. Pulse voltage that is repeated in sequence,
It is preferable to use a driving method in which the voltage is applied continuously between the transparent electrode layers 2a and 2b, erasing is performed when a positive voltage is applied, writing and reading is performed when a negative voltage is applied, and reading is performed when a voltage is zero. During this writing, electron and hole pairs are generated in the a-3t:H photoconductive layer 4 on both the writing side and the reading side. In the case of a-3i:H photoconductive layer,
The mobility of electrons is several to several tens of times greater than the mobility of holes, and photoconduction phenomena are dominated by electrons. Therefore, a transparent electrode layer 2 is added to the transparent electrode layer of this liquid crystal light valve.
If a pulse voltage is applied such that the voltage polarity on the a side is repeated in the order of positive, negative, and zero voltage, the polarity on the transparent electrode 2a side of the pulse voltage applied to both ends of the liquid crystal light valve becomes positive. In this case, the electrons generated by the read light become carriers and move toward the transparent electrode 2b, completely inverting the ferroelectric liquid crystal molecules.If the polarity is negative, the electrons generated by the read light become carriers and move toward the transparent electrode 2b, and if the polarity is negative, The generated electrons move toward the liquid crystal side, and as a result, only the ferroelectric liquid crystal molecules in that region are inverted to a stable state corresponding to the opposite polarity, and a desired image can be recorded. However, aSi :H
If the intensity of the readout light reaching the photoconductive layer 4 is too strong,
Even when the polarity of the pulse voltage on the transparent electrode 2a side is negative, excessive holes are generated deep in the photoconductive layer over the entire region irradiated with the readout light. As a result, in the photoconductive layer, electrons move toward the liquid crystal side not only in the area irradiated with the write light but also in the area irradiated with the read light, and the entire surface of the liquid crystal light valve becomes in the write state. . Therefore, the readout light intensity reaching the photoconductive layer is required to be smaller than a predetermined value.For example, when using a liquid crystal light valve having the configuration shown in FIG. Intensity 160μW/
It has been found that if writing light of cm2 is used, it is desirable that the reading light intensity is 60 to 70 .mu.W/cm2 or less. However, when applying an optical writing type liquid crystal light valve to a spatial light modulator such as an incoherent/coherent converter used in optical information processing or an image projection display device, the readout light is approximately 1 to 100 mW/cm2. In many cases, strong light is used. When using a conventional optical writing type liquid crystal light valve with a light reflective layer as shown in Figure 4 18 and 19, only a readout light of about 1 to 40 mW/cm2 can be used, which completely satisfies the above specifications. I can't do it. However, in the optical writing type liquid crystal light valve using the light reflective layer according to the present invention, FIGS.
As can be seen, any readout light of 140 mW/cm2 or less can be used, and the above specifications are satisfied.

The same problem as above occurs when a TN type liquid crystal, DSM type liquid crystal, etc., which does not have bistability or memory properties, is applied to the optical writing type liquid crystal light valve of the present invention. In this case, since the optical writing type liquid crystal light valve does not have memory characteristics, it must be used by simultaneously irradiating write light and read light. However, for the same reasons as mentioned above, this problem can be avoided by using the light reflective layer according to the present invention.

[Effects of the Invention] As explained above, according to the optical writing type liquid crystal light valve having a light reflection layer with high reflectance and light-shielding property of the present invention, in addition to having high reflectance and light-shielding property and a large contrast ratio, Because the response speed is fast, high-speed writing using laser light is possible, making it possible to create high-resolution liquid crystal light valves. Therefore, spatial light modulators such as high-resolution, large-area, high-speed incoherent-coherent converters, and high-contrast ratios enable high-speed addressing with light such as lasers, allowing for erasing and rewriting. In addition, high-density optical bistable memory that does not require a backup source can be realized, which can be used as an intermediate recording medium for optical printers.
This will dramatically increase the performance and range of applications of image display devices, optical shutters, coherent optical correlation systems, other image processing devices, optical information processing and measurement systems, etc.

[Brief explanation of drawings]

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 cross-sectional view showing the structure of a light-reflecting layer according to the present invention, and FIG. 3 is a cross-sectional view showing the structure of a light-reflecting layer according to the present invention. FIG. 4 is a graph showing the relationship between the specific resistance ρ and the composition ratio X of the Si--Ge layer, Si+-xaex. FIG. 4 is a graph showing the spectral characteristics of the light-reflecting layer according to the present invention. Ia, Ib...Transparent substrates 2a, 2b...Transparent electrode layers 3a, 3b...Alignment film layer 4...Photoconductive layer 5...Ferroelectric liquid crystal layer 6a, 6b...Non-reflection Coating layer 7...Light blocking layer 8...Reflection enhancing layer 9...Spacer 10...Writing light 11...Reading light 12...Insulating layer 13...Ti02 layer 14...SiO□ Layer 15a, 15b-Si-Ge layer 16...Spectral reflectance of the light reflecting layer related to the present invention 17...Spectral transmittance of the light reflecting layer related to the present invention 18...Spectral spectrum of the conventional light reflecting layer Reflectance 19...More than spectral transmittance of conventional light reflecting layer

Claims (4)

[Claims] (1) In an optical writing type liquid crystal light valve in which a writing means using light such as a laser beam or an LED, a photoconductive layer, a light reflection layer, a liquid crystal alignment layer, a liquid crystal layer, and a voltage application means are formed, the light reflection layer has the functions of a light-shielding layer and a reflective layer 2
2. The writing type liquid crystal light valve according to claim 1, wherein the write type liquid crystal light valve is a dielectric mirror combining different types of multilayer films. (2) The multilayer film that functions as a light-shielding layer of the light-reflecting layer is made of Si.
A dielectric mirror in which layers of Si-Ge and SiO_2 layers are alternately laminated, and the Si-Ge has a molecular formula of Si_1_-_xGe_x of 0.
The optical writing type liquid crystal light valve according to claim 1, having a composition of 1≦x≦0.60. (3) The optically writable liquid crystal light valve according to claim 1 or 2, wherein the multilayer film having the function of a reflection enhancing layer is a dielectric multilayer film mirror using a dielectric material with low light absorption. (4) The optical writing type liquid crystal light valve according to any one of claims 1, 2 and 3, further comprising an insulating layer between the photoconductive layer and the light shielding layer.