JPH03273216A - Space light modulator and production thereof - Google Patents

Abstract

PURPOSE:To obtain the optical switching characteristic suitable for an optical arithmetic unit and to enable the stable operation by forming a photoconductive layer of a spacific high polymer. CONSTITUTION:The photoconductive layer is formed of the high polymer expressed by formula I. In the formula I, n>=2, i=1, 2,..., n; X1 is any of O, S, SE, and Te; Y1 is an arom.or substd. arom. group. The high polymer expressed by the formula I has a high photosensitivity and can be changed in the film quality by the same high polymer in order to function the polymer as a unidirectionally oriented film. The dielectric constant of this high polymer has the value approximate to the value of a liquid crystal layer when this high polymer is used as the oriented film of an optical modulating element. The formation of the area of liquid crystal picture elements to the same area for photodetection in device design is then possible. The photoconductive layer is formed on the substrate surface without forming patterns in this way and the stable optical switching characteristic is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a spatial light modulation element used in an optical arithmetic device or a projection display. Although a photo-writing type device in which a photoconductive layer such as amorphous silicon or CdS and a nematic liquid crystal are laminated has been proposed, the problem to be solved by the invention is spatial light modulation by the combination of a photoconductive layer and a liquid crystal layer. The device controls the alignment state of the liquid crystal by being irradiated with light through the photoconductive layer.If an inorganic photosensitive material such as amorphous silicon or CdS is used for this photoconductive layer, the ratio of the light-receiving area of the photoconductive layer to the area of the liquid crystal pixel and The film thickness is designed to fulfill the switching function.If the dielectric constant of the liquid crystal is εLe, and the dielectric constant of the photoconductive layer is εPH, it is designed to satisfy the following relational expression: εLCS LC/d tc < εpssPH/d
ps Therefore, for example, if we consider εptt~11 of amorphous silicon as the photoconductive layer, then S+ as εLC~3
, c:SPH~1:0.1(dLc~5μdPH~1μ
Therefore, the disadvantage is that the incident light cannot be used effectively.Also, there is an alignment film, which is an insulating layer, between the photoconductive layer and the liquid crystal layer, and charge accumulation at the interface becomes a major problem. Means for Solving the Problem In a liquid crystal cell in which a liquid crystal layer and a photoconductive layer are sandwiched between opposing conductive electrodes, the photoconductive layer is made of a polymer represented by the general formula (A) and the liquid crystal layer is aligned between the layers. At least one of the membranes has the general formula (
A first layer of the general formula (b) is formed on a substrate on which conductive electrodes are formed, sandwiching a liquid crystal, and a polymer layer represented by (b) is heated, followed by a second layer of the general formula ( B)
A spatial light modulator is manufactured by forming a polymer and heat-treating it at a temperature lower than the heating temperature of the first layer.The polymer represented by the general formula (a) has high photosensitivity. In the case of a polyimide film expressed by the formula (b), it also functions as an alignment film for the liquid crystal layer.
We discovered that the polymers described in a) and (b) lead to a significant increase in sensitivity due to increased crystallinity.On the other hand, it is also possible to make the same polymer function as an alignment film by changing its film quality. In the case of a polyimide film expressed by formula (b), the difference between the crystallization temperature and imidization temperature is used. The film as a photoconductive layer is formed by coating a precursor polyamic acid on a conductive substrate, imidizing it, and then crystallizing it at a high temperature at the melting point of the polymer.The second layer as an alignment film is formed on the photoconductive layer. Coating the same polyamic acid and forming it by imidization
The alignment treatment is performed by a rubbing method. In this method, the polymer is formed using a coating method from a solvent.It is also possible to use a vacuum evaporation method.If this polymer is used as an alignment film for a light modulation element, firstly, the dielectric constant is εPM~ which is close to that of the liquid crystal layer. 4. In designing the holding plate device, it is possible to make the liquid crystal pixel area and the light-receiving area the same. This also means that the photoconductive layer can be formed without patterning on the substrate surface, and the polymer (b) that functions as an alignment film is a carrier. It has excellent transmission ability, little charge accumulation within the film, and exhibits stable optical switching characteristics.

Embodiment An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a sectional view of an embodiment of the spatial light modulation element of the present invention. Element structure tl;L A transparent conductive electrode 102 (e.g. ITO) is placed on a transparent insulating substrate lO1 (e.g. glass).
A liquid crystal 104 is sandwiched between a laminated photoconductive layer 103 of polymer (A) and a substrate having an ordinary alignment film 105.Photoconductive layer 1
For example, nematic liquid crystal, ferroelectric liquid crystal, and liquid crystal polymer are used as materials for the liquid crystal layer, while various polyimide films are used as the alignment film. The transparent insulating substrate 101
A glass substrate is used as a transparent conductive electrode 10 on this.
2, IT○ with a thickness of 0.1 to 0.5 μm is formed by a sputtering method to form a photoconductive layer 103. The material of the photoconductive layer 103 is benzophenonetetracarboxylic dianhydride (hereinafter referred to as BPDA). and oligoparaphenylene sulfide diamine (oligomer with polymerization degree n, referred to as 5DA-n). i&BPDA and 5DA
-n in the solvent dimethylacetamide (referred to as DMAc). This polyamic acid was applied to the surface of the substrate using a spinner to a thickness of 1 to 10 μm. After coating, the substrate was placed in a heat treatment furnace for t1. ．． Heat treatment is performed at 300°C for 2 hours.

In this process, the polyimide film is imidized and crystallized, and the other substrate 107 is coated with polyvinyl alcohol and dried to obtain a film of ~100 OA.A raw linking process is applied to both substrates. These substrates were pasted together with a cell gap of 5 to 7 μm, and a liquid crystal material LI○ Although alternating current and direct current are superimposed with an applied voltage in between, Figure 2 shows the liquid crystal alignment state when only the direct current component Voc is applied as the applied voltage and 10 times the amount of light is irradiated from 1601 ux in the dark to 16001 ux in the bright. is expressed as capacitance C
When irradiated with light, the electrical resistance of the photosensitive layer 103 decreases, and the liquid crystal layer 1
As the electric field applied to VDC becomes stronger, the liquid crystal molecules align perpendicularly to the substrate. Even if you superimpose
Fig. 4 shows the spectral sensitivity characteristics when the irradiation light is monochromatic light. BPDA-Ph3, a photoconductive material, has charge current characteristics that correspond to light absorption characteristics, but in the visible light wavelength region, it has a charge current characteristic of 600 nm.
Figure 5 shows the dependence on light irradiation energy when irradiating with a wavelength of 400 nm.The alignment state responds nonlinearly as the irradiation light intensity increases under the condition that the applied voltage is constant. Example 2 Example 1 Open bale BPDA- as photoconductive polyimide film
A spatial light modulator was fabricated using Ph3.9 The device configuration was the same as that shown in Figure 1.A two-layer structure was used in which an alignment film was laminated on the photoconductive layer 103. .

Transparent electrode IT○102 using a spinner with polyamic acid
The polyimide film is then crystallized. Apply 100 OA of the same polyamic acid on top of the crystallized plum film, dry and heat for 4 hours in the air at 300°C.
℃ for 1 hour to obtain an imidized film. Although this second layer is an amorphous film, the second imidized film 105 mentioned above is directly formed on the electrode 106 on the opposing substrate. This substrate is rubbed. The optical response characteristics of the spatial light modulator manufactured in the same manner as in Example 1 were evaluated, except that a liquid crystal was sealed between both substrates.The results are shown in FIG.

Example 3 Photoconductive polyimide M (Other crystallization method) The photosensitivity and liquid crystal orientation change greatly depending on the orientation.To control this film, the synthesis conditions of polyamic acid, which is the precursor of the polyimide film, and the synthesis of polyamino acid to polyimide were used. It is possible depending on the conditions of thermal imidization or crystallization of 4BPDA-
Using Ph3, raw material B is used as a polyamic acid synthetic leather condition.
f knee by changing the synthetic leather molar ratio of PDA and 5DA-3.
In addition, the heating temperature is 30°C to control imidization and crystallization.
For the synthesis of polyamic acid, the molar ratio of BPDA and 5DA-3 is usually 1:1.
+5DA-3) and define the molar ratio, 4X>0.5
Under these conditions, the carboxylic acid is in excess for polymer synthesis. FIG. 7 shows the X-ray diffraction pattern showing the change in the crystallization state after heating when X is changed around 0 and 5. Heating conditions are constant at 300℃ for 2 hours, LX≦0.5
In this case, it is an amorphous film, but when X>0.5, it becomes a crystalline film.Furthermore, in the range of X>0.5, as the ratio increases, the interplanar spacing d=4. X for d=4.8A of OA
Figure 8 shows how the line scattering intensity ratio increases.The plane spacing d=4.8A corresponds to the plane spacing between adjacent molecules of polyimide molecules, so the condition is such that X is close to 0.5. The crystalline film exhibits an orientation in which molecules are aligned parallel to the substrate, whereas an increase in FIG. 9 shows changes in photosensitivity characteristics depending on heating temperature. As X increases, the heating temperature range in which a significant increase in photosensitivity can be obtained expands.In the case of 4X=0.51, it is 300±20℃, whereas in the case of X=O, S6, it is as wide as 300±50℃. The correlation between the orientation of the polyimide film and the orientation when the liquid crystal layer is sandwiched between the polyimide films was evaluated.
A polyimide coating film (thickness 1000A) under different conditions is rubbed and a guest-host type is encapsulated as a liquid crystal material.The absorption of incident light polarized in the orientation direction of this panel and light polarized in the perpendicular direction is The degree of orientation is defined by the dichroic ratio obtained from: Degree of orientation of polyimide film Y=I4゜8/ CI 4.8 + I 4.0)
(I4.8 is the scattering intensity of d=4.8A, I4.0 is d
=4. It represents the scattering intensity of OA. ) and the dichroic ratio, R, are shown in Figure 1O. In the region where a crystal film is obtained, a film with a large scattering intensity ratio of 4.8 has a good liquid crystal orientation of 1. % From the photosensitivity characteristics and orientation characteristics, the optimum condition for the polyimide film of the spatial light modulator is a crystal film that gives the maximum value of the degree of orientation Y, and the result obtained by optimizing the heating conditions near L Based on these film forming conditions, a single layer polyimide film of 5 μm thick was obtained on the glass/IT○ electrode.
A The other polyimide film was set to 100 OA under the same conditions, and the liquid crystal was sealed in both substrates, and the applied voltage was set to AC VAC = 4 V? , :, Figure 11 shows the optical switching characteristics caused by 400 nm light irradiation.

Example 4 Materials for a photoconductive polyimide film were investigated. Three types of carboxylic acids: BPDA, PMDA (pyromellitic dianhydride), and BIDA (biphenyltetracarboxylic dianhydride). 5DA-3 as a diamine. There are three types: , 5, and 7. Each polyimide film is used in a structure that doubles as an alignment film and a photoconductive film. Figure 12 shows the results.

Example 5 An optical neural network was constructed using the spatial light modulator of Example 1, and its functional operation was confirmed.The configuration is shown in Figure 13.The back propagation learning method (pack propagation method) was used. , microlens arrays 122, 12
4. Input image 1 from the learning mask pattern 123 and the light threshold element 125 by the spatial light modulation element of this embodiment
21 displays 26 letters of the alphabet in a 7 x 8 matrix.Learning mask pattern 123 consists of a 49 x 64 matrix, and the transmittance is changed so that the 8-gradation display obtained by the BP method can be expressed by the transmitted light intensity. The optical threshold element 125 is a 7 x 8 matrix, and each pixel is focused with transmitted light from a 7 x 8 mask pattern by the microlens array 124. When the 26 letters of the alphabet were associated using this system, the recognition rate was 100%.Example 6 A reflective spatial light modulator shown in FIG.
A photoconductive layer 203 of BPDA-
Ph3 is formed to a thickness of 5 μm, and a metal thin film of A1 is formed as the light reflection layer 205. Furthermore, since a white light source is used as the writing light 212, the light that is transmitted without being absorbed by the photoconductive layer 203 may be absorbed by the light absorption layer 204. A liquid crystal layer 207 is sandwiched between alignment films 206 and 208. A projection display was constructed using this reflective spatial light modulator and a high-contrast image was obtained.Example 7 Ferroelectric liquid crystal was used to realize high-speed switching operation. Although the panel configuration in which the spatial light modulation element used was created is shown in Figure 1, the liquid crystal 104 is a ferroelectric liquid crystal FELIX-001 (
(manufactured by Hoechst) with a cell gap of 2 μ and t4
White light was irradiated with an applied voltage of 20 V and a driving frequency of 1 kHz, and changes in the light intensity of the transmitted light were evaluated.The results are shown in FIG. 15 in terms of frequency response. The panel characteristics of the ax are 20
Even though a response of 0 μsec is possible, the spatial light modulator of the present invention has optical switching characteristics suitable for optical processing devices.Although it exhibits stable operation, it is easy to manufacture with a structure that also serves as an alignment film and a photoconductive layer. The film quality is also low in electrical resistance, so the effect of space charge accumulation is small (it provides high contrast images when used as a single projection display).

[Brief explanation of drawings]

Figure 1 is a cross section of one embodiment of a spatial light modulator using the photoconductive polymer of the present invention & Figures 2 and 3 are cross sections of the spatial light modulator shown in Figure 1 in Example 1. Figures 4 and 5 show the same spectral sensitivity characteristics in Example 1. Figure 6 shows the response characteristics of the two-layer alignment film in Example 2. Figures 7 and 8 show the response characteristics of the spatial light modulator with the structure to incident light energy. Fig. 10 shows the orientation characteristics of the polyimide film with respect to the heat treatment temperature. Figure 12 shows the spectral sensitivity characteristics of optical switching of spatial light modulators with different polyimide films in Example 4. & Figure 13 shows the structure of the optical neural network in Example 5. &&
Figure 14 is a cross-sectional view of the configuration of the reflective spatial light modulator in Example 6. Figure 15 is a diagram showing the frequency dependence of optical switching of the spatial light modulator using ferroelectric liquid crystal in Example 7. 101, 107...Transparent substrate 102, 106...
...Transparent conductive K 103...Photoconductive N, 104
...Liquid crystal 105...Alignment film 108...
...Spatial light modulation element, 109...Polarizer,
110...Analyzer, 111...Incidence i
112... Emitted light 201, 210... Transparent substrate 202, 209... Transparent electrode 203
...Photoconductive layer 204...Light absorption layer 205.
...Light reflecting screen 206, 208...Alignment film 207
...Liquid crystal 211...Reading light 212...
...Signal light 213...Polarizer, 214...
Analyzer.

Claims (7)

[Claims] (1) A spatial light modulation element in which a liquid crystal layer and a photoconductive layer are sandwiched between opposing conductive electrodes, wherein the photoconductive layer is made of a polymer represented by general formula (A). ▲There are mathematical formulas, chemical formulas, tables, etc.▼(a) n≧2, i=1, 2,..., n X_i: Any of O, S, Se, Te Y_i: Aromatic or substituted aromatic group (2) The spatial light modulator according to claim 1, wherein the polymer is polyimide represented by the general formula (b). ▲There are mathematical formulas, chemical formulas, tables, etc.▼(b) Z: Group containing aromatic group (3) The spatial light modulator according to claim 1, wherein the liquid crystal layer is a ferroelectric liquid crystal. (4) Between the photoconductive layer and the liquid crystal layer, there is a light absorption layer that has a larger absorption coefficient than the photoconductive layer for light of a certain wavelength and a light reflection layer that has a higher reflectance for light that passes through the liquid crystal layer. The spatial light modulator according to claim 1 or 2, characterized in that: (5) The spatial light modulator according to claim 1, wherein at least one of the alignment films sandwiching the liquid crystal layer is a polymer layer represented by the general formula (b). (6) A claim characterized in that at least one of the polymer layers sandwiching the liquid crystal layer is composed of two or more layers, the top layer is an amorphous polymer, and the polymer layer closer to the substrate than that layer is a crystalline polymer. Item 5. Spatial light modulation element according to item 5. (7) A first layer of the general formula (b) is formed on a substrate on which conductive electrodes sandwiching a liquid crystal are formed, and a heat treatment is performed. Subsequently, a second layer of a polymer represented by general formula 2 is formed and heat-treated at a temperature lower than the heating temperature of the first layer.