JPH09329783A - Spatial light modulation element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evade the reduction of a contrast ratio and resolution and fanlis due to the defective alignment of liquid crystal molecules and to obtain satisfactory display quality by locally arranging spacer for controlling the thickness of liquid crystal(LC) around a display part without distributing them on the display part and sufficiently thickening a transparent substrate. SOLUTION: After lapping the surface of an LC alignment layer, thermosetting epoxy group adhesive 7 into which spacer 6c is mixed is applied to the surfaces of a transparent electrode layer 2a and an LC alignment layer 6b so as to surround a display part while remaining only an LC injection port. IN this case, the spacer 6c for holding the thickness of an LC layer at a fixed value is arranged so as not to be included in the display part and the thickness (h) of a 2nd transparent substrate 2 to be a rectangular plate having the thickness (h) and the length a×b of the side is a value satisfying h<3> >= 12p(1-ν<2> )}/ π<4> wE(1/a<2> +1/b<2> )<2> }. In the inequality, (w) is the variation of a center part at the time of applying external load (p) to the substrate 2, ν is the Poisson's ratio and E is Young's modulus.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention makes writing light containing information incident on a photoconductor layer and applying an electric field corresponding to the intensity distribution of the writing light to the liquid crystal layer, whereby the reading light incident on the liquid crystal layer is applied. An optical writing type spatial light modulator (Spatial Light Modulator: hereinafter SL) that modulates and emits
(Abbreviated as M).

[0002]

2. Description of the Related Art An optical writing type SLM can be applied to mutual conversion between incoherent light and coherent light, parallel processing of data, direct arithmetic processing of an image, and display of a video projector using a light intensity amplifying function. It is.

An optical writing type SLM generally has four layers of a photosensitive layer, a light shielding layer, a mirror layer and an electro-optical effect layer between two transparent substrates on which transparent electrode layers are formed. The photoconductor layer has a high resistivity when no light is incident, and has a property of significantly decreasing when light is incident.
It is composed of a material such as dS or amorphous silicon hydride (a-Si: H). The mirror layer serves to spatially separate the writing light and the reading light, and the degree of optical isolation determines the signal amplification factor of the SLM. As the mirror layer, for example, a dielectric multilayer film in which SiO ₂ films and TiO ₂ films are alternately laminated is used. Shielding layer is provided between the photosensitive layer and the mirror layer, and a role to enhance the isolation of the writing light and reading light, for example, SiO ₂
A Cu cermet film is used. The electro-optical effect layer has a property of changing optical characteristics such as refractive index, scattering, and optical rotatory power according to an applied electric field, and an electro-optical crystal or liquid crystal is used.

An adhesive is usually used to hold these four layers between two transparent substrates. Adhesive is SL
In order to impart a uniform function to the entire surface of the display portion of M, it has a role of keeping each layer stable and a role of blocking each layer from the outside to prevent the performance deterioration thereof. Especially,
When a liquid crystal layer which is a fluid is used as the electro-optical effect layer, a spacer is often used in order to keep the liquid crystal layer in a uniform layer thickness. The material of the spacer is resin, glass, etc., and its shape is a sphere or a cylinder.
The diameter is several μm to several tens of μm.

In order to fabricate a normal liquid crystal display cell, spacers having the same diameter as the liquid crystal layer thickness to be controlled are selected, and the spacers are evenly distributed at a constant density on one side of the substrates. And stick together. Then, liquid crystal is injected into the gap between the two substrates, and the injection port is sealed with an adhesive. Epoxy adhesives are often used as adhesives for bonding and sealing the injection port.

[0006]

As a method for distributing spacers on a substrate for keeping a liquid crystal layer in a uniform thickness, spacer particles are dispersed in a highly volatile solvent and sprayed. Method, the spacer is charged,
There is a method of repelling spacers having the same potential and adsorbing them on a substrate having a potential difference with respect to the spacers.

However, some spacers may be aggregated and aggregated in the liquid crystal display part. When the spacers are sprayed together with the solvent, residues other than the spacers may remain on the liquid crystal display portion on the surface of the substrate. These are non-uniform defects in the liquid crystal display unit, which deteriorates the display quality,
It also causes abnormal alignment of liquid crystal molecules around the spacer.
In particular, in the case of a projection type display using an SLM, the liquid crystal display unit is enlarged and projected, so that the image of the spacer becomes missing dots of the projected image, which causes a reduction in the image contrast ratio and a reduction in the resolution. This is an SLM corresponding to each RGB color
It becomes remarkable when the image according to is overlapped on the screen to form a color image.

An object of the present invention is to prevent such image defects from occurring and to make the thickness of the liquid crystal layer of the SLM uniform over the entire display portion to provide an SLM having good display quality.

[0009]

In order to prevent image defects caused by spacers or residues other than the spacers, the present inventor distributes the spacers only around the display portion.
Also, in order to keep the thickness of the liquid crystal layer uniform over the entire display area, it is necessary to keep the deflection of the substrate to a minimum,
The present invention has been accomplished.

That is, according to the present invention, a first transparent substrate which is transparent to at least writing light and on which a first transparent electrode layer is formed, and a second transparent electrode layer which is transparent to at least reading light are formed. A second transparent substrate, a photoconductor layer sandwiched between the first and second transparent electrode layers, a light-shielding layer, a mirror layer and a liquid crystal layer as an electro-optical effect layer, and write light is applied to the photoconductor layer. In the optical writing type spatial light modulation element, which is incident and modulates the reading light incident on the liquid crystal layer and emits the modulated light according to the characteristic change of the photosensitive layer due to the writing light, Spacers for keeping the thickness constant are arranged so as not to exist in the display unit, and the thickness h of the second transparent substrate, which is a rectangular flat plate having a thickness h and a side length a × b, is expressed by : H ³ ≧ {12p (1-ν ² )} / {π ⁴ wE (1
It is a spatial light modulator having a value satisfying / a ² + 1 / b ² ) ² }.

Here, the amount of displacement of the central portion of the second transparent substrate when an external load p is applied to the second transparent substrate is w, and the Poisson's ratio and Young's modulus of the second transparent substrate are respectively ν. , E.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The periphery of a display portion of a liquid crystal layer of an SLM is sealed with an adhesive. In the present invention, spacer particles for uniformly maintaining the thickness of the liquid crystal layer are preliminarily uniformly mixed and mixed in the uncured adhesive, and the surface of the liquid crystal is sandwiched by a method such as screen printing or a dispenser. Apply to both or one peripheral area. The adhesive is cured by heat treatment or UV irradiation while the surfaces sandwiching the liquid crystal are overlapped and pressed with an appropriate pressure. Then, a void having a thickness corresponding to the spacer diameter is obtained, and the void is filled with liquid crystal.

As the spacer, commercially available ones for liquid crystal cells such as silica glass and resin can be used. The transparent substrate used for SLM is sputtering or CV.
Since a functional film is formed in multiple layers by the method such as D, a glass substrate is used in terms of strength and durability. Since the first transparent substrate in which functional films are laminated in multiple layers is bent due to film stress, for example, a transparent substrate with an area of 48 × 34 mm has a thickness of 8 mm.
And it is thick. On the other hand, the second transparent substrate does not have as many films laminated as the first transparent substrate, but it is necessary to prevent the second transparent substrate from being bent even if its own weight or external stress is applied. This is because the thickness of the liquid crystal layer becomes non-uniform when it is bent. Therefore, it is important to calculate the thickness that can keep the thickness of the liquid crystal layer uniform.

Therefore, a method of calculating the thickness of the second transparent substrate will be described below. FIG. 2 is a conceptual diagram showing that a rectangular plate having a length a, a width b, and a thickness h is simply supported on the periphery thereof, and that the general distributed load shown in Formula 1 causes the bending. The deflection amount w'of an arbitrary point on the xy plane of this rectangular plate is expressed by Equation 2. In the formula, D represents bending rigidity and is represented by Formula 3. Where E is Young's modulus, ν
Is the Poisson's ratio.

[0015]

[Equation 1]

[0016]

[Equation 2]

[0017]

(Equation 3)

Now, the deflection amount w at the center of the rectangular plate in FIG. 2 can be obtained by substituting x = a / 2 and y = b / 2 into equation 2 and by substituting equation 3 into equation 4 It is represented by. That is, the maximum deflection amount of the rectangular plate is the deflection amount w at the center of the plate, which is inversely proportional to the cube of the plate thickness h. By rewriting Equation 4, Equation 5 is obtained. Since the plate thickness h in Equation 5 is a limit value, when the rectangular plate is subjected to the distributed load p, the h is limited so that the deflection amount w at the center of the rectangular plate falls within a predetermined allowable range. It should be more than the value.

[0019]

(Equation 4)

[0020]

(Equation 5)

[0021]

1 is a schematic sectional view for explaining an SLM according to an embodiment of the present invention. Hereinafter, according to this embodiment, S
A method for manufacturing the LM will be described. The first transparent substrate 1 is a glass substrate, and the transparent electrode layer 1a is formed on one surface of the glass substrate. The transparent electrode layer 1a is a thin film of ITO (indium tin oxide) having a thickness of 0.1 μm formed by a high frequency sputtering method. On the other hand, similarly, on the second transparent substrate 2, a transparent electrode layer 2a, which is an ITO thin film having a thickness of 0.1 μm, is formed.

First, the thickness h of the second transparent substrate 2 is calculated. The material of the second transparent substrate 2 is glass, and the side length a is
= 48 mm, b = 34 mm, Poisson's ratio ν = 0.210, Young's modulus E
= 8220 kgf / mm ² . When the distributed load p applied to the second transparent substrate 2 is set to 100 gf / 100 mm ² , in order to obtain the modulation uniformity of the liquid crystal layer 6, the deflection amount w at the center of the second transparent substrate 2 is set to SLM. 1/2 of the wavelength of read light 300
It should be within × 10 ^-6 mm. By substituting the above numerical values into Equation 5, h = 3.2 mm is derived. Therefore,
When the thickness of the second transparent substrate 2 is 3.2 mm or more, the modulation uniformity of the liquid crystal layer is maintained.

A photosensitive layer 3 is formed on the transparent electrode layer 1a. The photoconductor layer 3 is formed of a plasma CVD method and has a thickness of 20 μm of amorphous silicon hydride (a-Si: H).
It is. In addition to this, as the photoconductor layer, amorphous hydrogenated silicon carbide (a-SiC: H) and amorphous hydrogenated silicon nitride (a-
SiN: H), amorphous hydrogenated silicon oxide (a-SiO:
H) and the like can also be used.

A light shielding layer 4 is formed on the photoreceptor layer 3.
The light shielding layer 4 is a 2.5 μm thick SiO ₂ —Cu cermet film formed by a high frequency sputtering method.
A dielectric mirror layer 5 is formed on the light shielding layer 4. The dielectric mirror layer 5 is formed of an SiO ₂ film and a T film by an electron beam evaporation method.
A total of 13 layers, each having a thickness of ¼ wavelength, alternately laminated with an iO ₂ film, are multilayer films having a total film thickness of about 1 μm, and the optical reflectance thereof is 99% or more.

The liquid crystal alignment layers 6a and 6b are provided so as to sandwich the liquid crystal layer 6. The liquid crystal alignment layer 6a is on the dielectric mirror layer 5, the liquid crystal alignment layer 6b is on the transparent electrode layer 2a, and both are baked at 150 to 180 ° C. for 1 hour after the polyimide solution is applied by spin coating. To form a film. The spin coating rotation speed is controlled so that the liquid crystal alignment layers 6a and 6b have a layer thickness of about 60 nm after firing. next,
The surfaces of the liquid crystal alignment layers 6a and 6b are rubbed. The rubbing processing conditions are selected by changing the number of rotations of the rubbing drum, the pressure in contact with the substrate, etc., depending on the type of rubbing cloth or liquid crystal. The rubbing direction is the alignment direction of the injected liquid crystals, and when the SLM is assembled,
The transparent substrates 1 and 2 are rubbed so that the rubbing directions form an angle of 45 ° with each other.

After the surface of each liquid crystal alignment layer is rubbed, the transparent electrode layer 2a and the liquid crystal alignment layer 6b are coated with
A thermosetting epoxy adhesive 7 mixed with the spacer 6c is applied by a screen printing method so as to surround the display portion, leaving only the liquid crystal injection port. The amount of the spacer 6c mixed in the thermosetting epoxy adhesive 7 is 300 to 40.
It is adjusted to be 0 pieces / mm ² . Further, the spacer having an optimum diameter can be selected according to the liquid crystal used.

The transparent substrate 1 on which each layer is formed and the transparent substrate 2 on which each layer is formed and to which the spacer-containing adhesive is applied are attached so that the liquid crystal alignment layers 6a and 6b face each other. Then, the transparent substrates are put into an oven while being pressed with an appropriate pressure, and at 90 ° C at 80 to 100 ° C.
The epoxy adhesive 7 is cured by the heat treatment for 1 minute. After the adhesive is hardened, the SLM is set in the vacuum bell jar together with the liquid crystal reservoir, and the pressure inside the liquid crystal cell becomes low as the vacuum bell jar is exhausted. When the liquid crystal inlet of the liquid crystal cell touches the liquid crystal reservoir, the liquid crystal is filled in the cell by the capillary phenomenon, and the liquid crystal layer 6 is formed.

After filling the liquid crystal, SLM from the inside of the vacuum bell jar.
Is taken out and the liquid crystal injection port is sealed with an ultraviolet curable adhesive. The sealing adhesive is preferably an ultraviolet curable adhesive rather than a heat curable adhesive in order not to damage the liquid crystal. After the sealing adhesive is sufficiently solidified, the SLM is placed in an oven and heated to a temperature equal to or higher than the clearing temperature of the liquid crystal and annealed to complete the SLM.

The liquid crystal used in the SLM of the present invention includes TN liquid crystal, STN liquid crystal, PDLC (polymer dispersed liquid crystal) and the like.

[0030]

As described above, in the SLM of the present invention, the spacers for controlling the thickness of the liquid crystal layer are not distributed in the display portion but localized in the display portion periphery and the transparent substrate is made sufficiently thick. . As a result, in an image projected using the SLM of the present invention, it is possible to avoid a decrease in contrast ratio due to agglomeration of spacers on the display portion, a decrease in resolution, defects due to misalignment of liquid crystal molecules, etc. It was possible to obtain excellent display quality.

Further, since the thickness unevenness of the liquid crystal layer due to the deflection of the substrate is suppressed, the liquid crystal layer can be uniformly modulated over the entire display portion, and good display quality can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a completed state of an SLM (spatial light modulator) according to an embodiment of the invention.

FIG. 2 is a conceptual diagram showing a state where a rectangular plate whose periphery is simply supported is bent under a distributed load.

[Explanation of symbols]

 1, 2 ... Transparent substrate 1a, 2a ... Transparent electrode layer 3 ... Photoconductor layer 4 ... Shading layer 5 ... Dielectric Mirror layer 6 ... Liquid crystal layer 6a, 6b Liquid crystal alignment layer 6c Spacer 7 Epoxy adhesive

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G02F 1/135 G02F 1/135

Claims (1)

[Claims] 1. At least transparent to writing light,
Between the first transparent substrate on which the first transparent electrode layer is formed, the second transparent substrate on which the second transparent electrode layer is formed, which is transparent to at least the reading light, and between the first and second transparent electrode layers. A photosensitive layer sandwiched between, a light-shielding layer, a mirror layer and a liquid crystal layer that is an electro-optical effect layer, write light is incident on the photosensitive layer, according to the characteristic change of the photosensitive layer by the write light, In a photo-writing type spatial light modulator that modulates read light incident on the liquid crystal layer and emits the modulated light, a spacer that keeps the thickness of the liquid crystal layer constant is arranged in the display unit. In addition, the second transparent substrate is a quadrangular flat plate having a thickness h and a side length a × b, and has a center portion of the second transparent substrate when an external load p is applied to the second transparent substrate. The displacement amount is w, and the Poisson's ratio of the second transparent substrate is , Young's modulus is ν and E, respectively, the thickness h of the second transparent substrate is expressed by the following formula: h ³ ≧ {12p (1-ν ² )} / {π ⁴ wE (1 /
A spatial light modulator having a value satisfying a ² + 1 / b ² ) ² }.