JPH0854630A - Liquid crystal light valve and projection type liquid crystal display device using the same - Google Patents

Abstract

PURPOSE:To obtain an optical writing type liquid crystal light valve having high resolution and high photosensitivity by specifying the pretilt angle of the liquid crystal molecules near the contact parts of the oriented films with liquid crystal layer of the liquid crystal light valve of an optical writing type consisting of transparent substrates making a pair, the oriented films formed on both transparent substrates and the liquid crystal layer formed between these oriented films to a specific range. CONSTITUTION:This liquid crystal light valve consists of the transparent substrate 1 which has at least a photoconductor layer 6 and light reflection layer 12 on electrode 4 and the transparent substrate 2 which has electrode 5 and making a pair with the transparent substrate 1, the oriented films 8, 9 which are formed on both transparent substrates 1, 2 and orient the liquid crystal molecules and the liquid crystal layer 11 which is formed by sealing liquid crystal between these oriented films 8, 9. The pretilt angle thetap of the liquid crystal molecules near the contact parts of the oriented films 8, 9 with liquid crystal layer 11 of such liquid crystal light valve of the optical writing type is specified to be in the range of 3 deg.<thetap<10 deg.. As a result, the specific dielectric constant in a dark state, in which the light from the writing light source is not made incident, is increased and the impedance of the liquid crystal layer in a dark state is made small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type liquid crystal display device,
The present invention relates to an optical writing type liquid crystal light valve used for an optical arithmetic unit, a wavelength converter and the like, and a projection type liquid crystal display device using the same.

[0002]

2. Description of the Related Art In recent years, conferences and the like using large screen displays have been actively held. Conventionally, a slide projector or an overhead projector has been used as a large-screen display, but in general, since the screen brightness of a projector is extremely dark, it is necessary to darken the entire room while using the projector. . For this reason, in order to see the screen of the projector in normal brightness, that is, in such a brightness that an object can be written and read in a room, high brightness of the screen is required.

As one method for solving such a problem, there is a method disclosed in Document 1 (US Patent: Patent No. 4,019,807).
Applicant Donald D.M. Boswell, Jan
Grinberg, Alexander D .; Jaco
bson, Gary D .; Myer Hughes
The Aircraft Company discloses a projection type liquid crystal display device using an optical writing type liquid crystal light valve.

The above-mentioned optical writing type liquid crystal light valve (hereinafter,
A general configuration example of a liquid crystal light valve) is shown in FIG. As shown in FIG. 7, the liquid crystal light valve 110 is
A liquid crystal layer 106 that modulates the readout light by a voltage change,
Light-reflecting layer 1 made of a dielectric material that reflects readout light
05, a light shielding layer 104 made of CdTe (cadmium telluride) that blocks the transmitted light from the light reflection layer, and light made of CdS (cadmium sulfide) that controls the voltage applied to the liquid crystal layer 106 by changing the impedance according to the intensity of the incident light. It is composed of a conductor layer 103, and has a sandwich structure in which these are sandwiched by a transparent substrate 101 such as glass on which a transparent conductive film 102 is formed. Although not shown, the transparent conductive film 102 and the light reflection layer 105 which are close to the liquid crystal layer 106 are
An alignment layer for aligning the liquid crystal is provided.

FIG. 8 shows an example of a projection type liquid crystal display device using the optical writing type liquid crystal light valve having the above structure. In this projection type liquid crystal display device, the light from the light source 120 is transmitted through the lens system 1.
Passing through the polarization beam splitter 121 via 22b,
It is incident on the liquid crystal light valve 110. The liquid crystal light valve is connected as a writing light source 126 to a CRT 125 via an optic fiber plate 124. Therefore, the image to be projected is written in the liquid crystal light valve 110 by the writing light source 126, is emitted as light modulated according to image information in the liquid crystal light valve 110, and is emitted, and the polarization beam splitter 1 is again emitted.
21 through the lens system 122a and the screen 123
Projected on.

Further, as one of display modes used in a liquid crystal light valve, reference 2 (William.
Bleha, Jan Grinberg, Alexan
der D.D. Jacobson and Gary
D. Meyr Hughes Aircraft Lab
oratories, Malibu, CA: SID'7
7 Digest P.P. 104) and other hybrid field effect modes (hereinafter referred to as HFE
Mode and abbreviation) are known.

In this HFE mode, the nematic liquid crystal having a positive dielectric anisotropy is in an oriented state twisted at 45 °, and when a voltage is applied to the liquid crystal layer, the liquid crystal molecules respond to the electric field to cause the substrate to respond. The incident light is tilted in the normal direction, and the incident light has its polarization direction rotated by the birefringence effect and reflection from the tilt and twist of the liquid crystal molecules. The light that has received this rotation passes through the polarization beam splitter, and the screen becomes bright. On the other hand, when no voltage is applied, due to the optical rotatory power of the liquid crystal, the light incident on the liquid crystal layer cannot be transmitted through the polarization beam splitter because the polarization direction at the time of incidence is retained even if reflected, so that an image is not projected. And the screen is dark.

Reference 3 (Rodney D. Ste)
rling, Robert D. Te Kolste,
Joseph M. Maggerty, Thomas
C. Borah, William P. Bleha H
ughes Aircraft Company, Ca
rlsbad, CA: SID '90 Digest
P. In the projection type liquid crystal display device disclosed in 327), a CRT is used as an image writing device for a liquid crystal light valve. Therefore, in this projection type liquid crystal display device, since the writing light source is a CRT, an image is written with a weak writing light and a projection image is read with a strong reading light.

[0009]

By the way, in recent years, the resolution of images has been improved by the next-generation media medium represented by high-definition, and the resolution of projection type liquid crystal display devices has also been improved. In order to increase the resolution of the liquid crystal light valve, it is necessary to increase the resistance of each layer forming the liquid crystal light valve. However, if the impedance ZM of an intermediate layer (hereinafter, simply referred to as an intermediate layer) between transparent substrates such as a dielectric mirror layer and a light shielding layer is increased, the intermediate state in the photo state where the writing light is incident becomes The divided voltage in the layer increases and the divided voltage to the liquid crystal layer decreases. Therefore, the liquid crystal light valve in which the impedance of the intermediate layer has a high resistance is in a state in which the liquid crystal cannot be efficiently driven by the weak writing light, that is, the so-called light sensitivity is poor. Therefore, increasing the resistance of the intermediate layer causes a fatal problem that the sensitivity of the liquid crystal light valve is lowered.

Therefore, in order to improve the photosensitivity of the liquid crystal light valve, it is conceivable to increase the light amount of the CRT which is a writing light source. However, if the light amount of the CRT is increased, blurring of picture elements will occur. There is a problem that the resolution of the image is reduced.

CdS used as the photoconductor layer in Document 1 is excellent in photoconductivity but contains cadmium, which is a harmful substance, and is not preferable in view of environmental problems. Therefore, hydrogenated amorphous silicon (hereinafter referred to as a-Si: H) is used as the photoconductive substance. Since a-Si: H has a higher dielectric constant than CdS, a-Si: H, which is a photoconductor layer, is required to obtain the impedance in a dark state in which writing light is not incident, which is equivalent to that when using CdS. It is necessary to increase the film thickness of. However, when the film thickness of the photoconductor layer is increased, the portion where the writing light is not absorbed during the photo is increased and the voltage loss portion is increased, which may cause a problem that the photosensitivity of the liquid crystal light valve is deteriorated.

Further, if the resistance of the intermediate layer or the like is increased, the ratio of the divided voltage applied to the liquid crystal layer in the dark state and the photo state becomes smaller. When this divided voltage ratio is small, it is necessary to drive the liquid crystal light valve using a liquid crystal display mode having a good steepness. As such a liquid crystal display mode having good steepness, for example, DAP (tilted vertical alignment: Deformation) described in the above-mentioned Document 3 is described.
for Aligned Phase) ECB (electrically controlled birefringence: Electrically Contro)
Led Birefringence (hereinafter, DA
There is a mode called P-type ECB).

Further, as a method of aligning liquid crystals in the above DAP type ECB mode, reference 4 (US Patent: Patent No.
5,011,267 Applicant Hughes Airc
SiOx disclosed in the Raft Company)
The two-step oblique vapor deposition method is followed by a surface treatment with a long-chain alcohol.

However, this method has the following drawbacks. In the oblique vapor deposition method, if the vapor deposition conditions such as vapor deposition angle, vapor deposition rate, vacuum degree, substrate temperature, and film thickness, liquid crystal substance, and vapor deposition substance are different, the pretilt angle of liquid crystal is also changed significantly. Further, when the substrate is large, various conditions such as the above vapor deposition angle cannot be equalized in the plane, and it is difficult to obtain a uniform tilted vertical alignment in a large area with good reproducibility.

Therefore, in the DAP type ECB mode,
It is not possible to make a liquid crystal light valve with a large panel size. In addition, it is extremely difficult to improve productivity because the substrate can be produced only in a small area.

[0016]

A liquid crystal light valve according to claim 1 has an electrode, a transparent substrate having at least a photoconductor layer and a light reflecting layer on the electrode, and an electrode. A photo-writing type liquid crystal light including a transparent substrate paired with a transparent substrate, an alignment film formed on both transparent substrates for aligning liquid crystal molecules, and a liquid crystal layer formed by enclosing liquid crystal between the alignment films. In the bulb, the pretilt angle θp of the liquid crystal molecules near the contact portion between the alignment film and the liquid crystal layer is 3 ° <
It is characterized by being in the range of θp <10 °.

A liquid crystal light valve according to a second aspect is the first aspect.
The liquid crystal light valve described above is characterized in that the photoconductor layer is formed of an amorphous semiconductor containing silicon as a main component.

The liquid crystal light valve of claim 3 is the same as that of claim 2.
Alternatively, in the liquid crystal light valve described in 3, the liquid crystal display mode of the liquid crystal layer is a mixed field effect mode.

According to another aspect of the projection type liquid crystal display device of the present invention, three writing image generating means for generating writing images corresponding to red, blue and green, and three primary color images are emitted in response to incidence of the writing image. A projection type liquid crystal display device comprising three optically writing type liquid crystal light valves, and projection means for respectively injecting red, blue and green primary color reading lights into the liquid crystal light valve and synthetically projecting these reflected lights The liquid crystal light valve according to claim 1, 2 or 3 is used as the liquid crystal light valve.

[0020]

According to the structure of claim 1, the pretilt angle θp of the liquid crystal molecules near the contact portion between the alignment film and the liquid crystal layer is 3 ° <.
Since it is in the range of θp <10 °, the relative permittivity in the dark state where the light from the writing light source is not incident can be increased, and as a result, the impedance of the liquid crystal layer in the dark state can be reduced.

As a result, the resolution and the photosensitivity which are originally in a trade-off relationship can be compatible with each other, so that the liquid crystal can be driven by the weak writing light while maintaining the high resolution. As a result, an optical writing type liquid crystal light valve having high resolution and high photosensitivity can be realized.

Further, since the liquid crystal light valve having high photosensitivity can be realized as described above, the writing light source can be made compact, and therefore, any application system using the liquid crystal light valve can be made compact.

According to the structure of claim 2, by using an amorphous semiconductor containing silicon as a main component for the photoconductor layer, the dielectric constant of the photoconductor layer can be made approximately the same as that of the liquid crystal layer. Therefore, it is possible to more effectively realize an optical writing type liquid crystal light valve having high resolution and high photosensitivity.

According to the third aspect of the invention, since the mixed field effect mode in which the parallel alignment is twisted at 45 ° is adopted as the liquid crystal display mode, the conventional TN mode can be achieved without increasing the number of special processes when forming the liquid crystal layer. The process for producing the liquid crystal device can be used as it is. As a result, the time and cost for manufacturing the liquid crystal light valve can be reduced.

According to the structure of claim 4, by using the liquid crystal light valve according to claim 1, 2 or 3, it is possible to provide a projection type liquid crystal display device having high resolution and high contrast.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS.

As shown in FIG. 1, a liquid crystal light valve LVA according to the present embodiment faces a glass substrate (transparent substrate) 1 having a transparent electrode 4 formed on the surface and a surface facing the transparent electrode (electrode) 4. A glass substrate (transparent substrate) on which an electrode (electrode) 5 is formed and an antireflection film 3 is formed on the other surface
A sandwich structure in which a photoconductor layer 6, a light-shielding layer 7, a dielectric mirror (light reflecting layer) 12, an alignment film 9, a liquid crystal layer 11, and an alignment film 8 are sequentially formed between the glass substrate 1 and the glass substrate 1, The spacer 1 is provided between the transparent electrode 4 and the counter electrode 5 to keep the distance between the transparent electrode 4 and the counter electrode 5 constant.
It is equipped with 0.10.

That is, the liquid crystal light valve LVA having the above structure
Then, the writing light 14 is incident on the photoconductor layer 6 through the glass substrate 1, the impedance of the photoconductor layer 6 is changed by the intensity of the incident light, the voltage applied to the liquid crystal layer 11 is controlled, and While changing the alignment state to modulate the incident light, the read light 13 is transmitted through the glass substrate 2 to the liquid crystal layer 1
The incident light is incident on No. 1 and is reflected by the dielectric mirror 12, modulated by the liquid crystal layer 11, and emitted from the glass substrate 2.

The liquid crystal light valve LVA is manufactured as follows. First, a transparent conductive film made of indium oxide (ITO) doped with tin is formed on the entire surface of the glass substrate 1 by the sputtering method, and the transparent electrode 4 is formed on the glass substrate 1.

Next, on the transparent electrode 4, as the photoconductor layer 6, amorphous silicon hydride (a-Si: amorphous semiconductor) is used.
H) Form a film. This a-Si: H film is a silane (S
iH ₄ ) gas and hydrogen (H ₂ ) gas are used as raw materials and are formed by plasma CVD (chemical vapor deposition). At this time, the gas pressure is 0.3 Torr and the substrate temperature is 280 ° C. The film thickness of this a-Si: H film is about 8 μm.

The photoconductor layer 106 has an aS
In addition to i: H, amorphous hydrogenated silicon carbide (a-SiC:
H) or amorphous hydrogenated silicon germanium (a-SiG
It is also possible to use e: H).

When an a-SiC: H film is used as the photoconductor layer, SiH ₄ gas, H ₂ gas and CH ₄ gas are mixed as a raw material at a ratio of 10: 1/20, and plasma CVD is used. To form. The gas pressure at this time is 0.2
Torr and the substrate temperature are 300 ° C. This a-Si
The thickness of the C: H film is about 7.5 μm.

As the photoconductor layer, a-SiGe: H is used.
When a film is used, SiH ₄ gas, H ₂ gas, and germane gas (GeH ₄ ) are mixed as a raw material at a ratio of 10: 1: 50 and formed by plasma CVD. At this time, the gas pressure is 0.3 Torr and the substrate temperature is 250 ° C.
The film thickness of the a-SiGe: H film is about 9 μm.

Then, on the photoconductor layer 6, a light-shielding layer 7 for blocking light incident on the photoconductor layer 6 from the liquid crystal layer 11 side described later is formed. The light-shielding layer 7 is formed by spin-coating a carbon-dispersed acrylic resin into a thin film and baking the film at 250 ° C. to have a film thickness of about 1 μm.

Then, a dielectric mirror 12 for reflecting the light incident on the photoconductor layer 6 from the liquid crystal layer 11 side is formed on the light shielding layer 7. In this dielectric mirror 12, a multilayer film made of titanium oxide (TiO ₂ ) and silicon oxide (SiO ₂ ) is formed by an electron beam evaporation method.

A fiber plate may be used for the glass substrate 1.

On the other hand, the counter electrode 5 is formed on the glass substrate 2 facing the glass substrate 1 by depositing a transparent conductive film made of ITO by a sputtering method. Further, an antireflection film 3 for preventing surface reflection of glass is formed on the side of the glass substrate 2 on which the reading light 13 is incident.

Next, the counter electrode 5 and the dielectric mirror 12
Alignment film on top (described in Table 1 below) (manufactured by Japan Synthetic Rubber Co., Ltd.)
Are thinned by spin coating and baked at 180 ° C. to form alignment films 8 and 9 having a film thickness of approximately 500 Å. Then, the alignment films 8 and 9 are subjected to an alignment treatment by rubbing. The rubbing direction at this time was a direction in which the alignment state of liquid crystal molecules was twisted by 45 °. That is, the liquid crystal layer 11 has a hybrid electric field effect (Hybrid).
It is driven in the Field Effect mode (hereinafter referred to as the HFE mode).

In the HFE mode, when a voltage is applied to the liquid crystal layer 11, the liquid crystal molecules respond to the electric field and tilt in the normal direction of the substrate, and the incident light comes from the tilt and twist of the liquid crystal molecules. The polarization direction rotates due to the birefringence effect and reflection. On the other hand, when no voltage is applied, due to the optical rotatory power of the liquid crystal, the light incident on the liquid crystal layer 11 retains the polarization direction when the light is reflected.

Further, the above glass substrates 1 and 2 are bonded together via the spacers 10 and 10 which also serve as seals, and liquid crystal A (described in Table 2 below) is vacuum-injected between the substrates, Subsequently, the liquid crystal layer 11 is formed by sealing, and the liquid crystal light valve LVA of this embodiment is configured.

Further, the liquid crystal light valve LVA having the above structure
In the above, as the alignment films 8 and 9, four types of alignment films having different pretilt angles are used and four types of liquid crystal light valves L are used.
VAa to liquid crystal light valve LVAd were prepared.

Table 1 shows the relationship between the alignment film used for the alignment films 8 and 9 and the pretilt angle. In Table 1, the pretilt angle θp (°) is the pretilt angle of liquid crystal molecules near the alignment films 8 and 9.

[0043]

[Table 1]

Further, the above liquid crystal light valves LVAa ...
In the liquid crystal light valve LVAd, three kinds of liquid crystal having a dielectric constant ε as shown in Table 2 below are used as the liquid crystal used in the liquid crystal layer 11 and the liquid crystal light valve LVBa is used.
Liquid crystal light valve LVBd, liquid crystal light valve LVCa
-A liquid crystal light valve LVCd was prepared.

[0045]

[Table 2]

However, all of the above liquid crystals were nematic liquid crystals manufactured by Merck.

Here, in the alignment films and liquid crystals shown in Tables 1 and 2, when the pretilt angle θp and the reflectance of the liquid crystal molecules near the contact portion between the alignment films 8 and 9 and the liquid crystal layer 11 are minimum. Measure the relationship with the relative permittivity ε _LCRmin of the liquid crystal,
The results are shown in Table 3 below. FIG. 2 shows the relationship between the pretilt angle θp and the relative permittivity ε _LCRmin .

[0048]

[Table 3]

As a result of the above, as shown in Table 3 and FIG. 2, when the pretilt angle θp becomes large, the relative permittivity ε _LCRmin becomes large in all the liquid crystals. In particular, it can be seen that the relative permittivity ε _LCRmin sharply increases when the pretilt angle θp is 3 °.

The liquid crystal light valve LVA is driven by first applying an AC voltage to the liquid crystal light valve LVA and controlling the voltage applied to the liquid crystal layer 11 by impedance switching of the photoconductor layer 6. .

In general, in order to increase the resolution of the liquid crystal light valve, it is necessary to increase the resistance of each layer forming the liquid crystal light valve. However, for example, the dielectric mirror 1
2. Impedance ZM of an intermediate layer (hereinafter simply referred to as an intermediate layer) between the glass substrates 1 and 2 such as the light shielding layer 7.
When the resistance is increased, the divided voltage in the intermediate layer increases and the divided voltage to the liquid crystal layer 11 decreases in the photo state where the writing light is incident. Therefore, the liquid crystal light valve in which the impedance of the intermediate layer has a high resistance is in a state in which the liquid crystal cannot be efficiently driven by the weak writing light, that is, the so-called light sensitivity is poor. Therefore, increasing the resistance of the intermediate layer causes a fatal problem that the sensitivity of the liquid crystal light valve is lowered.

Further, in order to improve the photosensitivity of the liquid crystal light valve, it is conceivable to increase the light amount of the writing light source. However, if the light amount is increased, bleeding of the picture element of the image generally occurs, and The problem of lowering resolution occurs.

Therefore, in a liquid crystal light valve, generally, there is a trade-off relationship between high resolution and high photosensitivity.

That is, in order to make the liquid crystal light valve LVA have high brightness and high resolution, for example, in the dark state where the writing light is not incident on the liquid crystal layer 11, in the photo state where the writing light is incident on the photoconductor layer 6, for example, 200 μw / cm ²
It is necessary to apply a voltage to the liquid crystal layer 11 with a weak writing light. It is assumed that the liquid crystal layer 11 has the minimum reflectance in the dark state and the maximum reflectance in the photo state in the applied voltage.

Therefore, in order to make the liquid crystal light valve LVA have high brightness and high resolution, the impedance of the photoconductor layer 6 in the dark state is Z _PCdark , and the impedance of the photoconductor layer 6 in the photo state is Z _PCphoto . If the impedance of the liquid crystal layer 11 in the dark state is Z _LCRmin and the impedance of the liquid crystal layer 11 in the photo state is Z _LCRmax ,

[0056]

[Equation 1]

[0057]

[Equation 2]

Must be

Further, each layer constituting the liquid crystal light valve LVA such as the liquid crystal layer 11 can be replaced with a parallel circuit of a resistance component R and a capacitance component C, respectively. The combined impedance Z of the parallel circuit is

[0060]

(Equation 3)

It is expressed as follows. Further, the electrode area is S, the film thickness is d, the vacuum permittivity is ε ₀ , the relative permittivity is ε _r , and the resistivity is ρ.
Then, the resistance component R and the capacitance component C are respectively

[0062]

[Equation 4]

Since it is expressed as

[0064]

(Equation 5)

It is expressed as

In the liquid crystal light valve, in order to achieve both high resolution and high photosensitivity, the impedances of the liquid crystal layer 11 and the photoconductor layer 6 are predetermined according to the above equations (1) and (2). It is considered necessary to make a balance of In particular, the glass substrate 1 and the glass substrate 2 are the causes of the decrease in photosensitivity associated with higher resolution.
Photoconductor layer 6 other than liquid crystal layer 11 and light-shielding layer 7 existing between
It is conceivable that the partial voltage of the liquid crystal layer 11 is lowered due to the higher resistance of the intermediate layer.

The following three types of methods can be considered as methods for increasing the divided voltage applied to the liquid crystal layer 11.

In order to increase the impedance of the photoconductor layer 6 in the dark, the film thickness of the photoconductor layer 6 is increased.

The photoconductivity of the photoconductor layer 6 is increased in order to lower the impedance of the photoconductor layer 6 during photo.

A liquid crystal having a large relative permittivity ε⊥ (relative permittivity of liquid crystal before voltage application) and a small Δε is used.

However, there are problems in terms of process and cost. Also, in, since a-Si: H is used, there is an upper limit to the photoconductivity.

From the above, it is understood that it is desirable to adopt the method of.

Therefore, as the liquid crystal having a large relative permittivity ε⊥ and a small Δε, the above (1), (2)
It is considered that the liquid crystal obtained by the equation (3), for example, the liquid crystal shown in Table 2 above is optimal at the present stage.

As the optimum liquid crystal conditions obtained from the equations (1), (2) and (3), the impedance Z _LCRmin of the liquid crystal layer 11 in the dark state is small, and the impedance Z _L of the liquid crystal layer 11 in the photo state is small. _{Large LCRmax} is required. Further, due to simulation or the like, at this stage, with respect to the intermediate layer such as the photoconductor layer 6 or the like, the dielectric constant ε _LCmin when the reflectance of the liquid crystal is minimum is 7 to 8 and the reflectance of the liquid crystal is maximum when the reflectance is maximum. It has been found that a dielectric constant ε _LCmax of 10-11 is required.

Further, in order to investigate the pretilt angle dependence of the photosensitivity of the liquid crystal light valve LVA produced by the above method, the writing light quantity-reflectance (PR) characteristic was measured.
The results will be described below. In this measurement, the liquid crystal light valve LVAa and the liquid crystal light valve LVAc, that is, the liquid crystal A shown in Table 2 was used for the liquid crystal layer 11, and the alignment film 8
9 used the alignment film a and the alignment film c shown in Table 1 2
Writing light amount-reflectance (P
-R) The characteristics were measured.

The above measurement results are shown in FIGS. 3 and 4.
Here, the P-R characteristic represents how the reflectance is changed by applying a voltage or threshold voltage that minimizes the reflectance obtained by the VR characteristic and changing the writing light amount. . Further, the writing light quantity required to reach 95% of the saturation is defined as the switching light quantity by increasing the writing light quantity.

As shown in FIG. 3, in the liquid crystal light valve LVAa having the pretilt angle θp of 1 °, it can be seen that the reflectivity gradually increases as the writing light amount is increased. The switching light quantity at this time is about 1
It was 000 μW / cm ² . On the other hand, as shown in FIG. 4, in the liquid crystal light valve LVAc having the pretilt angle θp of 5 °, it can be seen that as the writing light amount is increased, the reflectance sharply increases with a small writing light amount. The switching light quantity at this time is about 300 μW /
cm ² .

Therefore, it is understood that the pretilt angle θp is preferably 5 ° rather than 1 ° in order to obtain a so-called high-sensitivity liquid crystal light valve which can be driven by weak writing light.

Further, the resolution of the liquid crystal light valve LVAa and the liquid crystal light valve LVAc was measured. still,
The writing light quantity is the switching light quantity.

As a result, the liquid crystal light valve LVAa has a resolution of 35 linepair / mm and the liquid crystal light valve LVAc.
Resolution was 40 linepair / mm. Therefore, it was found that the pretilt angle θp of 5 ° was higher than 1 ° and the resolution was high while maintaining high photosensitivity.

From the above results, the switching light amounts of the liquid crystal light valves LVAa to LVAd using the liquid crystal A, the liquid crystal light valves LVBa to LVBa using the liquid crystal B and the liquid crystal light valves LVCa to LVca using the liquid crystal C are obtained. FIG. 5 shows the pretilt angle dependence of the.

It can be seen from FIG. 5 that the switching light amount decreases as the pretilt angle θp increases. Further, the switching light amount sharply decreases from the pretilt angle θp of 3 ° to 5 °. With this, in order to realize a highly sensitive liquid crystal light valve,
It can be seen that the pretilt angle θp is preferably 3 ° or more. When a polyimide film is used as the alignment film, the upper limit of the pretilt angle θp is about 10 ° because of the stability of the pretilt angle.

Therefore, in order to realize a highly sensitive liquid crystal light valve, the pretilt angle θp is 3 ° <θp <1.
It is desirable to satisfy the relationship of 0 °, preferably 5 ° <θp <10 °.

According to the present invention, the alignment film 8 such that the pretilt angle of the liquid crystal molecules near the contact portion between the liquid crystal layer 11 of the liquid crystal light valve LVA and the alignment films 8 and 9 is a high pretilt angle of 5 ° to 10 °. By using 9, it is possible to achieve both resolution and light sensitivity, which are originally in a trade-off relationship. As a result, an optical writing type liquid crystal light valve having high resolution and high photosensitivity can be realized.

Further, in the present invention, since a liquid crystal light valve having high photosensitivity can be realized, the writing light source can be made compact, and therefore, any application system using the liquid crystal light valve of the present invention can be made compact.

Further, as the liquid crystal display mode, the parallel alignment is set to 4
Since the HFE mode twisted at 5 ° is adopted, the conventional process for producing a TN mode liquid crystal device can be used as it is without increasing the process at the time of producing the liquid crystal layer 11, and the production is easy. Also, no new capital investment is required. Therefore, the manufacturing cost of the liquid crystal light valve can be reduced.

FIG. 6 shows an example of a projection system as a projection type liquid crystal display device composed of the liquid crystal light valve LVAc produced in this embodiment.

The above projection system is shown in FIG.
As shown in FIG. 5, the liquid crystal light valve LVAc is used as a TFT liquid crystal panel 22r, 22g, 22b as an image generating means.
Writing lamps 21r, 21g, 21b as writing light sources for displaying red, green, and blue images via the
It is configured to be connected to. The above-mentioned TFT liquid crystal panels 22r, 22g and 22b have their respective color signals (R.
The image formed by the TFT liquid crystal panel is written in the liquid crystal light valve LVAc by the light emitted from the writing lamps 21r, 21g, 21b. It is like this.

On the other hand, the above-mentioned projection system is provided with a read-out lamp 26 as a read-out light source, and the light emitted from this read-out lamp 26 passes through the lens system 27 and the filters 28 and 29 and the mirror 30. , And enters the polarization beam splitter 23 provided for each color signal. The light incident on the polarization beam splitter 23 is individually modulated according to the brightness level of the writing light, and each read image obtained by this is used as projection means such as the polarization beam splitter 23 and the lens system 24. Screen 25 by optical system 31
Is projected in a composite manner.

The image projected by the projection system having the above-described structure was good in high resolution and high contrast. Therefore, by using the liquid crystal light valve having the above configuration, it is possible to provide a projection type liquid crystal display device that can easily realize high-luminance, high-resolution and high-contrast projection display.

In addition to the projection type liquid crystal display device, the present invention can be applied to various applications within a range that does not impair the effects of the present invention.

[0092]

According to the liquid crystal light valve of the first aspect of the present invention,
As described above, a transparent substrate having an electrode and at least a photoconductor layer and a light reflecting layer on the electrode, a transparent substrate having an electrode and paired with the transparent substrate, and both transparent substrates A liquid crystal light valve of the optical writing type, which comprises an alignment film which is formed on a substrate and which aligns liquid crystal molecules, and a liquid crystal layer which is formed by enclosing liquid crystal between the alignment films, in a contact portion between the alignment film and the liquid crystal layer. The pretilt angle θp of liquid crystal molecules in the vicinity is
The configuration is in the range of 3 ° <θp <10 °.

As a result, the resolution and the photosensitivity, which are originally in a trade-off relationship, can be compatible with each other, so that it is possible to drive with a weak writing light while keeping the high resolution. As a result, an optical writing type liquid crystal light valve having high resolution and high photosensitivity can be realized.

Further, since a liquid crystal light valve with high photosensitivity can be realized, the writing light source can be made compact, and therefore, any application system using the liquid crystal light valve of the present invention can be made compact.

In the liquid crystal light valve of the second aspect of the present invention, the photoconductor layer is formed of an amorphous semiconductor containing silicon as a main component.

As a result, the dielectric constant of the photoconductor layer can be made approximately the same as that of the liquid crystal layer, so that it is possible to more effectively realize an optical writing type liquid crystal light valve with high resolution and high photosensitivity. It has the effect of being able to.

As described above, the liquid crystal light valve according to the third aspect of the present invention has a structure in which the liquid crystal display mode of the liquid crystal layer adopts the mixed field effect mode.

As a result, the conventional process for producing a TN mode liquid crystal device can be used as it is without increasing the number of processes when producing the liquid crystal layer.

Therefore, it is possible to reduce the cost for manufacturing the liquid crystal light valve.

The projection type liquid crystal display device according to the invention of claim 4 is
As described above, three writing image generating means for generating writing images corresponding to red, blue and green, and three optical writing type liquid crystal lights for emitting three primary color images in response to incidence of the writing image. A projection type liquid crystal display device comprising a valve and projection means for respectively injecting read lights of three primary colors of red, blue and green into the liquid crystal light valve and combining and projecting the reflected lights thereof. The liquid crystal light valve described in 1, 2, or 3 is used.

As a result, it is possible to provide a projection type liquid crystal display device having high resolution and high contrast.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal light valve according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a relative dielectric constant of liquid crystal and a pretilt angle of an alignment film.

FIG. 3 is a graph showing the relationship between the writing light amount and the reflectance in the liquid crystal light valve according to the present invention.

FIG. 4 is a graph showing the relationship between the writing light amount and the reflectance in the liquid crystal light valve according to the present invention.

FIG. 5 is a graph showing the pretilt angle dependence of the switching light amount of a liquid crystal light valve.

FIG. 6 is a schematic configuration diagram of a projection type liquid crystal display device using the liquid crystal light valve of the present invention.

FIG. 7 is a cross-sectional view of a conventional liquid crystal light valve.

8 is a schematic configuration diagram of a projection type liquid crystal display device using the liquid crystal light valve shown in FIG.

[Explanation of symbols]

 1 glass substrate (transparent substrate) 2 glass substrate (transparent substrate) 4 transparent electrode (electrode) 5 counter electrode (electrode) 6 photoconductor layer 8 alignment film 9 alignment film 11 liquid crystal layer 12 dielectric mirror (light reflection layer)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihisa Hatano 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Co., Ltd. Within the corporation

Claims (4)

[Claims] 1. A transparent substrate having an electrode and having at least a photoconductor layer and a light reflecting layer on the electrode, and an electrode.
A photo-writing type liquid crystal comprising a transparent substrate paired with the above transparent substrate, an alignment film formed on both transparent substrates for aligning liquid crystal molecules, and a liquid crystal layer formed by enclosing liquid crystal between the alignment films. In the light valve, the pretilt angle θp of liquid crystal molecules in the vicinity of the contact portion between the alignment film and the liquid crystal layer is in the range of 3 ° <θp <10 °. 2. The liquid crystal light valve according to claim 1, wherein the photoconductor layer is formed of an amorphous semiconductor containing silicon as a main component. 3. The liquid crystal light valve according to claim 1, wherein the liquid crystal display mode of the liquid crystal layer is a mixed field effect mode. 4. Three writing image generating means for generating writing images corresponding to red, blue and green, and three optical writing type liquid crystal lights for emitting three primary color images in response to incidence of the writing image. Red on the bulb and the liquid crystal light bulb above,
A liquid crystal light valve according to claim 1, 2 or 3, wherein the liquid crystal light valve comprises a projection means for projecting read lights of three primary colors of blue and green and combining and projecting the reflected lights. A projection type liquid crystal display device characterized by using.