JP2647779B2 - Spatial light modulator and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spatial light modulator used for a projection type display and a method of manufacturing the same.

[0002]

2. Description of the Related Art At present, three types of projection type display are being developed.
There are different approaches. Among them, a projection type display using a cathode ray tube has a limitation in the brightness of the cathode ray tube and has a drawback that the device becomes large, so that there is a limit in increasing the area of the display. In addition, in the case of a liquid crystal projection display comprising a liquid crystal panel having a thin film transistor array, the resolution of the liquid crystal panel is insufficient, the aperture ratio of the liquid crystal panel is low, and the light resistance of the thin film transistor array made of an amorphous silicon thin film. Is low.

[0003] For this reason, a projection display in which a spatial light modulator, a small display, and a light source are incorporated in an enlarged projection optical system is expected to be promising. In this method, a weak image is once written on a spatial light modulator, another read light is modulated according to this write information, and projected on a screen.

In such a type of display, a so-called liquid crystal light valve using a nematic liquid crystal for a light modulation layer is generally used. However, in this system, one of the P and S polarized light components of the read light phase-modulated by the liquid crystal layer passes through the polarizing beam splitter and is projected on the screen. For this reason, when the readout light is in a random polarization state, 50% or more of the light is absorbed by the polarizing beam splitter. For this reason, the utilization rate of the reading light decreases, and the beam splitter generates heat.

As a method for solving this problem, a polymer-dispersed liquid crystal (PDLC) has recently been proposed.
A new liquid crystal light valve using the light scattering phenomenon of uid Crystal) has been proposed. PDLC is a liquid crystal material obtained by dispersing liquid crystal particles in a transparent polymer such as acrylic, and only a few years have passed since research began. In such a new type of liquid crystal light valve, transmission or scattering of the readout light is selected by the applied voltage applied to the PDLC, so that a polarizing beam splitter is unnecessary and the light utilization is high. Further, since it is not necessary to provide alignment layers on both side surfaces of the liquid crystal layer, it is easy to manufacture a large-area spatial light modulator. In addition, since birefringence is not used for light modulation, even if the thickness of the liquid crystal layer is uneven, the spatial uniformity of the readout light is not significantly affected.

[0006]

However, even when such a spatial light modulator is used, the readout light is still transmitted to the PD.
Irradiation is performed on the light modulation layer made of LC. Further, from the side opposite to the read light, write light is irradiated to the photoconductive layer. Therefore, the readout light must be reflected between the light modulation layer and the photoconductive layer so that the readout light does not leak to the photoconductive layer side.

For this purpose, it is known to provide a dielectric multilayer mirror between the photoconductive layer and the light modulation layer made of PDLC. However, the dielectric multilayer film is formed by stacking a large number of dielectric films having different refractive indices, and the reflectance is at most about ninety-nine to ninety-nine percent. Since the reading light has a much higher light intensity than the writing light, if even a small part of the reading light leaks to the photoconductive layer side, the photoconductive layer is exposed to light and its resistance decreases. Therefore, in order to improve the intensity ratio (amplification rate) of the read light to the write light, the read light transmitted through the dielectric multilayer film must be effectively blocked between the photoconductive layer and the light modulation layer. No.

An object of the present invention is to provide a spatial light modulation device comprising a transparent electrode and a light modulation layer made of a liquid crystal material for modulating the intensity, phase or traveling direction of readout light according to an applied voltage. The purpose is to effectively block read light from the light modulation layer.

[0009]

The present invention comprises a photoconductive layer,
One transparent electrode film provided on one surface of the photoconductive layer, a light shielding layer provided on the other surface of the photoconductive layer, and a dielectric multilayer film provided on the light shielding layer; A spatial light modulator including at least a light modulation layer provided on a dielectric multilayer film and another transparent electrode film provided on a surface of the light modulation layer, wherein the light modulation layer has an applied voltage. The light-shielding layer is formed of a liquid crystal material that modulates the intensity, phase or traveling method of the readout light according to the following conditions.
The present invention relates to a spatial light modulator which is an amorphous film substantially composed of 7.5 atomic% of silicon.

As a liquid crystal material, a nematic liquid crystal, a cholesteric liquid crystal, a smectic liquid crystal, and PDLC are preferable. The photoconductive layer is preferably formed of B ₁₂ SiO ₂₀ single crystal, B ₁₂ GeO ₂₀ single crystal, or GaAs single crystal. Alternatively, the photoconductive layer is preferably formed of a GaAs film, a hydrogenated amorphous silicon film, a hydrogenated amorphous silicon carbide film, or an amorphous selenium film.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A manufacturing process of a spatial light modulator 12A according to an embodiment of the present invention will be described step by step with reference to FIGS. In this embodiment, as the photoconductive layer 1A, Bi ₁₂ SiO ₂₀
A single crystal or a Bi ₁₂ GeO ₂₀ single crystal is used.

First, the photoconductive layer 1A made of these single crystals
Is cut out from a single crystal wafer, and one transparent electrode film 2A is provided on one surface of the photoconductive layer 1A (FIG. 1). Then
As shown in FIG. 2, a light shielding layer 3 is provided on the other surface of the photoconductive layer 1A according to the present invention. The configuration and manufacturing method of the light shielding layer 3 will be described later. Next, as shown in FIG. 3, a dielectric multilayer film 4 is provided on the surface of the light shielding layer 3 by vapor deposition.

On the other hand, as shown in FIG. 4, the other transparent electrode film 2B is formed on the surface of the glass substrate 7. The dielectric multilayer film 4 and the transparent electrode film 2B are opposed to each other with a sealing material 5 including a spacer interposed therebetween. Dielectric multilayer film 4, transparent electrode film 2B
A flat space 6 is formed between the sealing material 5.

In this embodiment, a polymer dispersed liquid crystal (PDLC), which is a liquid crystal material obtained by dispersing liquid crystal particles in a transparent polymer, is used. As a specific manufacturing method, a mixture of an uncured nematic liquid crystal and a resin matrix is injected from an injection port, and the injection port is sealed and then cured as in the case of a conventional ordinary twisted nematic liquid crystal. As a result, a light modulation layer 8 made of PDLC is formed in the space 6 as shown in FIG.

There is also a manufacturing method that does not use a sealing material. That is, for example, a mixture of an uncured nematic liquid crystal and a resin matrix is supplied on a substrate provided with a transparent electrode, and then, a dielectric multilayer film and a photoconductive layer to which a transparent electrode is attached are superimposed, and irradiated with light or the like. It can also be cured. Of course, after that, a sealing material may be applied to the periphery to seal the periphery. According to this manufacturing method, the mixture of the uncured nematic liquid crystal and the resin matrix may be simply supplied by roll coating, spin coating, printing, coating with a dispenser, or the like, so that the injection step is simple and the productivity is extremely high. . In addition, a mixture of these uncured nematic liquid crystals and a resin matrix has adverse effects on the performance of the liquid crystal, such as ceramic particles for controlling the substrate gap, plastic particles, spacers such as glass fibers, pigments, dyes, viscosity modifiers, and the like. Additives that do not contribute may be added.

Next, the operation of such a spatial light modulator will be described with reference to the configuration example of FIG. The writing light emitted from the weak writing light source 10A passes through the liquid crystal television 11 and becomes input image light. The input image light is condensed by the lens 13A and is irradiated on the spatial light modulator 12A. This input image light passes through the transparent electrode film 2A and enters the photoconductive layer 1A. On the other hand, a high-luminance readout light source 10
The reading light emitted from B is collected by the lens 13B,
The light is reflected by the mirror, adjusted by the lens 13C, and enters the light modulation layer 8.

Next, the incident light is mainly reflected by the dielectric multilayer film 4, passes through the light modulation layer 8 once again, is condensed by the lens 13C, and is projected on the screen 14 through the lens 13D.

The writing light is illuminated by the liquid crystal television 11. In a portion of the photoconductive layer 1A that is not exposed to light, the voltage applied between the pair of transparent electrode films 2A and 2B is mostly concentrated on the photoconductive layer 1A. Therefore, the voltage applied to the light modulation layer 8 does not reach the threshold voltage of the light modulation layer 8. On the other hand, when the light shines on the photoconductive layer 1A, the electric resistance of the photoconductive layer 1A is greatly reduced at that portion, and the voltage distributed to the light modulating layer 8 is increased and exceeds the threshold value.

Inside the light modulation layer 8 made of PDLC,
When no voltage is applied to the light modulation layer 8, the liquid crystal molecules are arranged along the interface between the polymer and the liquid crystal. The shape of the liquid crystal particles is random. When the voltage applied to the light modulation layer 8 is low, the refractive indices of the liquid crystal particles and the polymer are significantly different.
The reading light changes its traveling direction many times in the light modulation layer 8 and is scattered. On the other hand, when the voltage applied to the light modulation layer 8 exceeds the threshold voltage and the liquid crystal molecules are oriented in the direction of the electric field, the read light passes through the light modulation layer 8 without being scattered.

With such a mechanism, the two-dimensional intensity distribution in the input image light is converted into the two-dimensional intensity distribution in the readout light. If the intensity of the reading light is made higher than the intensity of the writing light, the signal amplification factor becomes higher accordingly.

As described above, the dielectric multilayer film 4 reflects only 90 to 99% of read light. For this reason,
Part of the reading light passes through the dielectric multilayer film 4 and the photoconductive layer 1A.
Leaks towards you. The more the intensity of the read light is higher than the intensity of the write light, the more the photoconductive layer 1A as described above
The light leaking to the direction becomes stronger, and the photoconductive layer 1A is exposed.

Therefore, in order to increase the signal amplification factor, it is necessary to provide the light shielding layer 3 for blocking the readout light passing through the dielectric multilayer film 4 between the photoconductive layer 1A and the dielectric multilayer film 4. . However, the light shielding layer 3 is required to have contradictory characteristics. That is, the light-shielding layer 3 must have a high readout light absorbing ability, thereby increasing the intensity of the readout light. However, the light-shielding layer having a high readout light absorbing ability usually remarkably lowers its specific resistance when light is absorbed. In such a case, the resolution of the spatial light modulator rapidly deteriorates, and the projected image becomes unclear.

Here, the present inventor has found a new light-shielding layer which can solve the above two trade-offs and can prevent the deterioration of the resolution of the element while increasing the intensity of the reading light. As a result, a bright, clear, and high-resolution projected image can be obtained. The light-shielding layer used in the present invention is an amorphous film substantially composed of 5 to 45 atomic% of germanium, 17.5 to 92.5 atomic% of carbon, and 2.5 to 77.5 atomic% of silicon. "Substantially" means that unavoidable impurities are acceptable.

More preferably, the composition of the elemental elements constituting the amorphous film is such that germanium is 12.5 to 35 atomic%. In order to form the light shielding layer 3, it is preferable to use a plasma chemical vapor deposition method (plasma CVD method) using a mixed gas of monosilane, germanium hydride, and methane or ethane. This is because the composition of the light-shielding layer can be appropriately changed by changing the flow rates of monosilane, germanium hydride, and methane (or ethane).

Next, an embodiment in which the photoconductive layer is a hydrogenated amorphous silicon film will be described with reference to FIGS. First, as shown in FIG. 7, one transparent electrode film 2A is provided on a glass substrate 17 whose surface is optically polished.

Next, as shown in FIG. 8, a photoconductive layer 1B made of a hydrogenated amorphous silicon film is provided on the surface of one transparent electrode film 2A, and a light shielding layer 3 is provided on the surface of the photoconductive layer 1B. After that, the dielectric multilayer film 4, the light modulation layer 8, the other transparent electrode film 2B, and the glass substrate 7 are provided according to the procedure described with reference to FIGS. Thus, the spatial light modulator 12B shown in FIG. 9 is obtained.

The photoconductive layer 1B made of a hydrogenated amorphous silicon film is preferably formed by plasma CVD. At this time, as described above, if the light shielding layer 3 is also formed by plasma CVD, the transparent electrode film 2A
The photoconductive layer 1B and the light-shielding layer 3 can be continuously formed on the same device by plasma CVD in the same device. Of course, at this time, it is necessary to appropriately change the material gas. The operation of the spatial light modulator 12B is the same as the operation of the element 12A described above.

Next, actual experimental results will be described. First, the component ratio of the amorphous film to be applied to the light-shielding layer of the present invention and the evaluation results will be described. An amorphous film having each component ratio as shown in the following table was formed by changing the partial pressure of the material gas. The film formation method is plasma C
The VD method was used. The material gas pressure was 50 mtorr, the discharge energy was 40 W, 15 W or 5 W, the substrate temperature was 100 ° C., and the film thickness was 1 μm. For each of these amorphous films,
The light transmittance was measured by a spectrophotometer, and the resistivity was measured by a two-terminal method. The composition ratio of each amorphous film was determined by quantitative analysis using an Auger electron spectrometer. The results are shown in Table 1 below. FIG. 10 shows a triangular diagram for the value of light transmittance, and FIG. 11 shows a triangular diagram for the value of resistivity.

[0029]

[Table 1]

In order to obtain a sufficient resolution, the resistivity must be 10
It is preferably at least ⁸ Ωcm, more preferably at least 10 ⁹ Ωcm.
On the other hand, in order to obtain the desired optical amplification,
It should be less than 10%, more preferably less than 3%. From the above results, it was found that the germanium content was particularly important. That is, the light transmittance is 10%
In order to reduce the content to 3% or less, the germanium content needs to be 5% or more and 12.5% or more. Further, in order to make the resistivity 10 ⁸ Ωcm or more, the germanium content is 45% or less, the silicon content is 2.5% or more, the carbon content is 17.5% or more, and the resistivity is 10 ⁹ Ωcm or more. In order to achieve this, it was necessary to make the germanium content 35% or less, the silicon content 5% or more, and the carbon content 2.5% or more.

Next, it was demonstrated how various changes in the components of the light-shielding layer affect the light amplification factor and the resolution of the spatial light modulator.

First, according to the procedure shown in FIGS.
A spatial light modulator 12A was manufactured. However, the photoconductive layer 1A is
Formed by Bi ₁₂ SiO ₂₀ single crystal, its dimensions are 35mm ×
35 mm x 0.5 mm. The transparent electrode films 2A and 2B were formed by a vacuum evaporation method. The light shielding layer 3 was formed by a plasma CVD method. This condition is as follows.

[Table 2] Material gas flow rate SiH ₄ 6.5 sccm GeH ₄ 1.6 sccm C ₂ H ₄ 29.5 sccm Material gas pressure 100 m torr Discharge energy 40 W Substrate temperature 100 ° C

The composition ratio of this amorphous film is as follows:
Atomic%, germanium was 19 atomic%, and silicon was 19 atomic%. This composition ratio was determined by quantitative analysis using an Auger electron spectrometer.

The dielectric multilayer film 4 was formed by a vacuum evaporation method. The dielectric multilayer film 4 is a laminate of a TiO ₂ thin film and a SiO ₂ thin film, and a total of 20 alternately stacked. Then, a PDLC was formed from the following materials to obtain a light modulation layer 8 having a thickness of 18 μm.

TABLE 3 (nematic liquid crystal) the long axis of the liquid crystal mixture ordinary refractive index n ₀ = 1.525 extraordinary refractive index n _e = 1.748 relative permittivity = 17.6 liquid crystal molecules in the long axis parallel to the direction of the liquid crystal molecules of cyanobiphenyl perpendicular Dielectric constant in direction = 5.1 (ultraviolet curable polymer) Urethane polymer Refractive index _np = 1.524 Curing wavelength range --- 350 to 380 nm (spherical spacer agent) Cured resin diameter ---------- 18μm

Then, the spatial light modulator 12A was incorporated into an optical system as shown in FIG. 6 and evaluated. In order to confirm whether or not a color moving image can be realized, a total of three elements 12A were manufactured and each of them was incorporated into the optical system shown in FIG. That is, the same spatial light modulation element 20 as the element 12A is used.
B, 20R, and 20G were fabricated and incorporated into the optical system of FIG. 12, respectively. In the optical system of FIG. 12, the liquid crystal panels 21B, 21B
The blue light is modulated by R and 21G, respectively, and each writing light is obtained.
22R, 22G, transmitted through the spatial light modulator 20B, 20R, 20G
Incident on. Thus, writing to each element is performed. On the other hand, the white light emitted from the white light source 23 is
Focuses on the mirror 25. Of the reflected light, blue light is reflected by the dichroic mirror 26B,
It is incident on 20B. Visible light other than blue light passes through the dichroic mirror 26B. Next, the red light is reflected by the dichroic mirror 26R and enters the element 20R. The green light passes through the dichroic mirror 26R and enters the element 20G.

Each of these primary color lights passes through the light modulation layer 8, is mainly reflected by the dielectric multilayer film 4, passes through the light modulation layer 8 again, and is projected on the screen 27 through the lenses 24B and 24C. You. Thereby, a full-color image is formed. The driving voltage of the spatial light modulator was 50 Vrms, the driving frequency was 30 Hz, the wavelength of the writing light was 380 to 490 nm, and the wavelength of the reading light was 400 to 490 nm. As a result, a write light intensity of 300 μW / cm ² and a read light intensity of 0.3 W / cm ² were realized, and the optical amplification factor was 1 × 10 ³ . The resolution at this time was 30 lp / mm.

In the above, a light-shielding layer was formed under the following conditions, and a spatial light modulator was prepared in the same manner as above except for the above.

Table 4 SiH ₄ 6.5 sccm GeH ₄ 1.6 sccm CH ₄ 40 sccm Gas pressure 50 mtorr Discharge energy 20 W Film pressure 3 μm The composition ratio of the amorphous film thus obtained is as follows: carbon 40%, germanium 50%, silicon 10%. there were. When the spatial light modulator was operated as described above, the image was very unclear, and only a resolution of 3 lp / mm was obtained.

In the above, a light-shielding layer was formed under the following conditions, and a spatial light modulator was manufactured in the same manner as above except for the above.

[Table 5] The composition ratio of the amorphous film thus obtained was 5% carbon, 0% germanium, and 95% silicon. And when this spatial light modulator was operated as described above, when writing light 50 μW / cm ² and reading light 500 μW / cm ² or more, light leaked to the photoconductive layer and image contrast was significantly reduced. Therefore, the reading light intensity could not be further increased. The optical amplification rate is about 10 times,
When projected on a large screen, only a dark image was obtained.

In the same manner as described above, the composition of the amorphous film constituting the light-shielding layer was variously changed, and the light amplification factor and resolution of the spatial light modulator were measured. The measurement results are shown together with the results already described.

[0040]

[Table 6]

As is apparent from these results, when the amount of germanium is 5 to 45%, the light amplification factor and the resolution of the spatial light modulator are good. In particular, this is 14%, 19%, 34%
At the time, the best characteristics were obtained. The amount of germanium is 4
At%, the resolution deteriorated extremely when trying to increase the optical amplification factor to 10 or more. In the example where the amount of germanium is 6%,
A relatively bright image was obtained. Germanium content is 44%
In the example of (1), a bright and relatively clear image was obtained. In cases where the amount of germanium exceeded 46%, only indistinct and blurred images were obtained.

[0042]

According to the present invention, a light shielding layer is provided between a photoconductive layer and a dielectric multilayer film, and the light shielding layer is formed of an amorphous film having the above composition. The readout light passing through the film can be effectively absorbed. Therefore, even if the intensity of the readout light is increased, the readout light is unlikely to leak to the photoconductive layer side, so that the photoconductive layer is less likely to be exposed to the readout light. This makes it possible to increase the magnification of the read light intensity with respect to the write light intensity. In addition, when an amorphous film having the above composition is used, even if a part of the readout light is absorbed, the resolution of the spatial light modulator is not deteriorated. it can.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state in which one transparent electrode film 2A is formed on the surface of a photoconductive layer 1A.

FIG. 2 is a cross-sectional view showing a state in which a light shielding layer 3 is provided on a photoconductive layer 1A.

FIG. 3 is a cross-sectional view showing a state in which a dielectric multilayer film 4 is provided on the surface of a light shielding layer 3.

FIG. 4 is a cross-sectional view showing a state in which a sealing material 5 is provided between a dielectric multilayer film 4 and another transparent electrode film 2B.

FIG. 5 is a sectional view showing a spatial light modulator 12A.

FIG. 6 is a schematic diagram illustrating an example of a projection optical system.

FIG. 7 is a cross-sectional view showing a state in which one transparent electrode film 2A is provided on the surface of a glass substrate 17.

FIG. 8 shows a photoconductive layer 1B and a light shielding layer 3 on the surface of a transparent electrode film 2A.
Is a cross-sectional view showing a state in which are sequentially provided.

FIG. 9 is a sectional view showing a spatial light modulator 12B.

FIG. 10 is a triangular diagram showing the relationship between the composition of the light shielding layer 3 and the light transmittance.

FIG. 11 is a triangular diagram showing the relationship between the composition of the light shielding layer 3 and the resistivity.

FIG. 12 is a schematic diagram illustrating an example of a full-color projection optical system.

[Explanation of symbols]

 1A, 1B Photoconductive layer 2A One transparent electrode film 2B The other transparent electrode film 3 Light shielding layer 4 Dielectric multilayer film 7, 17 Glass substrate 8 Light modulation layer made of liquid crystal material 12A, 12B, 20B, 20R, 20G Spatial light Modulator 14 Screen 21B, 21R, 21G LCD panel 23 White light source 26B, 26R Dichroic mirror

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yukihisa Osugi 3-9 Takeda-cho, Mizuho-ku, Nagoya-shi, Aichi, Japan No. 13, NGK Takeda-Kita Company House (72) Inventor Masaji Tange Ichioka, Mizuho-ku, Nagoya-shi, Aichi-ken 2-28, Chomachi, Gaishi-shi, Japan. JP-A-59-81627 (JP, A) JP-A-4-301819 (JP, A)

Claims (5)

(57) [Claims] 1. A photoconductive layer, one transparent electrode film provided on one surface of the photoconductive layer, a light shielding layer provided on the other surface of the photoconductive layer, and A spatial light modulator comprising at least a provided dielectric multilayer film, a light modulation layer provided on the dielectric multilayer film, and another transparent electrode film provided on the surface of the light modulation layer. The light modulating layer is formed of a liquid crystal material that modulates the intensity, phase or traveling direction of readout light in accordance with an applied voltage, and the light shielding layer is formed of 5-45 atomic% germanium and 17.5 atomic%.
A spatial light modulator, which is an amorphous film substantially composed of about 92.5 at% carbon and 2.5 to 77.5 at% silicon. 2. The light-shielding layer according to claim 1, wherein the light-shielding layer is an amorphous film substantially composed of 12.5 to 35 atomic% of germanium, 25 to 82.5 atomic% of carbon, and 5 to 62.5 atomic% of silicon. Spatial light modulator. 3. The light-shielding layer is an amorphous film formed by a plasma-enhanced chemical vapor deposition method using a mixed gas of monosilane, germanium hydride and methane.
The spatial light modulator according to any one of the preceding claims. 4. The light-shielding layer is an amorphous film formed by a plasma chemical vapor deposition method using a mixed gas of monosilane, germanium hydride, and ethane.
The spatial light modulator according to any one of the preceding claims. 5. When manufacturing the spatial light modulator according to claim 2, the light shielding layer and the photoconductive layer are continuously formed by plasma enhanced chemical vapor deposition in the same film forming apparatus. A method for manufacturing a spatial light modulator.