JPH06337434A - Spatial light modulating element - Google Patents

Abstract

PURPOSE:To obtain excellent display performance by reducing warping of a transparent substrate caused by a temperature change even if coefficients of thermal expansion of the transparent substrate and a light conductor of a spatial light modulating element are different from each other. CONSTITUTION:When a coefficient of thermal expansion of a light conductor 16 is small to a transparent substrate 20, the light conductor 16 side warps in a projecting shape as shown in (A) according to a temperature change. When an intermediate layer 50 having a coefficient of thermal expansion larger than that is formed on the transparent substrate 20, the intermediate layer 50 side warps this time in a recessed shape to the contrary as shown in (B). In this way, the relationship between a recess and a projection is reversed in response to the relationship of dimensions of the coefficient of thermal expansion. Thereby, when the intermediate layer 50 is formed between the transparent substrate 20 and the light conductor 16 as shown in (C), warping in the projecting direction of (A) and warping in the recessing direction of (B) are cancelled each other, and as a result, the warping is reduced.

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 having a photoconductor and a light modulator and used for optical information processing such as parallel processing of moving images and still images, its display, and storage. Specifically, it relates to improvement against thermal deformation.

[0002]

2. Description of the Related Art As a spatial light modulator used in a video projector or the like, there is one as shown in FIG. In the figure, a dielectric mirror 12, a light shielding layer 14, and a writing light incident side (arrow FA side) of the optical modulator 10,
The photoconductor 16, the transparent electrode 18, and the transparent substrate 20 are sequentially stacked. A transparent electrode 22 and a transparent substrate 24 are sequentially stacked on the read light incident side (see arrow FB) of the light modulator 10. An antireflection film is formed on each of the transparent glass substrates 20 and 24 on the light incident side from the outside as needed. The light shielding layer 14 is also provided as needed. A power supply 26 is connected to the transparent electrodes 18 and 22, and a driving voltage output from the power supply 26 is applied to the light modulator 10 and the photoconductor 16.

Of the above parts, the light modulator 10 has, for example, a structure in which a cell formed by a spacer 28 is filled with liquid crystal. A required liquid crystal alignment layer (not shown) is formed on the cell side of the dielectric mirror 12 and the transparent electrode 22. The dielectric mirror 12 is made of, for example, Si and Si.
It has a structure in which O ₂ (or TiO ₂ and SiO ₂ ) are alternately laminated a plurality of times by a method such as vapor deposition. Further, as the photoconductor 16, for example, a-Si: H (hydrogenated amorphous silicon) or a-SiC: H (hydrogenated amorphous silicon carbide) is used. Transparent electrode 18,
For example, ITO or SnO ₂ is used as 22.

Next, the operation of the above spatial light modulator will be described. An AC voltage is applied in advance between the transparent electrodes 18 and 22 by a power source 26. This applied voltage is applied to the light modulator 10, the dielectric mirror 12, the light shielding layer 14, and the photoconductor 16.
It is distributed to each layer according to the impedance of. In this state, when the writing light including the image information is incident on the spatial light modulator as indicated by the arrow FA, the writing light passes through the transparent glass substrate 20 and the transparent electrode 18 in order and reaches the photoconductor 16. . The photoconductor 16 absorbs the writing light and reduces its impedance. Then, the drive voltage distributed to the optical modulator 10 increases in accordance with the decrease in the impedance. That is, an electric field corresponding to the intensity distribution of the writing light is formed in the optical modulator 10.

In this state, when the read light is incident on the spatial light modulator as indicated by the arrow FB, the read light is transmitted through the transparent glass substrate 24 and the transparent electrode 22 in this order, and the light modulator 10 is read.
To reach. The read light is modulated by the birefringence of the liquid crystal or the like according to the write light intensity distribution, is further reflected by the dielectric mirror layer 12, and is output from the spatial light modulator as indicated by the arrow FC. In this way, the image information written in the spatial light modulator is read. The readout light is projected on a screen, for example. By using the spatial light modulator, it is possible to display an image with high brightness and high resolution. In particular, when a vertically aligned liquid crystal is used as the light modulator 10, it is possible to display an image with good contrast.

By the way, a-Si: H or the like used in the photoconductive layer body 16 of such a spatial light modulator is usually formed by a plasma CVD method. Japanese Patent Application No. 4-3355
The 96 patent application discloses a spatial light modulator having a thickness of about 10 to 30 μm.

[0007]

When a-Si: H or the like is formed on a transparent substrate in an amount of 10 to 30 μm, the temperature during film formation is as high as 200 to 250 ° C. Internal stress occurs due to the difference in thermal expansion coefficient between the transparent substrate 20 and a-Si: H. The internal stress causes a problem that the transparent substrate 20 that is flat before the film formation is warped after the film formation. If such a warp occurs, the thickness of the liquid crystal layer of the light modulator 10 formed thereafter becomes non-uniform, and the display performance deteriorates.

As a conventional technique for improving such a problem, the thickness of the transparent substrate 20 is increased. As the transparent substrate 20, a material having the same coefficient of thermal expansion as a-Si: H is used. There is a method of warping in advance (see Japanese Patent Application Laid-Open No. 3-261918).

However, according to the methods (1) and (2), even if the photoconductor is flat immediately after it is formed, the transparent substrate 20 still warps when the temperature changes during use as a spatial light modulator. Further, with the method (1), the coefficient of thermal expansion of the material that can be used as the transparent substrate 20 is limited, so that there is a disadvantage that a transparent substrate material having no distortion and uniform optical characteristics cannot be obtained.

The present invention focuses on these points,
A spatial light modulator that can obtain excellent display performance by reducing the occurrence of warpage due to temperature variation even when forming a photoconductor on a transparent substrate having a thermal expansion coefficient different from that of the photoconductor. The purpose is to provide.

[0011]

In order to achieve the above-mentioned object, the present invention provides a transparent spatial light modulator in which at least a photoconductor and a light modulator are laminated between transparent substrates with transparent electrodes. The thermal expansion coefficient of the substrate is α (SUB), the thermal expansion coefficient of the photoconductor is α (PC), and the thermal expansion coefficient of the intermediate layer is α.
(ML), they are α (PC) <α (SUB) <
An intermediate layer satisfying the relationship of α (ML) or α (PC)> α (SUB)> α (ML) is formed between the transparent substrate and the photoconductor.

[0012]

In the spatial light modulator according to the present invention, the transparent intermediate layer is provided between the transparent substrate on the photoconductor side and the photoconductor. Then, due to the action of this transparent intermediate layer, the internal stress due to the difference in thermal expansion coefficient between the transparent substrate and the photoconductor is relaxed. Thereby, the warp of the transparent substrate is reduced and the display performance of the spatial light modulator is improved.

FIG. 1 shows the basic operation of the present invention. The thickness of the transparent electrode is 500Å (0.05μ
m) to 2000 Å (0.2 μm), and does not warp the transparent substrate even if internal stress occurs due to temperature fluctuation, so the transparent electrode is omitted. For example, it is assumed that the photoconductor 16 has a smaller thermal expansion coefficient than the transparent substrate 20. Then, as shown in FIG. 4D, when the temperature reaches room temperature, the photoconductor 16 side warps so as to be convex. This state is shown in FIG. On the other hand, the intermediate layer 50 having a larger coefficient of thermal expansion than that on the transparent substrate 20.
If it is formed, this time, conversely, it warps so that the intermediate layer 50 side becomes concave. This state is shown in FIG.

As described above, the relationship of the unevenness when the temperature changes is reversed corresponding to the relationship of the coefficient of thermal expansion. Therefore, as shown in FIG. 7C, when the intermediate layer 50 is formed between the transparent substrate 20 and the photoconductor 16, the warp in the convex direction in FIG. The warp is just canceled, resulting in a flat state without warpage. Moreover, since it is flattened by the balance between the two,
For example, even if there is a change in temperature over time such as when the element is used for image projection, the warp of both elements is canceled and the element is favorably maintained flat.

When the magnitude relationship of the coefficient of thermal expansion is opposite to the case described above, that is, when the coefficient of thermal expansion of the transparent substrate 20 is smaller than that of the photoconductor 16, FIG. It becomes convex on the substrate side. In this case, the intermediate layer 5
If a material having a coefficient of thermal expansion smaller than that of the transparent substrate 20 is used as 0, the transparent substrate side is concave, as shown in FIG.
Therefore, similarly, it is possible to cancel the warp of both and obtain a flat element.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the spatial light modulator according to the present invention will be described in detail below with reference to FIG. The same reference numerals are used for the same components as those of the above-described conventional technique or components corresponding to the conventional technique.

As the transparent substrate 20, "7059 glass" manufactured by Corning Incorporated was used. Its thermal expansion coefficient α (SU
B) is 46 × 10 ⁻⁷ / ° C., and the size of the substrate itself is 24 mm × 38 mm and the thickness is 2 mm. On the other hand, the thermal expansion coefficient α of a-Si: H used as the photoconductor 16
(PC) is about 35 × 10 ^-7 / ° C. As the intermediate layer 50 for realizing the flattening, "BK-7 glass", which is transparent glass manufactured by Schott, was used. Its coefficient of thermal expansion α
(ML) is 80 × 10 ⁻⁷ / ° C. That is, the coefficient of thermal expansion has a relationship of α (PC) <α (SUB) <α (ML) …………………… (1).

Using the above materials, samples were prepared for the case where the intermediate layer 50 was not provided and the case where the intermediate layer 50 was provided, and the warpage was compared. The results are shown in FIGS. 2 and 4.

First, referring to FIG. 4, the intermediate layer 50
A conventional case in which the above is not provided will be described. First, tin-containing indium oxide (ITO) or the like is formed on the main surface of the transparent substrate 20 shown in FIG. 7A by a sputtering method or a vacuum deposition method to obtain the transparent electrode 18 (see FIG. 9B). ). Next, the photoconductor 16 of a-Si: H is formed in a thickness of 20 μm by the plasma CVD method (see FIG. 6C). Specifically, the substrate temperature is 200 ° C., the SiH ₄ gas is 15 sccm,
Film formation was performed under the conditions of H ₂ gas 60 sccm, gas pressure 133 Pa, and input power 20 W. After that, when the temperature reached about room temperature, due to the difference in thermal expansion coefficient between the photoconductor 16 and the transparent substrate 20, the photoconductor 16 side was warped so as to be convex as shown in FIG.

The flatness before forming the photoconductor 16 is 0.3 μm.
However, the flatness at room temperature after formation of the photoconductor 16 deteriorated to about 2 μm due to the generation of compressive stress. It should be noted that 200 after the photoconductor 16 was formed.
Since the flatness in the temperature state of 0 ° C. was 0.3 μm or less, no true stress was generated under the film forming conditions of the photoconductor 16, and only the thermal stress due to the difference in the thermal expansion coefficient was used for flattening. I found that you should consider.

Next, the case where the intermediate layer 50 is provided will be described with reference to FIG. In this case, the transparent substrate 20
BK-7 glass is formed by a sputtering method or a vacuum evaporation method (see (A) of the same figure) to obtain an intermediate layer 50 (see (A1) to (D1) of the same figure). At this time, the thickness of the intermediate layer 50 is 1 μm in the same figure (A1), 3 μm in the case of (B1), and (C
Samples were obtained by changing 1) to 5 μm and (D1) to 10 μm. The substrate temperature at the time of forming this intermediate layer is the same as that at the time of forming a-Si: H, 200 ° C.
And

Next, the transparent electrode 18 is formed on the intermediate layer 50 under the same conditions as in FIG.
2) to (D2)), and a photoconductor 16 made of a-Si: H was formed thereon (see (A3) to (D3) in the same figure). For each of these samples, the flatness of the device at room temperature after the film formation was examined.
As shown in (D4).

First, in the thinnest sample having the intermediate layer 50 of 1 μm, a warp of about 1.5 μm occurred in the convex shape (the transparent substrate side is concave) as shown in FIG. Next, in the sample with the intermediate layer 50 having a thickness of 3 μm, a warp was generated in a convex shape as shown in FIG. 4B, but the degree of warpage was smaller than that of the sample in FIG. It was Next, in the sample with the intermediate layer 50 of 5 μm, the same figure (C4)
As shown in (1), almost no warp was observed, and it was 0.3 μm or less. Next, in the sample in which the intermediate layer 50 had a thickness of 10 μm, a warp of about 2.0 μm in a concave shape (convex on the transparent substrate side) occurred in the opposite direction as shown in FIG.

From these results, when the thickness of the intermediate layer 50 is thin, compressive stress is generated as in the case where the intermediate layer of FIG. 4 is not provided. On the other hand, the intermediate layer 50
When the film thickness is 5 μm, the stress is canceled and almost zero
It can be seen that, when the intermediate layer 50 is further thickened, tensile stress is generated.

Thus, according to the results of this embodiment,
By controlling the thermal expansion coefficient and the thickness of the intermediate layer 50, it is possible to reduce the internal stress caused by the temperature change, and even if the transparent substrate 20 and the photoconductor 16 have different thermal expansion coefficients,
A good element substrate with no warp can be obtained. Therefore, the liquid crystal layer in the light modulator 10 does not have thickness unevenness, and the display uniformity is improved. Further, as described with reference to FIG. 1, the warp generated between the transparent substrate 20 and the photoconductor 16 and the warp generated between the transparent substrate 20 and the intermediate layer 50 are canceled, so that it is used. The flatness is maintained even when the temperature changes, and the driving temperature stability is improved.

In order to obtain the spatial light modulator of FIG. 3, on the photoconductor 16 of FIG. 2 (C4) obtained as described above,
The light shielding layer 14 and the dielectric mirror 12 are sequentially formed. Then, after performing the alignment treatment on the liquid crystal, another transparent substrate 24 with the transparent electrode 22 and the transparent substrate 20 are bonded together to form a cell. Then, liquid crystal is injected between the cells to obtain a spatial light modulator.

<Other Embodiments> The present invention is not limited to the above embodiments, and includes, for example, the following ones. (1) In the above embodiment, the coefficient of thermal expansion α (SU
The case where B) is larger than the thermal expansion coefficient α (PC) of the photoconductor 16 has been described, but the relationship may be reversed depending on the material used. In this case, the relationship with the coefficient of thermal expansion α (ML) of the intermediate layer is α (PC)> α (SUB)> α (ML) ………………………… (2) Good. (2) In the above embodiments, only the relationship between the transparent substrate and the photoconductor is dealt with, but the intermediate layer may be formed in consideration of the thermal expansion coefficient of the light shielding layer or the dielectric mirror.

(3) In the above embodiments, "7059 glass" manufactured by Corning Co., Ltd. was used as the transparent substrate 20, and "BK-7 glass" manufactured by Schott Co. was used as the intermediate layer 50. Materials may be used. Also,
As a method of forming each layer, another method such as a vacuum vapor deposition method, a sputtering method, a plasma CVD method may be appropriately used. In this case, the relationship of the coefficient of thermal expansion of each layer should satisfy the above formula (1) or formula (2).

[0029]

As described above, according to the spatial light modulator of the present invention, the intermediate layer is formed between the transparent substrate and the photoconductor, and the relationship of the thermal expansion coefficient of these layers is α ( P
C) <α (SUB) <α (ML) or α (PC)> α (SU
Since B)> α (ML), even if the thermal expansion coefficient of the transparent substrate and that of the photoconductor are different, the internal stress generated due to temperature fluctuations is mitigated to improve the flatness of the substrate. There is an effect that it is possible to obtain an excellent display performance.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an operation of flattening a substrate in a spatial light modulator according to the present invention.

FIG. 2 is an explanatory diagram showing a forming procedure and a state of warpage according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a configuration of a general spatial light modulator.

FIG. 4 is an explanatory diagram showing a procedure of forming each layer and a state of warpage in a conventional case in which an intermediate layer is not provided.

[Explanation of symbols]

10 ... Light modulator, 12 ... Dielectric mirror, 14 ... Light-shielding layer,
16 ... Photoconductor, 18, 22 ... Transparent electrodes, 20, 24 ...
Transparent substrate, 26 ... Driving power supply, 28 ... Spacer, 50 ... Intermediate layer, FA ... Incident direction of writing light, FB ... Incident direction of reading light, FC ... Output direction of reading light.

Claims (1)

[Claims] 1. A spatial light modulator in which at least a photoconductor and a light modulator are laminated between transparent substrates with transparent electrodes, wherein the coefficient of thermal expansion of the transparent substrate is α (SUB), The coefficient of thermal expansion is α (PC), and the coefficient of thermal expansion of the intermediate layer is α
(ML), they are α (PC) <α (SUB) <
A spatial light modulation element, characterized in that an intermediate layer satisfying the relationship of α (ML) or α (PC)> α (SUB)> α (ML) is formed between the transparent substrate and the photoconductor.