JPH0367247B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical writing type liquid crystal light valve element used in a projection type large screen display device or the like.

Optical writing type liquid crystal light valve elements are used in projection type large screen display devices and incoherent coherent light image conversion elements, which are input/output devices in optical image processing, and are used to convert optical input information into optical output information. It is a key device. An optical writing type liquid crystal light valve generally has a structure as shown in FIG. That is, on the first glass substrate 1, a transparent conductive film 2, an optical writing layer 3 made of a photoconductor film,
It has a structure in which a light shielding film 4 for separating input light 12 and output light 13 and a dielectric multilayer reflective film 5 are provided, and a display layer 8 made of liquid crystal is sandwiched between a glass substrate 6 having a second transparent conductive film 7. be. Here, 9 and 9' are alignment treatment layers made of insulating films for aligning liquid crystal molecules, 10 is a spacer, and 11 is a power source. The properties required for each part in this structure are as follows. First, the optical writing layer 3 made of a photoconductor has a dark conductivity of 10 ^-7 Ω ^-1 cm ^-1 or less and a bright conductivity of 10 ^-6 to 10 ^-4 Ω ^-1 cm ^-1
Next, the light shielding layer 4 has a bright conductivity of 10 ^-7 Ω ^-1 cm ^-1 or less and a large absorption coefficient, and the transmittance of the dielectric multilayer reflective film is 10% or less. The conductivity of the photoconductor is a value necessary to obtain high resolution and high contrast. In addition, the light-shielding film is originally not necessary if the transmittance of the dielectric multilayer reflective film is zero, but in order to obtain such a reflective film, strict film thickness control on the order of angstroms is required, and in practice it is not necessary. Such control is impossible. Therefore, in order not to impair the resolution, a light absorber with a bright conductivity of 10 ^-7 Ω ^-1 cm ^-1 or less is used to obtain a light shielding ability of 10 ^-4 to ^{10 -6} .

Conventionally, CdTe has been used as a material that satisfies the above conditions for CdS photoconductors, and for silicon crystal photoconductors, materials such as cermets containing large amounts of metals such as nickel and zinc in silicon dioxide have been used. Thin films have been used as light absorbers for blocking light. However, each of these substances is different,
Due to different manufacturing methods, mismatching of lattice constants between the photoconductor, the light-shielding layer, and the dielectric multilayer reflective film is likely to occur. Furthermore, since the CdS photoconductor has a long response speed of several milliseconds to several tens of milliseconds, it can be used for writing slide images, or CdS photoconductor has a relatively long afterglow property.
It is not suitable for high-speed scanning recording such as laser scanning recording where writing of one pixel takes several microseconds or less. These several drawbacks have resulted in the inconvenience that the liquid crystal light valve has a complicated structure, becomes an expensive device, and has limited applications.

An object of the present invention is to eliminate the drawbacks of the conventional optically writable liquid crystal light valve element described above, and to provide an optically writable liquid crystal light valve element that has a fast optical response speed, is easy to manufacture, and has good reproducibility of characteristics. It's about doing.

The optically writable liquid crystal light valve element of the present invention is a conventional optically writable liquid crystal light valve element in which the photoconductor film portion has a dark conductivity of 10 ^-7 Ω ^-1 cm ^-1 or less,
It is composed of an amorphous silicon film (a-Si:H) with a bright conductivity of 10 ^-6 to ^{10 -4} Ω ^-1 cm ^-1 or higher, and the light shielding film has a bright conductivity of 10 ^-7 Ω ^-1. An amorphous silicon film containing fluorine and hydrogen (a ^- Si:F:
H).

Hereinafter, the present invention will be explained with reference to the drawings.

In recent years, since it has been shown that the valence electrons of amorphous silicon can be controlled by erasing dangling bonds with hydrogen, applications of amorphous silicon in various fields have been actively researched. Due to its high dark resistance and photosensitivity, it has been considered to be applied to optically written liquid crystal light valve elements, but none has been put into practical use at present. The biggest reason for this is that a light shielding film material such as CdTe for CdS has not been found for amorphous silicon. The characteristics required for a light-shielding film are when exposed to projection light.
It must have a conductivity of 10 ^-7 Ω ^-1 cm ^-1 or less and a high absorption coefficient of 10 ⁴ cm ^-1 or more over the entire visible light range. The former is to ensure resolution, and the latter is to meet the requirements of high resistance, extremely low light sensitivity, and large absorption, which are the characteristics necessary to ensure a large ON-OFF ratio of the voltage applied to the liquid crystal. Furthermore, because there is no film that can be stably laminated on amorphous silicon, an optical writing type liquid crystal light valve using amorphous silicon has not been put into practical use.

On the other hand, research on the use of fluorine as a dangling bond terminator for amorphous silicon is being actively conducted. This is because the bonding energy of fluorine in silicon is greater than the bonding energy of hydrogen and silicon, and a thermally stable film may be obtained.

In our research, we discovered that films containing fluorine and hydrogen have a higher absorption coefficient than films containing only hydrogen. Furthermore, we believe that this film containing fluorine and hydrogen has a large absorption required for the light-shielding film, has high resistance, has a small increase in bright conductivity, and is a good match with an amorphous silicon film that only contains hydrogen. They found that the conditions were met and applied this to a liquid crystal light valve element.

First, the a-Si:H film used as the photoconductor film will be explained while showing its characteristics. FIG. 2 shows the dependence of the conductivity of an a-Si:H film formed by the glow discharge method on the substrate temperature during film formation.

In the figure, σ _D is the dark conductivity, and σ _P is the bright conductivity when irradiated with AMI (light with the same spectrum as sunlight and 100 mW/cm ² ). As is clear from the figure, the bright conductivity increases as the substrate temperature increases during film formation.
It spores at high temperatures above ℃. In addition, at temperatures above 200°C, the dark conductivity is below 10 ^-7 Ω -1 cm -1 and the bright conductivity is below 10 -7 Ω ^-1 cm ^-1 , which is necessary for the photoconductor film of an optically written liquid crystal light valve element.
It can be seen that the value of 10 ^-7 to ^{10 -4} Ω ^-1 cm ^-1 is fully satisfied.

By the way, the bright conductivity decreases when the substrate temperature is below 130℃.
10 ^-7 Ω ^-1 cm ^-1 or less, and it seems that this film can be used as a light-shielding film, but it is generally known that films formed at low temperatures are thermally unstable because hydrogen easily escapes, so it is not practical. It is not suitable for

Next, amorphous silicon containing fluorine and hydrogen satisfies the conditions as a light-shielding film under certain growth conditions, and can also be used as a photoconductor film if the conditions are changed, allowing continuous growth of the photoconductor film and light-shielding film. We show that this is possible and that a practical liquid crystal light valve element using amorphous silicon can be obtained.

Figure 3 shows a mixture of SiF ₄ and H ₂ with a conductivity σ of amorphous silicon (a-Si:F:H) produced by a glow discharge method using a mixed gas of SiF ₄ and H ₂ as a raw material gas. It shows ratio dependence. In the figure, σ _D is the dark conductivity, and σ _P is AMI (the spectrum is almost the same as that of sunlight).
It shows the bright conductivity when irradiated with light (with an energy density of 100 mW/cm ² ). The substrate temperature during growth is approximately 320°C and the pressure is approximately 1 Torr. As is clear from the figure, when the mixture ratio SiF ₄ /H ₂ is 30 or more, the bright conductivity is less than 10 ^-7 Ω ^-1 cm ^-1 , which indicates that the conductivity satisfies the conditions for a light-shielding film. Ru.

Furthermore, when SiF ₄ /H ₂ is around 10, the contrast ratio of conductivity is nearly six orders of magnitude, indicating that it can be used satisfactorily as a photoconductor film. FIG. 4 shows the dependence of conductivity on substrate temperature. From the figure, it can be seen that a high substrate temperature of 380° C. or higher is better for the photoconductive film.
It is also found that the lower the temperature, the lower the bright conductivity, making it suitable for a light-shielding film. In order to make such a good film, it is better to control the temperature, but since the film formation is performed in the order of the photoconductor film and the light-shielding film, the latter will be at a lower temperature, and the characteristics of each film will not be adversely affected. Fifth
The figure shows the dependence of the absorption coefficient α on SiF ₄ /H ₂ . According to the figure, the larger SiF ₄ /H ₂ is, the larger the absorption coefficient is, and it can be seen that SiF ₄ /H ₂ of about 30 sufficiently satisfies the conditions necessary for a light-shielding film. Therefore, in the glow discharge method, the substrate temperature is below 320℃ and the gas mixture ratio is
The light-shielding film can be obtained at a temperature of about 30° C. and a pressure of 1 Torr.

In this way, in the optically writable liquid crystal light valve element of the present invention, CdS was used as the photoconductor film and CdTe was used as the light shielding film, whereas CdS was used as the photoconductor film and CdTe was used as the light shielding film. and a-Si:F:H, both of which are characterized by the use of amorphous silicon. Therefore, the device of the present invention has the following advantages over conventional devices, such as improved characteristics and ease of manufacture.

(1) The optical response speed of a-Si:H is at least one order of magnitude faster than that of CdS, and a high-speed response optical writing type liquid crystal light valve element can be obtained.

(2) Physically, a-Si:H and α-Si:F:H are very similar materials, and there is no instability such as peeling phenomenon due to lattice mismatching.

(3) Continuous growth is possible at almost the same temperature, resulting in significant reductions in formation time and power savings.

(4) Because of continuous growth, the interface between the photoconductor film and the light-shielding film can be kept clean, and there is no deterioration of characteristics due to interface states.

(5) While CdS and CdTe are harmful substances, a
-Si is a non-polluting material.

Next, an embodiment of the present invention is shown in FIG.

In the figure, 14, 23 are glass substrates, 15,
22 is an ITO transparent electrode, 16 is a dark conductivity of 10 ^-7 Ω ^-1 cm ^-1 or less, prepared by glow discharge method using SiH ₄ as a raw material gas at a substrate temperature of 300°C and a pressure of 0.3 Torr;
a-Si:H film with a bright conductivity of about 10 ^-4 Ω ^-1 cm ^-1 , 17
is a-Si:F that was formed continuously by glow discharge method without taking out the sample from the forming apparatus under the conditions that the gas mixture ratio SiF ₄ /H ₂ of SiF ₄ and H ₂ was 30, the substrate temperature was 300°C, and the pressure was 1 Torr. :H film, the bright conductivity of this part is
10 ^-7 Ω ^-1 cm ^-1 or less. 18 is a conductive multilayer reflective film made by laminating cerium oxide and magnesium fluoride with a reflectance of 90% or more, and 19 and 19' are made by obliquely depositing SiO, with the liquid crystal molecular axes oriented horizontally to the substrate. Because twisted nematic mode liquid crystal is used, these layers are provided so that the directions in which the deposition source of oblique evaporation is viewed face each other and form an intersecting angle of 45°. Therefore, this alignment treatment layer gives the liquid crystal a 45° twist.
20 is a display liquid crystal, E7, 4-cyano-
4'-n-penterbiphenyl and 4-cyano-4'-
n-heptylbiphenyl and 4-cyano-4'-n-
0.25, 0.51, 0.1, respectively, ocmexibiphenyl and 4-cyano-4'-n-pentelterphenyl.
It is a mixed liquid crystal mixed at a ratio of 0.14 and operates in complex field effect twisted and nematic mode. Also, for 21, the spacer 24 is 1K~
An AC power supply of about 100KHz, 25 a writing light, and 26 a projection light.

The optically written liquid crystal light valve device obtained as described above could sufficiently follow laser light with a pulse width of about 1 μsec, confirming its high-speed performance. Furthermore, as described above, the photoconductor film and the light shielding film are obtained in a continuous shape.

As explained above, the optically writable liquid crystal light valve element of the present invention has a-Si:H or a-Si:
By using F:H for the photoconductor film and a-Si:F:H for the light-shielding film, elements can be formed easily using stable and non-polluting materials, and at high speed. It has many industrial advantages, such as:

[Brief explanation of drawings]

Figure 1 is a structural diagram of a general conventional optically writable liquid crystal light valve element, Figure 2 is a diagram showing the substrate temperature dependence of the conductivity of an a-Si:H film, and Figure 3 is a diagram showing the dependence of the conductivity of an a-Si:H film on the substrate temperature. :
A diagram showing the dependence of the conductivity of F:H on the gas mixture ratio SiF ₄ /H ₂ , Fig. 4 is a diagram showing the dependence of the conductivity on the substrate temperature in the a-Si:F:H film, and Fig. 5 is a -Si:
FIG. 6 is a diagram showing a change in the absorption coefficient of F:H depending on the gas mixture ratio SiF ₄ /H ₂ , and FIG. 6 is a diagram showing an embodiment of the optically writable liquid crystal light valve element of the present invention. In the figure, 1, 6... glass substrate, 2, 7...
...transparent electrode, 3...photoconductor film, 4...light shielding film,
5...Dielectric multilayer reflective film, 8...Liquid crystal, 9,9'
... Orientation treatment layer, 10 ... Spacer, 11 ...
Power supply, 12...Writing light, 13...Projection light, 14,
23...Glass substrate, 15,22...ITO electrode,
16... a-Si:F:H film for photoconductor, 17...
Light-shielding a-Si:F:H film, 18... Dielectric multilayer reflective film, 19, 19'... SiO alignment treatment layer, 20...
...Liquid crystal (E7), 21...Spacer, 24...
AC power supply, 25...writing light, 26...projection light.

Claims (1)

[Claims] 1. A transparent conductive film, a photoconductor film, a light shielding film, and a dielectric multilayer reflective film are laminated on a first glass substrate, and a second
In an optical writing type liquid crystal light valve element having a structure in which a liquid crystal is sealed between a glass substrate having a transparent conductive film, the photoconductor film has a dark conductivity of 10 ^-7 Ω ^-1
cm ^-1 or less, the light shielding film is composed of an amorphous silicon film having a bright conductivity of 10 ^-6 to 10 ^-4 Ω ^-1 cm ^-1 or more, and the light shielding film has a bright conductivity of 10 ^-7 An optically writable liquid crystal light valve element comprising an amorphous silicon film containing fluorine and hydrogen having a property of Ω ^-1 cm ^-1 or less. 2. The optically writable liquid crystal light valve element according to claim 1, wherein the amorphous silicon film constituting the photoconductor film is an amorphous silicon film containing hydrogen. 3. The optically writable liquid crystal light valve element according to claim 1, wherein the amorphous silicon film constituting the photoconductor film is an amorphous silicon film containing fluorine and hydrogen.