JPH0323426A - Liquid crystal light valve - Google Patents

Abstract

PURPOSE:To obtain a high contrast with easy production by constituting a liquid crystal driving circuit of a voltage dividing circuit consisting of a photoconductor and a resistor having no photosensitivity with the same shape as the shape of this photoconductor. CONSTITUTION:The liquid crystal driving circuit is constituted of the voltage dividing circuit consisting of the photoconductor 101 and the resistor 102 having no photosensitivity with the same shape as the shape of this photoconductor 101. The voltage change applied on the liquid crystal 103 can, therefore, taken as larger as the voltage resistance of the voltage dividing circuit permits. The high contrast is obtd. in this way and the film thickness which is the constituting element of a liquid crystal light valve is small and, therefore, the period for forming the multilayered films is extremely shortened. The production is thereby extremely facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical writing type liquid crystal light valve that is used for optical information processing and converts an optical signal into another optical signal.

[Conventional technology]

A liquid crystal light valve is a light modulation element used in a light projection type display, optical information processing, etc., and the one shown in FIG. 4 is known as an optical writing type device.

Figure 4(a) shows the structure of a liquid crystal light valve.
Opposing glass substrates 301 and 305 and transparent conductive film 4
01, 402, a photoconductive film 403 made of CdS (cadmium sulfide), a light absorption film 404 made of CdTe (cadmium telluride), and a multilayer reflective film 405 made of multiple layers of insulating films with different refractive indexes. , a liquid crystal 103 using TN liquid crystal, and a spacer 406.

In FIG. 4(a), reference numeral 106 indicates a writing light, and 107 indicates a reading light.

Further, FIG. 4(b) shows an equivalent circuit of the liquid crystal light valve constructed as described above, showing the equivalent capacitance 407 of the liquid crystal 103, the equivalent capacitance 408 of the multilayer reflective film 405, and the equivalent resistance of the light absorption film 404 made of CdTe. 409 and equivalent capacity it410
and the equivalent resistance 411 of the photoconductive film 403 made of CdS.
and equivalent appearance 412. That is, the equivalent resistance 409 and equivalent capacitance 410 of the light absorption film 404 are connected in parallel, and the equivalent resistance 411 and equivalent capacitance 412 of the photoconductive film 403 are connected in parallel, and the liquid crystal 103
The equivalent volume M407 of the multilayer reflective film 405 and the equivalent volume 140 of the multilayer reflective film 405
8, a parallel circuit of an equivalent resistance 409 and an equivalent capacitance 410 of the light absorption film 404, and an equivalent resistance 4 of the photoconductive film 403.
11 and a parallel circuit with an equivalent capacitance 412 are connected in series with each other as shown.

The operating principle of the device with the above structure is as follows. First, in the operating state, the transparent conductive films 401, 402
A constant alternating current voltage is applied to the liquid crystal 103, and a voltage divided by substantially equivalent capacitances 407, 408, 410, and 412 is applied to the liquid crystal 103. The reason is that each equivalent resistance 409. This is because the resistance of 411 is very high.

Now, as shown in FIG. 4(a), when the writing light 106 enters from the glass substrate 301 side, the resistance value of the CdS in the portion of the photoconductive film 403 that is hit by the light decreases. . That is, in the equivalent circuit shown in FIG. 4(b), the resistance of the CdS equivalent resistance 411 becomes smaller. Therefore, the equivalent capacitance 412 of CdS is almost short-circuited, and the equivalent capacitance i407 of the liquid crystal 103, that is, the voltage applied to the liquid crystal 103 increases. That is, as described above, the equivalent resistance of the photoconductive film 403 is
and the equivalent capacitance 412 are connected in parallel with each other, and on the other hand, the liquid crystal 103 has a pair of transparent conductive films 401 on both sides,
A constant alternating voltage applied to 402 is applied to each equivalent capacitance 40
7,408, 410. Since a voltage divided by 412 is applied, if the equivalent capacitance 412 is almost short-circuited, the voltage applied to the liquid crystal increases by that amount.

In the above device, the liquid crystal 103 is controlled by this voltage change to modulate the readout light 107. Note that the role of the light absorption film 404 is to direct the readout light 107 to the photoconductive film 40.
The goal is to not let it reach CdS, which is 3.

In this way, the liquid crystal light valve shown in FIG.
It can be used as a light modulation element used in optical information processing and the like.

[Problem to be solved by the invention]

However, this conventional liquid crystal light valve has at least the following two manufacturing and performance problems.

That is, one problem is that it is difficult and time-consuming to manufacture. As can be seen from the equivalent circuit shown in FIG.
It must be sufficiently small compared to the equivalent capacity 1n407 of 03. For this purpose, the CdS film must be sufficiently thick. However, it is not easy to make a thick CdS film.

Normally, the CdS film needs to have a thickness of 15 to 20 ξcm, and polishing between the layers is necessary to create a cloud-free film.

Conventionally, the film was usually formed by sputtering, and to form a film of this thickness,
It takes 10 to 20 hours including polishing.

In addition, it is necessary to form a CdTe film of about 2 microns and a multilayer insulating film. Therefore, it takes a considerable amount of time to complete one element.

Another problem, ie, the second problem, is that the dynamic range is narrow and it is not possible to obtain a large contrast.

As explained in the operating principle, the equivalent volume M40 of the liquid crystal 103
The voltage applied to 1 is the equivalent capacity 407, 408, 41
0. Since the voltage is divided by 412, even if the equivalent capacitance 412 of the photoconductive layer M403 changes greatly, the voltage applied to the equivalent capacitance 407 of the liquid crystal 103 does not change so much. Since the change in this voltage is small, the actual situation is that conventionally the display contrast is only about 5 to 8.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal light valve that is easy to manufacture and has high contrast by eliminating the drawbacks of the conventional light valves.

[Means for Solving the Problems] The present invention forms a one-dimensional or two-dimensional array-like liquid crystal drive circuit that performs a switching operation using light on a transparent insulating substrate, and forms a liquid crystal driving circuit on a transparent insulating substrate, and a transparent electrode-attached glass panel facing the transparent insulating substrate. A liquid crystal light valve having a liquid crystal sandwiched between the substrate and the liquid crystal drive circuit, wherein the liquid crystal driving circuit is constituted by a voltage dividing circuit consisting of a photoconductor and a resistor having the same shape as the photoconductor and having no photosensitivity. It is characterized by

[Function] In the liquid crystal light valve of the present invention, since the liquid crystal drive circuit is constituted by a voltage dividing circuit consisting of a photoconductor and a resistor having the same shape as the photoconductor and having no photosensitivity, the withstand voltage of the voltage dividing circuit is The voltage change applied to the liquid crystal can be made as large as possible. Therefore, it is possible to achieve high contrast.

Further, since the film thickness, which is a structural element of the liquid crystal light valve of the present invention, is thin, the forming period of the multilayer film is extremely short, and therefore manufacturing is extremely easy.

〔Example] Next, an example of the liquid crystal light valve of the present invention will be described.

FIG. 2 and FIG. 3 are diagrams showing one embodiment, and FIG.
The figure is a plan view, and FIG. 3 is a sectional view taken along line AA' in FIG. 2.

The structure of the liquid crystal light valve of this example will be explained together with its manufacturing process.

First, to form a light-shielding film 201 on a glass plate 301, which is a transparent insulating substrate, 1500 angstroms of chromium is sputtered and patterned as shown in FIG. This light-shielding film 201 is for forming a resistor that does not have photosensitivity and will be described later.

Next, silane (S i H4) and ammonia (NH.) are mixed and decomposed by glow discharge to form a silicon nitride film 302 of 3000 angstroms. The silane is continuously decomposed to remove 3000 angstroms of non-quality silicon. Furthermore, silane and phosphine (P
H3) is mixed and decomposed to form a film of 500 angstroms of n-type non-quality silicon 307 containing a large amount of phosphorus. This is for making ohmic contact with the electrode. This was patterned to form a photoconductor of 10l,
A resistor 102 is formed. At this time, if the photoconductor 101 and the resistor 102 have the same shape as shown in FIG. 2, they will have approximately the same resistance value.

Next, a film of 500 angstroms of chromium and 3000 angstroms of aluminum is successively formed by sputtering and patterned to form the output electrode 108 and the electrode 104. Further, the n-type non-quality silicon 307 is removed by etching.

Next, an interlayer insulating film of silicon nitride 303 having a thickness of 100 angstroms is formed thereon, and a contact hole 306 for making contact between the output electrode 108 and a pixel electrode 304 to be described later is formed.

Next, a 6000 angstrom aluminum film is deposited on this by sputtering and patterned to form a pixel electrode 304.

A glass substrate 30 further provided with a transparent counter electrode 105
5 sandwiching the TN liquid crystal 103, the liquid crystal light valve of this embodiment is fully utilized.

Note that an organic insulating material such as silicon oxide or polyimide can also be used for the insulating films 302 and 303.

When using the liquid crystal light valve configured as described above, the writing light 106 is emitted from the glass substrate 301 side, and the reading light 107 is emitted from the glass substrate 305 side.

FIG. 1 shows an equivalent circuit in the form of a two-dimensional array of the liquid crystal light valve of this embodiment.

The photoconductor 101 and the resistor 102 having no photosensitivity constitute a voltage dividing circuit. Output electrode 108 is the output electrode of this voltage divider circuit. Liquid crystal 103 forms a capacitance between output electrode 10B and counter electrode 105.

The operation of this embodiment will be explained with reference to this equivalent circuit.

The electrode 104 is supplied with an AC power supply 109 with an amplitude of ±V,
An AC voltage with an optimal frequency is applied to the TN liquid crystal used. Further, the counter electrode 105 is maintained at O level. The photoconductor 101 and the resistor 102 are designed to have the same shape as described above, and therefore their resistance values in the dark state are approximately equal.

First, when the photoconductor 101 is not irradiated with the writing light 106, the photoconductor 101 and the resistor 1 which does not have photosensitivity
Since the resistance value is almost the same as that of 02, ±V is always divided into voltages of 1-:1, and the potential of the output electrode 108 is always at O level. Therefore, no voltage is applied to the liquid crystal 103.

Conversely, when the writing light 106 is irradiated, the photoconductor 10
1 has a much smaller resistance value than the resistor 102 which has no photosensitivity, and as a result, the potential of the output electrode 108 is
The AC voltage applied to 04 appears almost as is. Therefore, an AC voltage is applied to the liquid crystal 103.

As mentioned above, by turning ON/OFF the photoconductor 101,
The voltage applied to the liquid crystal 103 can be turned ON/OFF, and as a result, the readout light 107 can be modulated by the normal TN effect. [Effects of the Invention] The long manufacturing process, which is a problem with the conventional technology, can be shortened to a fraction of that by using the present invention. This is because the thin film that is each component of the liquid crystal light valve of the present invention is approximately 3000 angstroms thick, and because the absolute film thickness is thin, the time required to form this multilayer film is extremely short. .

On the other hand, the contrast problem is greatly improved by the present invention. This is because the conventional type uses a capacitive voltage divider circuit, so that the voltage change applied to the liquid crystal is small, but in the present invention, the voltage change can be made as large as the withstand voltage of the voltage divider circuit allows. As an actual example, the contrast of the conventional type was less than 1O, but the liquid crystal light valve of the present invention could easily achieve a maximum contrast of 20 to 30.

As explained above, according to the present invention, it is possible to obtain a liquid crystal light valve that is easy to manufacture and has high contrast, and is very useful industrially.

[Brief explanation of drawings]

FIG. 1 is an equivalent circuit diagram of a two-dimensional array of liquid crystal ride valves according to the present invention. FIGS. 2 and 3 are a plan view and a sectional view showing an embodiment of the present invention. FIG. 4 is a conventional This is a diagram showing a liquid crystal light valve. 101...Photoconductor 102...Resistance 103...104...105...106...107...108...109...20!・ ・ ・ 301, 305 ・ 302, 303 ・ 304 ・ ・ ・ 306 ・ ・ 307 ・ ・ 401, 402・Liquid crystal electrode Counter electrode Writing light Reading light output electrode AC power supply Light shielding film Glass substrate Insulating film Pixel electrode Contact hole N-type non-quality silicon transparent conductive film Photoconductive film Light absorption film Multilayer reflective film Spacer Liquid crystal equivalent capacity Multilayer reflective film Equivalent capacitance, Equivalent resistance of light-absorbing film, Equivalent capacitance of light-absorbing film, Equivalent resistance of photoconductive film, Equivalent capacitance of photoconductive film

Claims (1)

[Claims] (1) A liquid crystal light valve in which a one-dimensional or two-dimensional array-like liquid crystal drive circuit that performs switching operations using light is formed on a transparent insulating substrate, and the liquid crystal is sandwiched between an opposing glass substrate with transparent electrodes. A liquid crystal light valve characterized in that the liquid crystal driving circuit is constituted by a voltage dividing circuit including a photoconductor and a resistor having the same shape as the photoconductor and having no photosensitivity.