JPH0328826A - Spatial modulating element - Google Patents

Abstract

PURPOSE:To enable threshold processing for multi-input by providing a liquid crystal tank, a part which has photoconductivity, and field-effect transistors(TFT), irradiating the photoconductive part with light, and modulating the intensity of an electric field applied to the liquid crystal tank. CONSTITUTION:This element consists of the TFTs 1 and 2, liquid crystal tank(CLC), and photoconductive tank(CPC). Then when the TFT1 is applied with VG at its gate electrode and then turns on to charge the CPC, the VG is reduced to turn off the TFT1, the gate voltage of the TFT2 is nearly equal to VF, and the TFT2 conducts to apply an AC voltage V to the CLC. Then the CPC is irradiated with light and when the light intensity becomes large enough to reduce the resistivity sufficiently, charges accumulated in the CPC are neutralized and the gate voltage of the TFT2 drops. Consequently, the TFT2 turns off and the AC voltage V is not applied to the CLC and more. Consequently, the voltage applied to the CLC can be controlled by the light irradiation and the threshold processing for multi-input is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a spatial light modulation element used in optical arithmetic devices and projection displays.

2. Description of the Related Art Among conventional spatial light modulators using liquid crystals, there is one that has a threshold processing function.As shown in FIG. A spatial light modulation element 905 has been proposed in which these are sandwiched between ITO transparent electrodes 903 and 904 (Kuniharu Takizawa et al.
5th Japan Society of Applied Physics Related Conference Lecture Preliminary Lecture Collection Spring 1986 30p-ZF-3, 309-ZF-4>.

In addition, as an optical logic operation element using a liquid crystal, as shown in the equivalent circuit of FIG. A structure in which connected TFTs 1004 are connected has been proposed (Hiroshi Hamano et al., 14th Liquid Crystal Symposium, 1000 Lectures, September 1988, 2D304).

Problems to be Solved by the Invention Conventional spatial light modulator 905LL. shown in FIG.
The liquid crystal layer 902 and the photoconductive layer 901 are connected to electrodes 903 and 904.
Even if the structure is sandwiched between the photoconductive layer 901 and the photoconductive layer 901, this structure (in order to prevent too much voltage from being applied to the liquid crystal layer 902 when blocking light)
It may be necessary to make it lower than that of 02, but the liquid crystal layer 90
Since the dielectric constant of 2 is small, the film thickness of the photoconductive layer 901 is 2a.
Therefore, there is a problem that the transmitted light intensity becomes small and a large incident light intensity is required.Also, this element has a threshold function; The power support has the characteristic of being controllable by changing the voltage and frequency.Although it has the problem of not being able to perform threshold processing for multiple human forces. Since the device does not have a laminated structure of a liquid crystal layer and a photoconductive layer, a large incident light intensity is not required to operate the device. However, when operating as a threshold device, the threshold value cannot be controlled. Moreover, it has the problem of not being able to perform threshold processing against multiple human resources.

The present invention aims to solve the problems of the prior art.

Means for Solving the Problems Spatial light modulator of the present invention Table 1 Comprising a liquid crystal layer, a photoconductive part, and a field effect transistor L A field effect transistor driving the liquid crystal layer has photoconductivity The liquid crystal layer is characterized in that the electric field strength applied to the liquid crystal layer is modulated by irradiating light to the part having photoconductivity and to which the part having photoconductivity is electrically connected. A structure is adopted in which a photoconductive part (hereinafter abbreviated as PC part) is electrically connected to the TPT driving the LPG (for example, the PC part is connected to the gate electrode). If the part is not irradiated with light, it holds a capacitance and acts as a capacitor. If it is irradiated with light, it loses its function and the charged charge disappears. Therefore, the charged PC part is connected to the gate electrode. If the TPT is in a conductive state in this state, the conduction state of the TPT can be cut off by irradiating the PC part with light.At this time, the capacitance of the PC part is the same as the capacitance of the TPT gate. However, even if the film thickness of the PC part is made thinner, the area of the PC part can be reduced. In addition, since the film thickness of the PC part is thin, the electric field in the PC part is large, and even if the incident light is weak, optically excited carriers can be transported throughout the PC part, increasing the degree of freedom in selecting a light source and reducing light source consumption. Although the power can be reduced, if multiple PC parts are connected in series and these PC parts are charged with the gate voltage, the gate voltage will change depending on the number of PC parts that are irradiated with light, and the operating state of the TPT will change. In other words, by using this series connection structure, it is possible to perform threshold processing for multiple inputs.
The capacitance of the PC part can be reduced overall, and
The threshold value can be set arbitrarily by irradiating a predetermined PC part with light before threshold processing or by changing the gate voltage. This will be explained with reference to the drawings.

Embodiments of the present invention will be described with reference to the drawings. Embodiment 1 FIG. 1 shows an equivalent circuit diagram of an embodiment of the spatial light modulation element of the present invention. This spatial modulation element basically consists of two TFTs (
TFTI, TFT2) and liquid crystal layer (CLc as capacitance)
) and t4 from the photoconductive layer The photoconductive layer is connected between the gate electrode of TFT2 and the ground, and acts as a dielectric when no light is irradiated, so it is expressed as capacitance CPC.

The operation of the spatial light modulator will be explained using this circuit diagram. 4 Vo is applied to the gate electrode of TFTI h T
FTI becomes conductive and the photoconductive layer Cpc is charged 7). Cp
When charging of c is completed, Vo is decreased to cut off conduction of TFT1. At this time, the gate voltage of TFT2 is approximately Vp
, TPT2 is conductive and the AC voltage V is applied to the liquid crystal layer CLC.
is applied, and then the photoconductive layer CPc is irradiated with light, and when the light intensity becomes large enough to sufficiently reduce the resistivity of the photoconductive layer, the charges stored in the photoconductive layer are neutralized L T
Although the gate voltage of FT2 decreases, the conduction of △ TFT2 is cut off, and the alternating current voltage V is no longer applied to the liquid crystal layer CLC.

In this manner, the voltage applied to the liquid crystal layer can be controlled by light irradiation, and the device can be operated as a spatial light modulator having a threshold processing function.

An example of the spatial light modulation element of this equivalent circuit will be explained using the schematic cross-sectional view shown in FIG. The semiconductor layer 201 is formed on one of the glass substrates 202 using TPT. First, the gate electrode 203 is formed on the glass substrate 202 by forming the gate electrode 203 on the glass substrate 202.
After that, the gate insulating film 204 and the semiconductor layer 20
11 Shape the semiconductor protective layer 205 by plasma CVD method.
After patterning and interposing an n-type semiconductor layer 206 to improve ohmic properties, the source electrode 206
7. Connect the drain electrode 208 all at once with A1, etc.
,, TPT is fabricated, and then a transparent electrode 209 is formed using, for example, I
It is connected to the gate electrode 203 through a hole formed with TO or etched in the gate insulating film 204. For example, a-Si:f{ is formed or patterned as a photoconductive layer 210 thereon, and a transparent electrode 211 is formed on the photoconductive layer 21.
Next, a pixel electrode 213 for applying an electric field to the liquid crystal 2+2 was formed using a transparent electrode such as IT○.Then, an alignment film 214 was applied and a rubbing process was applied to the other glass substrate 215. A counter electrode 216 and a light shielding layer 217 are provided, and an alignment film 218 is similarly applied and rubbed.
TPT semiconductor layer 2011 with a twisted nematic liquid crystal 212 sealed between both substrates and polarizing plates 219 arranged before and after the substrates is not only a-Si:H, but also a-Si:H.
Polycrystalline silicon, single crystalline silicon or polycrystalline GaAa
, single crystal GaAs, a-Si+ -wing Cx :H,
a-Si+ -xGex :}l (0<x<1), etc. (Also, the photoconductive layer 210 is
i: CdS instead of H, CdT6 CdSe,
ZnS, ZnSe, GaAs, GaN, GaP
, jaAIAs, InP and other compound semiconductors
Non-quality semiconductors such as e, SeTe, AsSe,
Si, Ge, SL+-xcx, Sx+-*Ge
x, Ge+-xcw (0<X<1); and (l) phthalocyanine pigment (
(abbreviated as Pc), for example, metal-free Pc, XPc (X
=Cu, Ni, Co, TiO, MzSi(
OR)t etc.), AICIPcCl, TiOCIP
cCl, InCIPcCLInCIPc, In
BrPcBr, etc. (2) Monoazo dyes, azo dyes such as disazo dyes (3) Benylene dyes such as penylene acid anhydride and penylene acid imide (4) Indigoid dyes, (5) Quinacridone dyes (6) Anthraquinones Sales Polycyclic beef non-short forms such as pyrenequinones (7)
Cyanine colored fish (8) Xanthene dye, (9) PVK/
Charge transfer complexes such as TNF (IO) and eutectic complexes formed from biryllium salt dyes and polycarbonate resins.
11) Desired characteristics can also be obtained by using an organic semiconductor such as an azulenium salt compound.
10 a-Si:H, a-Si+ -w Gex:H
, a-Sit-XCX :Hla-Ge :H
, a-Get-XCX: H or polycrystalline Sl,
Ge, Sit-xCx, SL+-xGfl. +, Get
When using -xCx, it may contain halogens such as fluorine, chlorine, and bromine, and it may also contain oxygen or nitrogen to increase dark resistivity.Also, it may contain B as a p-type impurity to control resistivity. , Al, Ga, or n-type impurities such as P, As,
It is also possible to add elements such as sb. By stacking semiconductor materials doped with impurities in this way, p/n, p/l, i/
The photoconductive layer 2 is formed by forming junctions such as n, p/i/n, etc.
It is also possible to control the dielectric constant and resistivity (t).Also, it is also possible to use a single layer of photoconductive materials such as those mentioned above (t).A heterojunction in which two or more types of photoconductive materials are laminated can be formed. Alternatively, the dielectric constant and resistivity of the photoconductive layer 210 may be controlled by 1.%.
FIG. 3(a) shows the change in transmitted light intensity with respect to the incident light intensity irradiated from the T-shaped glass substrate 202 side. My name is L. It is assumed that the polarization directions of the two polarizing plates 219 are perpendicular to each other. When the intensity of the incident light exceeds a certain value, a threshold characteristic can be observed that allows a large amount of transmitted light to be obtained.
b) Lt, a- of the photoconductive layer 210 as the incident light intensity;
It shows the change in the transmitted light intensity with respect to the incident light intensity when focusing on light with a transmitted light intensity of 650nII1 or more for light of 650 nm or less, which Si+H absorbs well. However, in this case, in the direction perpendicular to the polarization direction. i;L
By using a color polarizing plate as the polarizing plate 219, which hardly transmits light with wavelengths shorter than 650 nm but sufficiently transmits light with long wavelengths, 1, it is possible to obtain a threshold characteristic in which the intensity of transmitted light is saturated at a place where the intensity of incident light is large. Figure 3 (a)
．． (b) In either case, the incident light intensity that provides the threshold value is on the order of several μW/c, which can be reduced by more than three orders of magnitude compared to the conventional example shown in FIG. FIG. 4 shows an equivalent circuit of an example of a spatial light modulation element in which a photoconductive layer is connected to the source electrode of the liquid crystal layer and a photoconductive layer is connected in series.

The operating characteristics of this circuit will be explained. When voltage VLI is applied to the gate electrode of L TFTl, the TFTI becomes conductive, and the photoconductive layer (the capacitance when no light is irradiated is Cpc) and the liquid crystal layer (capacitance However, since CPc is as small as or smaller than CLC, the AC voltage V is mainly applied to the photoconductive layer CPc, and too little is applied to the liquid crystal layer CLC. Karana (1) Next, when the photoconductive layer CPC is irradiated with light and the resistivity of the photoconductive layer is made sufficiently small, an AC voltage V is applied to the CLC. Therefore, the voltage applied to the liquid crystal layer is changed by light irradiation. However, an example of the spatial light modulator of this equivalent circuit will be explained using the schematic cross-sectional view shown in FIG. membrane 5
02. , gate electrode 503. semiconductor protective layer 504,
Using the same materials as in the case of FIG. The source electrode 506 and the drain electrode 507 are formed in one package. After forming the transparent electrode 510 with ITO or the like, the photoconductive material described in Example 1 is laminated.
After patterning 1, a resistive electrode 511 is formed, an alignment film 512 is applied, and a rubbing process is performed.On the other glass substrate 513, a counter electrode 514 and a light shielding layer 5 are formed.
15, and apply the alignment film 516 in the same way.Rubbing treatment is performed, but this rubbing treatment is performed in a direction shifted by about 90" from the previous substrate.Twisted nematic liquid crystal 5 is placed between both substrates.
FIG. 6(a) shows the change in transmitted light intensity with respect to the incident light intensity of this spatial light modulation element. At this time, when the polarization directions of the polarizing plates 518 are parallel to each other, the intensity of the incident light increases, and when the resistivity of the photoconductive layer 509 decreases sufficiently, the intensity of the transmitted light increases, and the threshold characteristic cannot be exhibited. Similarly to the case of FIG. 6(b) GA, FIG. 3(b), the transmittance in the direction perpendicular to the polarization direction is good on the long wavelength side, with the wavelength (λ1) at which the photoconductive layer 509 absorbs well. Polarizing plate 51 is a color polarizing plate that transmits light but hardly transmits light on the short wavelength side.
Even in the operating characteristics when used in the TPT gate voltage and the incident light In addition, if the polarization directions of the polarizing plates 518 are orthogonal to each other, it may work as an AND element. In Examples 1 and 2, an example of a transmissive spatial light modulator will be described. As shown in Example 3 below, a reflective layer and an absorbing layer may be provided to create a reflective structure (Example 3) As shown in FIG. The operation of the circuit is basically the same as in the case shown in Fig. 1, and a large number of photoconductive layers (CPCI, CPCP, -, CPcn
) is connected in series to the gate electrode of TPT2.
By irradiating these photoconductive layers with light, TFT2
In this case, the voltage applied to the liquid crystal layer changes depending on the number of photoconductive layers irradiated with light. ) A cross-sectional view of an example of a spatial light modulation element represented by this equivalent circuit and a plan view of the element structure on one glass substrate 80 are shown, respectively.

However, the number n of photoconductive layers was set to 4. Glass substrate 80
1 on 2 TFTs (TFT 1802.TFT280
3) and four photoconductive layers 804 e.g. a-Sit-xcx
This spatial light modulation element has a reflective configuration, and is TFTI, 2802.80
A light absorption layer 806 and a light reflection layer 807 are laminated on the transparent electrode 805 and the readout light 808 is TFTI,
2802.803 and the photoconductive layer 804, and the incident light 809 from leaking to the liquid crystal layer 810.However, in the plan view of FIG. 8(b), C.
A pixel electrode 811 for applying an electric field to the liquid crystal 810 and a connection electrode 812 for connecting the photoconductive layer 804 in series.
In order to make it easier to understand, the light reflecting layer 807 and the light absorbing layer 806 are omitted.The liquid crystal molecules are twisted by about 45 degrees, and the polarization directions of the polarizer 813 and the analyzer 814 are orthogonal to each other. Apply AC voltage V to the modulation element and set the wavelength to 350
The operating characteristics were investigated by changing the number of photoconductive layers 804 irradiated with incident light of ~600 nm and using a He-Ne laser as the readout light 808, and the results are shown in Figure 8 (
As shown in c), output light 815 is obtained by irradiating a predetermined number of photoconductive layers 804 or more with incident light 808, and the threshold characteristic has been confirmed. When Vp is increased,
It was also recognized that the number of photoconductive layers from which output light 815 can be obtained increases.Also, when the photoconductive layer is connected in series with the liquid crystal layer as shown in Fig. 4, it is possible to connect multiple photoconductive layers in series. We also investigated the connected spatial light modulator, and found that when the number of photoconductive layers irradiated with light exceeds a certain value, output light is obtained and a threshold characteristic is observed. It was confirmed that by increasing the value of voltage V, the number of photoconductive layers that are irradiated with light to obtain output light decreases.9 For the above two examples, four or more photoconductive layers are connected in series. A similar phenomenon was observed when k was increased to It has the advantage of being able to control & threshold values when operated as a threshold element, and also capable of threshold processing for multiple inputs.

[Brief explanation of drawings]

FIG. 1 shows an equivalent circuit of an embodiment of the spatial light modulator according to the present invention. FIG. 2 shows a schematic cross-section of the structure of the same embodiment.
Figures (a) and (b) show the operating characteristics of the same embodiment. Figure 4 is an equivalent circuit diagram of another embodiment of the spatial light modulator according to the present invention. Figure 5 shows a schematic cross-section of the structure of the same embodiment. Figure 6 (a)
, (b) shows the operating characteristics of the same embodiment. FIG. 7 shows the equivalent circuit of another embodiment of the spatial light modulation element according to the present invention. FIG. 8 (a) shows the cross section of the structure of the same embodiment. (b) shows its plane; FIG. 8(c) shows the operating characteristics of the same embodiment; FIGS. 9 and 10 show the conventional example. 214...Glass base 203...Gate electric maple 204...Gate insulation J
lu 205... Semiconductor protective clothing 206... N-type semiconductor wire 207... Source electric current K 208... Drain electric current ffi 209,211... Transparent electric current K 2
10...Photoconductive screen 212...Liquid crystal 213...
Pixel electrodes 214, 218... Orienting glass 216... Opposing electric maple 217... Light shielding plate 219... Polarizing plate 5
01...Semiconductor wind 502...Gate insulation wind 503.
...Gate Denho 504...Semiconductor Protection Phoenix 505...
N-type semiconductor #5o6...source charge 507...drain charge! 508,513...Glass Motosaka 509・
...Photoconductor 510. 511...Transparent electric conduction 512
, 526... Directed wind 514... Opposed 'iffi
515...shading benefit 51? ...Liquid crystal 518...Polarized light K 801...Glass base i 802-T F
T 1, 803-T F T 2, 804-...Photoconductive 凰8o5...Transparent electric maple 806...Light-absorbing 凰8
07...Light reflecting 凰 808...Reading i 80
9...Incidence-i 810...Liquid &811...Pixel electric maple 812...Connection electric maple 813...Polarizer,
814...analyzer, 815...output

Claims (4)

[Claims] (1) comprising a liquid crystal layer, a photoconductive portion, and a field effect transistor, the photoconductive portion being electrically connected to the field effect transistor driving the liquid crystal layer; A spatial light modulator, characterized in that the intensity of the electric field applied to the liquid crystal layer is modulated by irradiating the photoconductive portion with light. (2) The spatial light modulator according to claim 1, characterized in that there are a plurality of photoconductive parts, and some parts are connected in series. (3) The spatial light modulator according to claim 1, wherein the photoconductive portion includes a depletion layer. (4) The spatial light modulator according to claim 1, wherein the photoconductive portion includes a heterojunction.