JPH0815718A - Optical writing type liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide an optical writing type liquid crystal display device capable of forming uniform and high-contrast images without generating the uneven threshold to be generated by scattering by the ruggedness of electrode surfaces and increasing of the electric resistance of these electrodes. CONSTITUTION:This optical writing type liquid crystal display device is disposed with a liquid crystal layer 15, the first electrodes 13 arranged on one surface side of the liquid crystal layer 15, second electrodes 13b which are formed of transparent conductive films of <=1000Angstrom in the max. height difference of the ruggedness on the surface and <=200 or <=100Angstrom in the standard deviation of the ruggedness, the second electrodes 13b which are arranged on the other surface side of the liquid crystal layer 15 and a photoconductive layer 11 which is arranged between the other surface side of the liquid crystal layer 15 and the second electrodes 13b and is changed in impedance when the layer is irradiated with light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photo-writing type liquid crystal display device for forming an image by light irradiation used in a projection type image display device for projecting and displaying an image on a screen.

[0002]

2. Description of the Related Art Conventionally, a projection type image display device for projecting and displaying an image on a screen is disclosed in Japanese Patent Laid-Open No. 4-161926. This projection type image display device is shown in FIG.
As shown in FIG. 4, a lens 2 for forming an image by a laser beam 100 on a reflective liquid crystal light valve 1 as an optical writing type liquid crystal display device, and a reflective liquid crystal light for forming an image corresponding to the image by the light beam 100. The bulb 1, the light source 4, the lens 5 that forms an image of the light from the light source 4 on the polarization beam splitter 6, the polarization beam splitter 6 that transmits light of a predetermined polarization direction, and the reflected light that has passed through the polarization beam splitter 6. The projection lens 7 for enlarging and the screen 8 for projecting the image magnified by the projection lens 7 are provided.

A reflection type liquid crystal light valve 1 as an optical writing type liquid crystal display device has, as shown in FIG. 15, transparent electrodes 10a and 10b made of ITO transparent conductive films on two glass substrates 9a and 9b, respectively. Amorphous silicon hydride (a-S) is formed on the transparent electrode 10b.
A photoconductive layer 11 made of i: H) is formed. Amorphous silicon hydride is produced by plasma chemical vapor deposition using silane gas and hydrogen gas as raw materials. TiO as a dielectric mirror 12 on the photoconductive layer 11
A multilayer film of ₂ and SiO ₂ is formed by the sputtering method. A polyimide film is formed as an alignment film 13b on the dielectric mirror 12 by spin coating, and a polyimide film is formed as an alignment film 13a on the transparent electrode 10a by spin coating. Alignment films 13a, 13
The b is subjected to a molecular orientation treatment by rubbing, and the glass substrates 9a and 9b are bonded together via a seal member 14 including a spacer. A hybrid field effect mode reflective liquid crystal light valve 1 is formed by injecting a mixed nematic liquid crystal added with a chiral material as a liquid crystal layer 15 between the glass substrates 9a and 9b and sealing the liquid crystal layer 15.
A voltage is applied between the transparent electrodes 9a and 9b by an AC power supply 16.

Next, the operation of this conventional example will be described.

Light from the light source 4 enters the liquid crystal light valve 1 through the lens 5 and the changing beam splitter 6.
This incident light is reflected by the dielectric mirror 12 provided in the liquid crystal light valve 1, and the reflected light transmitted through a portion of the liquid crystal layer 15 in which the alignment state is changed has its polarization direction changed by the electro-optical effect. Therefore, it can be transmitted through the beam splitter 6. This reflected light is magnified by the projection lens 7, and the image formed on the light valve 3 is projected on the screen 8.

The operation of the liquid crystal light valve 1 will be described in detail.

A laser beam 100 is scanned from the glass substrate 9b side by a laser beam to write an image. When the laser light 100 is incident, the impedance of the photoconductive layer 11 decreases in the light-exposed region, and the voltage applied by the AC power supply 16 is applied to the liquid crystal layer 15.
Further, in the area not exposed to light, the impedance of the photoconductive layer 11 does not decrease and no voltage is applied to the liquid crystal layer 15. An image is formed by changing the impedance of the photoconductive layer 11. As the operation mode of the liquid crystal light valve 1, a twisted nematic mode, a hybrid field effect mode, a guest host mode, a phase transfer mode, or the like is used.

[0008]

As described above, the conventional photo-writing type liquid crystal display device has the transparent electrodes 10a and 10b.
An ITO transparent conductive film is used as the material. The conductivity of ITO is achieved by heating the substrate at the time of film formation to enhance crystallinity and improve the mobility of the donor. As shown in FIG. The surface of the ITO transparent conductive film has many needle-shaped irregularities. The maximum height difference of the irregularities is 1500 Å, and the standard deviation R value of the irregularities is 250 Å. When the photoconductive layer 11 made of amorphous silicon hydride (a-Si: H) is laminated on the ITO transparent conductive film, the unevenness becomes more seriously scattered due to the difference in crystal growth rate of the uneven surface. When the R value at this time is measured, it is 100
It is 0 angstrom. Therefore, even if a photo-writing type liquid crystal display device is produced, only a liquid crystal display device having a remarkably poor display quality can be produced as shown by B in FIG.

Japanese Unexamined Patent Publication (Kokai) No. 5-346586 discloses an ITO film which is flat and has the same conductivity as before. This ITO film has a structure in which indium oxide InOx and tin oxide SnOx are alternately laminated, and the conductivity is changed by changing the film thickness ratio of indium oxide InOx and tin oxide SnOx and the oxygen partial pressure during manufacturing. The optimum value with transparency is selected. However, there is no specific description about a large number of needle-shaped irregularities generated on the surface of the ITO transparent conductive film, and the irregularities cannot be eliminated. Amorphous silicon hydride (a
It is well known that when forming -Si: H), it is covered with tin oxide to prevent diffusion of indium from the underlying ITO film.

Confidential Technique Vol. 81 No. 213 "Technical Report of the Institute of Electronics and Communication Engineers" by Fujita et al., 1982 1
On CPM 81-79 to 84, PP1-5 on 19th of May,
In the field of solar cells, surface irregularities and device characteristics of an a-Si: H film on an ITOSnOx film stack are described. However, there is no description of numerical parameters for evaluating the surface state, and the a-Si: H film thickness is one-tenth that used in a liquid crystal light valve, which is not a reference.

In the liquid crystal light valve described in Japanese Patent Laid-Open No. 4-161926, SnOx is formed on the ITO film.
Although it is described only to laminate the
Since the electric resistance is larger than that of the ITO film, and the surface irregularity, electric resistance, transmittance, and the like are greatly changed depending on the film forming conditions, these characteristics need to be optimized.

The present invention has been made in order to solve the above problems, and has a uniform and high contrast without scattering due to unevenness of the electrode surface or unevenness in threshold value caused by increase in electric resistance of the electrode. An object of the present invention is to provide an optical writing type liquid crystal display device capable of forming an image.

[0013]

According to the present invention, the above-mentioned object is to prevent the maximum difference in height between the liquid crystal layer means, the first electrode means arranged on one side of the liquid crystal layer means, and the unevenness of the surface. 100
Less than 0 angstrom and standard deviation of unevenness is 200
Second electrode means formed of a transparent conductive film having a thickness of angstrom or less and arranged on the other surface side of the liquid crystal layer means, and arranged between the other surface side of the liquid crystal layer means and the second electrode means, The optical writing type liquid crystal display device according to claim 1, further comprising: an impedance changing layer means whose impedance changes by being irradiated.

The second electrode means has a standard deviation of unevenness of 10
It is preferably formed by a transparent conductive film having a thickness of 0 angstrom or less.

It is preferable that each of the first electrode means and the second electrode means is formed of a transparent conductive film having a surface resistance value of 1 KΩ / □ or less, preferably 100 Ω / □ or less.

It is preferable that each of the first electrode means and the second electrode means includes a tin oxide film layer, and the impedance change layer means includes an amorphous silicon material.

[0017]

In the photo-writing type liquid crystal display device according to claim 1, the maximum height difference of the surface irregularities of the second electrode means is 1000.
Since it is less than angstrom and the standard deviation of unevenness is less than 200 angstrom, scattering due to unevenness does not occur. Furthermore, the cell thickness unevenness of the liquid crystal layer means does not occur, and the orientation of the liquid crystal molecules near the thin film interface becomes good. As a result, the reflectance is improved and a bright, high-contrast display can be obtained.

In the photo-writing type liquid crystal display device according to the second aspect, if the unevenness (standard deviation) of the electrodes becomes small, a-
Abnormal film formation of Si: H can be made less likely to occur, and the reflectance becomes higher when the photowriting liquid crystal display device is used.

In the photo-writing type liquid crystal display device of the third aspect, since the surface electric resistances of the first electrode means and the second electrode means are 1 KΩ / □ or less, the threshold unevenness does not occur and is uniform. Display is obtained.

In the photo-writing type liquid crystal display device according to the fourth aspect, if the surface resistance of the electrode film is small, the voltage loss of the electrode is small even in a large area. Therefore, the photo-writing type liquid crystal display device can be applied to a large area.

In the photo-writing type liquid crystal display device according to the fifth aspect, since the first electrode means and the second electrode means each include a tin oxide film layer, the surface unevenness is often small and bright. Since a high-contrast display can be obtained and the impedance change layer contains an amorphous silicon-based material such as a-Si: H or amorphous silicon hydronitride (a-SiN: H), the electrode means is oxidized. When tin is contained, surface irregularities are often small, unevenness in crystal growth is small, and scattering does not occur. The cell thickness unevenness of the liquid crystal layer means does not occur, and the alignment of the liquid crystal molecules near the thin film interface becomes good. Therefore, the reflectance is improved, and a bright and high-contrast display can be obtained.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the photo-writing type liquid crystal display device of the present invention will be described below with reference to FIG.

The reflection type liquid crystal light valve 1 as the photo-writing type liquid crystal display device is transparent as the first electrode means and the second electrode means made of ITO transparent conductive films on the two glass substrates 9a and 9b, respectively. Electrodes 10a and 10b are respectively formed, and a conductive layer 11 made of amorphous silicon hydride (a-Si: H) as an impedance changing layer means is formed on the transparent electrode 10b via a tin oxide film 10 '. Has been done. Amorphous silicon hydride is produced by plasma chemical vapor deposition using silane gas and hydrogen gas as raw materials. A multilayer film of TiO ₂ and SiO ₂ as a dielectric mirror 12 is formed on the photoconductive layer 11 by a sputtering method. A polyimide film is formed as an alignment film 13b on the dielectric mirror 12 by spin coating, and a polyimide film is formed as an alignment film 13a on the transparent electrode 10a by spin coating. The alignment films 13a and 13b are subjected to a molecular alignment treatment by rubbing, and the glass substrates 9a and 9b are bonded together via a seal member 14 including a spacer. Glass substrate 9
A hybrid nematic liquid crystal light valve 1 of a hybrid field effect mode is formed by injecting and sealing a mixed nematic liquid crystal added with a chiral material as a liquid crystal layer 15 as liquid crystal layer means between a and 9b. Transparent electrode 9
A voltage is applied by the AC power supply 16 between a and 9b.

Next, a method of manufacturing the reflective liquid crystal light valve 1 will be described.

ITO is formed on each of the glass substrates 9a and 9b.
A transparent conductive film is formed with a film thickness of 1000 angstrom. On the ITO transparent conductive film, tin oxide having a film thickness of 200 Å is laminated by the reactive sputtering method to form the transparent electrodes 10a and 10b. The conditions at this time are as follows: tin oxide containing antimony as the target, 50 SCCM of argon supply, 2 SCCM of oxygen partial pressure, 1.2 K of RF output.
W, substrate temperature 300 ° C. When the surface of the transparent electrode is observed with an atomic force microscope, the unevenness becomes smaller than that in the conventional example as shown in FIG. The measurement conditions are a horizontal resolution of 100 Å, a measurement area of 5 μm square, and measurement points of 262144 points. The maximum height difference of the unevenness obtained from this is 1000 Å, the standard deviation of the unevenness is R, the number of measurement points is N, and the height difference of the unevenness at the measurement points is Z.
Letting i be the average value of the height difference of the concavities and convexities, R = {(ΣZ i −Z a) ² / N} ^1/2 standard deviation R is calculated from the following equation to be 200 Å.

A photoconductive layer 11 made of amorphous silicon hydride (a-Si: H) is formed on the transparent electrode 10b. Note that the amorphous silicon hydride is formed by a plasma chemical vapor deposition method using silane gas and hydrogen gas as raw materials. When the surface state at this time was observed with an atomic force microscope, the standard deviation R value was 10 Å. Upon visual observation, specular reflection peculiar to a-Si: H was exhibited, and no scattering state was observed. A multi-layer film of silicon and silicon oxide is formed as a dielectric mirror 12 on the photoconductive layer 11 by a sputtering method. A polyimide film is formed on the transparent electrode as an alignment film 13a by spin coating, and the alignment film 1 is formed on the dielectric mirror 12.
A polyimide film 3b is formed by spin coating, and then the alignment films 13a and 13b are subjected to a molecular alignment treatment by rubbing, and the glass substrates 9a and 9b are bonded together via a seal member 14 including a spacer. A mixed nematic liquid crystal added with a chiral material is injected and sealed as a liquid crystal layer 15 between the glass substrates 9a and 9b.

As a result of measuring the electro-optical characteristics at the time of light irradiation and at the time of darkness, as shown in FIG. 3A, the reflectance at the time of light irradiation is higher than that in the conventional example of FIG. 3B. It can be seen that the rising steepness is also improved. It was confirmed that even if the measurement points were changed in the same picture element and the electro-optical characteristics were measured, the same result was obtained and there was no display unevenness. Electrode 1 at this time
The surface resistance values of 0a and 10b were 45Ω / □.

Next, a second embodiment will be described.

The present applicant investigated the surface irregularity state and the electric resistance value when the oxygen partial pressure during the production of tin oxide and the substrate temperature were changed. As shown in FIGS. 4a and 4b, when the substrate temperature is 300 ° C. and the oxygen partial pressure is 2 SCCM, the maximum height difference of the surface irregularities is 100 angstroms, the standard deviation R value is 20 angstroms, and the electric resistance value is the minimum at 530 Ωcm. . The transmittance of tin oxide prepared under these conditions is 90% on average.
And was good. Next, a third embodiment will be described.

The change in electric resistance value when oxygen gas and nitrogen gas were used during the production of tin oxide was examined. As shown in FIG. 5, when the oxygen partial pressure is 2 SCCM, the electrical resistance is stable at 800Ω / □, which is almost unchanged even when nitrogen is doped. The surface irregularities and the light transmittance were also the same as in the second embodiment. Further, even if this tin oxide film was formed on the ITO film, the same results as in the first embodiment were obtained.

Next, a fourth embodiment will be described with reference to FIG. It should be noted that the same components as those in FIG.

On the glass substrates 9a and 9b, tin oxide having a film thickness of 1400 angstrom was formed under the same conditions as in the first embodiment. Standard deviation R value is 20 Å,
The electric resistance value was 1 KΩ / □. A liquid crystal light valve was prepared in the same manner as described below, and electro-optical characteristics were measured at two locations in the same picture element. As for the result in the dark, as shown in FIG. 7, the movements of the instep point and the second point were exactly the same.

Next, a fifth embodiment will be described with reference to FIG. It should be noted that the same components as those in FIG.

On the glass substrates 9a and 9b, tin oxide having a film thickness of 800 angstrom is formed under the same conditions as in the first embodiment. The standard deviation R value was 20 Å, and the electric resistance value was 4 KΩ / □. A liquid crystal light valve was prepared in the same manner as described below, and electro-optical characteristics were measured at two locations in the same picture element. As a result of darkness, as shown in FIG. 9, the movement of the second point is shifted to a higher potential side than the upper point, and display unevenness occurs.

[0035] From the above results, optical writing type liquid crystal display device
The maximum difference in height of the surface irregularities of the transparent electrodes 10a and 10b is 1
It is preferably 000 angstroms or less. Standard deviation R value
Is less than 200 Å, process variation
100 angstroms or less is better considering
desirable. Also, the electrical resistance is less than 1KΩ / □, process
Considering the margin of variation of 100Ω / □ or less
Is more desirable, and more preferably 10Ω / □
Yes.

Next, a sixth embodiment will be described.

As the photoconductive layer 11 of the first embodiment described above, amorphous hydrogenated silicon nitride (a-SiN: H) is used in place of amorphous hydrogenated silicon (a-Si: H) as disilane gas, Plasma C using hydrogen gas and ammonia gas as raw materials
It was formed on the ITO / tin oxide laminated film by the DV method. The film thickness was about 5 μm, which showed a specific mirror reflection. The liquid crystal light valve 1 was prepared by the same method and the electro-optical characteristics were measured. As a result, the liquid crystal orientation was good, there was no threshold unevenness, and a uniform, bright and high-contrast display was obtained.

Next, a seventh embodiment will be described.

As the photoconductive layer 11 of the above-mentioned fourth embodiment, amorphous hydrogenated silicon nitride (a-SiN: H) is used instead of amorphous hydrogenated silicon (a-Si: H) as disilane gas, Plasma C using hydrogen gas and ammonia gas as raw materials
It was formed on the ITO / tin oxide laminated film by the DV method. The film thickness was about 5 μm, which showed a specific mirror reflection. The liquid crystal light valve 1 was prepared by the same method and the electro-optical characteristics were measured. As a result, the liquid crystal orientation was good, there was no threshold unevenness, and a uniform, bright and high-contrast display was obtained.

The present applicant measured the reflectance by changing the detection angle α of various uneven substrates as shown in FIG.
As shown in FIG. 11, when the detection angle α at which the reflectance was 50% was 10 degrees or more, the scattering reduction was visually confirmed.
Therefore, light is applied to the surface of the conventional example, the first example, and the fourth example of the amorphous silicon hydride (a-Si: H), and the detection angle β at which the reflectance is 50% is investigated. It was When the detection angle β is 10 degrees, the reflectance is 50%, and as shown in FIG. 12, the standard deviation R value of the surface irregularities of the electrode when the detection angle β is 10 degrees is about 220 angstroms, which is shown in FIG. As described above, the standard deviation R of the first embodiment and the fourth embodiment is
Since the values are 200 angstroms and 20 angstroms, scattering does not occur, and the contrast and brightness are improved as compared with the conventional example.

[0041]

According to the photo-writing type liquid crystal display device of the present invention, since the maximum height difference of the unevenness of the electrode surface is 1000 angstroms or less and the standard deviation of the unevenness is 200 angstroms or less, scattering occurs. In addition, since the cell thickness of the liquid crystal layer is not uneven, the alignment of liquid crystal molecules near the thin film interface is also good. As a result, the reflectance is improved and a bright, high-contrast display can be obtained.

In the photo-writing type liquid crystal display device according to the second aspect, if the unevenness (standard deviation) of the electrodes becomes small, a-
Abnormal film formation of Si: H can be made less likely to occur, and the reflectance becomes higher when the photowriting liquid crystal display device is used.

According to the optical writing type liquid crystal display device of the third aspect, since the surface resistance value of the electrode is 1 KΩ / □ or less, the threshold unevenness does not occur and a uniform display can be obtained.

In the photo-writing liquid crystal display device according to the fourth aspect, if the surface resistance of the electrode film is small, the voltage loss of the electrode is small even in a large area, so that the photo-writing liquid crystal display device can be applied to a large area.

According to the optical writing type liquid crystal display device of the fifth aspect, since the electrodes include the tin oxide film layer, the surface unevenness is reduced, and a brighter and higher contrast display can be obtained. Since the conductive layer contains an amorphous silicon-based material, when tin oxide is contained in the base material, surface irregularities are often small, so unevenness in crystal growth is small and scattering does not occur. . The unevenness of the cell thickness of the liquid crystal layer does not occur, and the alignment of liquid crystal molecules near the thin film interface becomes good. As a result, the reflectance is improved and a bright, high-contrast display can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a photo-writing type liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing an AMF observation result of the optically writable liquid crystal display device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing electro-optical characteristics of the optical writing type liquid crystal display device according to the first example of the present invention.

FIG. 4a is a diagram showing changes in electric resistance value when oxygen partial pressure is changed in the second embodiment of the present invention.

FIG. 4b is a diagram showing changes in the standard deviation value when the oxygen partial pressure is changed in the second embodiment of the present invention.

FIG. 5 is a diagram showing a change in electric resistance value when a nitrogen partial pressure is changed in the third embodiment of the present invention.

FIG. 6 is a sectional view showing a photo-writing type liquid crystal display device of a fourth embodiment of the present invention. It is a figure which shows the viewing angle dependence of the contrast ratio of a liquid crystal display panel.

FIG. 7 is a diagram showing electro-optical characteristics of a photo-writing type liquid crystal display device according to a fourth example of the present invention.

FIG. 8 is a sectional view showing a photo-writing type liquid crystal display device according to a fifth embodiment of the present invention.

FIG. 9 is a diagram showing electro-optical characteristics of a photo-writing type liquid crystal display device according to a fifth example of the present invention.

FIG. 10 is a diagram showing an experimental method performed by the applicant.

FIG. 11 is a diagram showing the result of an experiment conducted by the applicant.

FIG. 12 is a diagram showing the result of an experiment conducted by the applicant.

FIG. 13 is a diagram showing the result of an experiment conducted by the applicant.

FIG. 14 is a diagram showing a schematic configuration of a conventional projection-type image display device.

FIG. 15 is a cross-sectional view showing a conventional photo-writing type liquid crystal display device.

FIG. 16 is a perspective view showing an AMF observation result of a conventional photo-writing type liquid crystal display device.

[Explanation of symbols] 1 Optical writing type liquid crystal display device 9a, 9b Glass substrate 10a, 10b Electrode 11 Photoconductive layer 12 Dielectric mirror 13a, 13b Alignment film 15 Liquid crystal layer 16 Power supply

Claims (5)

[Claims] 1. A transparent liquid crystal layer means, a first electrode means arranged on one surface side of the liquid crystal layer means, and a maximum unevenness of surface irregularities of 1000 angstroms or less and a standard deviation of the irregularities of 200 angstroms or less. Second electrode means formed of a conductive film and arranged on the other surface side of the liquid crystal layer means, and arranged between the other surface side of the liquid crystal layer means and the second electrode means and irradiated with light. An optical writing type liquid crystal display device comprising: an impedance changing layer means whose impedance changes by 2. The second electrode means has a standard deviation of unevenness of 1
The photo-writing type liquid crystal device according to claim 1, wherein the photo-writing type liquid crystal device is formed of a transparent conductive film having a thickness of 00 Å or less. 3. The photo-writing liquid crystal according to claim 1, wherein each of the first electrode means and the second electrode means is formed of a transparent conductive film having a surface resistance value of 1 KΩ / □ or less. Display device. 4. The photo-writing liquid crystal display device according to claim 3, wherein each of the first electrode means and the second electrode means is formed of a transparent conductive film having a surface resistance value of 100 Ω / □ or less. . 5. The method according to claim 1, wherein each of the first electrode means and the second electrode means includes a tin oxide film layer, and the impedance change layer includes an amorphous silicon material. The optical writing type liquid crystal display device described.