JP2818985B2 - Light valve device and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat light valve device used for a direct-view display device and a projection display device. More specifically, the present invention relates to a light valve device such as an active matrix liquid crystal display device in which an integrated circuit in which a drive circuit is formed on a semiconductor thin film is integrally incorporated as a liquid crystal panel.

[0002]

2. Description of the Related Art The principle of an active matrix liquid crystal display device is extremely simple.
When a specific pixel is selected, the corresponding switch element is turned on, and when not selected, the switch element is turned off. This switch element is formed on a glass substrate constituting a liquid crystal panel. Therefore, the technology for thinning the switch element is important. Usually, a thin film transistor is used as this element.

In a conventional active matrix device, as shown in a schematic sectional view of FIG. 4, a substrate 14 comprises a carrier layer 15 made of, for example, glass, quartz, etc., and an amorphous silicon thin film or a multi-layer formed thereon. A thin film transistor 16 made of a crystalline silicon thin film, a pixel driving electrode 17 connected to the thin film transistor 16, and an alignment film 18 made of an organic film such as polyimide are provided. Have been. A liquid crystal drive electrode 21 and an alignment film 22 are also formed on a surface of the opposing second substrate 20 opposing the substrate 14, and a liquid crystal 23 is held between the substrate 14 and the substrate 20. Further, the polarizing plate 2 is sandwiched between the substrate 14 and the substrate 20.
4 and 25 are arranged. The liquid crystal 19 has an alignment film 18 or 2 at an interface in contact with the substrate 14 or the substrate 20.
By the action of 2, the alignment is performed in the alignment direction defined by the alignment film.

In the case of a normal TN type liquid crystal, the alignment direction at the interface of the substrate 14 and the alignment direction at the interface of the substrate 20 are set to be different by 90 degrees. The first polarizing plate 24 is arranged parallel to the orientation direction of the substrate 14, and the second polarizing plate 25 is arranged parallel to the first polarizing plate 24 or at a position in a polarization direction perpendicular to the first polarizing plate 24. The operation as the light valve device is such that when no voltage is applied to the pixel drive electrode 4, the incident polarized light rotates in the direction of polarization according to the orientation of the liquid crystal 23 and becomes polarized light in a direction twisted by 90 degrees with the incident light. The second polarizer 25 emits light and the first polarizer 24
When the light is parallel, the emitted light is absorbed by the polarizing plate 25. When a sufficiently high voltage is applied between the pixel drive electrodes 21 and 16, the liquid crystal 23 is aligned perpendicular to the alignment film surface. In this case, since the polarization direction of the incident light is not rotated by the liquid crystal, it passes through the polarizing plate 25. Since the spacer 19 is usually formed by spraying, it is difficult to control its position.
The distribution is non-uniform depending on the location, and may be on the liquid crystal drive electrode 17 or on the transistor 16. The spacer on the liquid crystal driving electrode hinders the electro-optic effect. Active matrix liquid crystal display devices having an area of about 3 inches to 10 inches are commercially produced. Since the amorphous silicon thin film can be formed at a low temperature of 350 ° C. or less, it is suitable for a large-area liquid crystal panel. Further, in an active matrix liquid crystal display device using a polycrystalline silicon film, a small liquid crystal display panel of about 2 inches is currently commercially produced.

[0005]

However, a conventional active matrix liquid crystal display device using an amorphous silicon thin film or a polycrystalline silicon thin film is suitable for a direct-view type display device requiring a relatively large screen image surface. On the other hand, it is not necessarily suitable for miniaturization of the device and high density of pixels. Recently, apart from the direct-view display device, there has been an increasing demand for an ultra-small display device or a light valve device having miniaturized high-density pixels. Such a micro light valve device,
For example, it is used as a primary image forming surface of a projection type image device, and can be applied as a projection type high definition television. Several tens of μm by using fine semiconductor manufacturing technology
An ultra-small, high-definition light valve device having a pixel size on the order and a size of about several cm as a whole is possible.

In a conventional method of forming a liquid crystal cell, a thin film of polyimide or the like is applied on a first substrate, and this is rubbed with a cloth or the like to form a liquid crystal alignment film.
A fiber or spherical spacer material having a size of m is scattered, and the second substrate is bonded to the first substrate at a distance determined by the diameter of the spacer material. Here, the spacer material is sprinkled irregularly on the pixel electrode, thereby excluding the liquid crystal in this portion. There is no particular problem when the size of the spacer is smaller than the pixel drive electrode, but when the number of pixels increases with the improvement in the display quality of the light valve device, and when the pixel size decreases, the spacer comes over the pixel drive electrode. The size of the spacer is not negligible compared to the size of the pixel electrode.

In particular, when the pixel size and the thickness of the liquid crystal layer are substantially the same, the pixel electrode is covered by the spacer. Therefore, the electro-optical effect does not work on the pixel driving electrode on the pixel electrode on which the spacer exists, so that the electro-optical characteristics of the light valve device are degraded. For example, in a TN-type liquid crystal display, a portion where black display is to be performed becomes white and the display contrast is reduced, and phenomena such as black dots floating on a white display background occur. For example, if the area where the electro-optic effect does not work occupies 1/100 or more of the pixel driving electrode, a light valve device having a contrast ratio of 100: 1 or more cannot be realized. A method of bonding the first substrate and the second substrate without dispersing the spacers is also conceivable, but it is practical to keep the distance between the two substrates at a few microns and keep it constant considering the unevenness and warpage of the substrates. It is very difficult. After forming the irregularities on the surface of the first substrate, it is also conceivable to form an alignment film on the substrate surface.

In this case, the contrast of the light valve device is not reduced if the position of the unevenness is selectively formed by lithography or the like in a region where the electro-optic effect of the light valve device is not used. However, according to the rubbing orientation generally used, an orientation film cannot be formed in a portion blocked by the convex portion. In the case where an alignment film is formed by oblique deposition of silicon oxide, a shadow several times as high as the height of the alignment film is formed by the projections, and the alignment film cannot be formed uniformly.

SUMMARY OF THE INVENTION An object of the present invention is to provide a light valve device such as an active matrix liquid crystal display device which is ultra-compact and has a fine display quality in order to solve the conventional problems. And In order to achieve this object, in the present invention, the organic spacer layer formed on the inorganic alignment film is formed by lithography.

Further, by controlling the position of the spacer layer, it is easy to keep the distance between the opposing substrates constant. That is, if the spacer distribution is irregular, the distance between the substrates tends to be irregular. It is another object of the present invention to maintain the distance between the substrates accurately. Furthermore, the number of spacers is usually 1
As described above, it is about 00 to 500 pieces / mm ² , and if the number is more than this, the display quality is adversely affected as described above. In the present invention, it is possible to increase the number of spacers to reduce the number of spacers. It is another object of the present invention to reduce stress and to prevent destruction of switch elements on a substrate due to stress.

[0011]

The means adopted by the present invention to solve the above-mentioned problems are as follows. A liquid crystal layer is disposed between the first substrate and the second substrate opposed to each other on which the liquid crystal alignment layer is formed, and at least one of the two pairs of substrates is provided with projections and depressions. In the light valve device in contact with the surface of the other counter substrate at the portion, at least the liquid crystal alignment film of the substrate provided with irregularities is formed of an inorganic material, and the structure of the irregularities is formed of an organic material The method for manufacturing a substrate having the unevenness is characterized in that at least (A) a step of forming an alignment film of an inorganic material on a substrate by a method such as oblique evaporation of silicon monoxide. (B) a step of applying a thin film made of an organic material such as polyimide on the alignment film. (C) a step of selectively removing the thin film layer made of the organic material by lithography or the like while leaving a part thereof.

[0012]

In the light valve device configured as described above,
Since the alignment film in a state capable of aligning the liquid crystal is made of an inorganic material, the processing temperature is low even through a process such as lithography to apply or selectively form an organic material spacer on the alignment film. Does not impair the liquid crystal alignment ability. As a result, the spacer on the pixel drive electrode can be eliminated, and the spacer can be selectively provided in the non-display portion, and the spacer does not deteriorate the electro-optical characteristics of the light valve device.

Further, since the spacers can be regularly arranged, the distance between the substrates can be accurately maintained, so that the uniformity of the in-plane characteristics of the light valve device can be improved. Further, since the number of spacers can be substantially increased, the concentration of stress in the spacer portion can be reduced, and element destruction due to stress can be prevented.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic sectional structure of a light valve device used in the present invention. As shown in the figure, a first substrate 1 includes a carrier layer 2 made of, for example, glass, quartz, or the like, a thin film transistor 3 formed of an active element formed thereon, and a pixel driving electrode 4 connected to the thin film transistor 3. An alignment film 5 made of an inorganic material formed so as to cover the pixel drive electrode 4, and a spacer as a convex portion made of an organic material selectively formed on the alignment film 5 so as not to overlap the pixel drive electrode 4 in a plane. Consists of six. As the thin film transistor, an insulated gate field effect transistor generally including a gate electrode, a gate insulating film, a semiconductor film, a source, a drain electrode, and the like is generally used. First substrate 1 of opposed second substrate 7
A liquid crystal driving electrode 8 and an alignment film 9 are also formed on a surface facing the substrate 1, and a liquid crystal 10 is held between the substrate 1 and the substrate 7. Further, the polarizing plates 11 and 1 are sandwiched between the substrate 1 and the substrate 7.
2 are arranged. The liquid crystal is oriented in the orientation defined by the orientation film by the action of the orientation film 9 or 5 at the interface in contact with the opposing substrate 1 or 2.

In the case of a normal TN type liquid crystal, the alignment direction at the interface of the substrate 1 and the alignment direction at the interface of the substrate 7 are set to be different by 90 degrees. The first polarizing plate 11 is arranged in parallel with the orientation direction of the substrate 1, and the second polarizing plate 12 is arranged in parallel with or perpendicular to the first polarizing plate 11. The operation as the light valve device is such that when no voltage is applied to the pixel drive electrode 4, the incident polarized light rotates in the direction of polarization according to the orientation of the liquid crystal 10, and becomes polarized light in a direction twisted by 90 degrees with the incident light. When the light is emitted and the second polarizing plate 12 is parallel to the first polarizing plate 11, the emitted light is absorbed by the polarizing plate 12. When a sufficiently high voltage is applied to the pixel drive electrode 4, the liquid crystal is aligned perpendicular to the alignment film surface. In this case, since the polarization direction of the incident light is not rotated by the liquid crystal, it passes through the polarizing plate 12. Since the spacer 6 can be selectively formed in a region where the pixel drive electrode 4 is not provided, the light modulation operation of the light valve device is not hindered. As the alignment film 5, for example, it is known that an obliquely deposited silicon monoxide film has good liquid crystal alignment characteristics as an inorganic material film.

It is known that when fine geometrical irregularities are formed on the surface of an insulating film such as a silicon dioxide film at an interval of about 1 micron or less, the film has an orientation characteristic. these,
In order to realize the alignment characteristics of the alignment film, fine geometrical irregularities on the alignment film surface play a major role. As the alignment film applied for forming the spacer, for example, a photosensitive polyimide film can be considered. This film is applied on a substrate by using a spin coating method or the like, and selectively exposed to light with a photomask or the like, so that a spacer corresponding to the thickness of the polyimide film applied at a selected position can be formed. When photosensitive polyimide is used, selective formation is possible without using a photoresist. In the process of forming the spacer using the polyimide film, the temperature during the process is at most 250 ° C. or less, so that the geometrical shape of the surface of the alignment film made of an inorganic material formed thereunder does not change, and the alignment performance does not change. Has no effect.

The present invention can be applied irrespective of the size of the pixel of the light valve device. In particular, when the size of the pixel becomes too small to be ignored compared to the size of the spacer,
Advantageously, it is possible to prevent the spacer from blocking light transmitted through the light valve device. When the spacer is spherical or fiber-shaped, the contact area between the spacer and the substrate is small, so that locally large pressure is generated at the contact portion between the spacer and the substrate. According to the present invention, since the spacer and the substrate are in flat contact, the contact pressure can be greatly reduced. This does not cause breakdown of the thin film transistor due to stress when the thin film transistor or the like is formed below the spacer, and thus can prevent pixel defects due to spacer stress of the light valve device.

FIGS. 2A, 2B and 2C and FIG.
(A), (B) is sectional drawing which shows the manufacturing method by this invention of the board | substrate 1. FIG. As shown in FIG. 2A, a thin film transistor 3 and a pixel driving electrode 4 connected to a drain electrode of the thin film transistor are provided on the carrier layer 2. Next, FIG.
As shown in (B), an alignment film 5 made of an inorganic material is formed on the entire surface. As a method for forming the alignment film, oblique vapor deposition of silicon monoxide or a pattern such as a groove having a directivity of submicron size is formed on the inorganic thin film by lithography. As shown in the enlarged view of FIG. 2B, the surface of the alignment film 5 is formed with directional irregularities, thereby having an alignment ability for liquid crystal. Next, FIG.
As shown in (C), an organic film 13 such as polyimide having a thickness corresponding to the gap of the liquid crystal cell is applied on the alignment film. FIG. 2C also shows an enlarged cross-sectional view of the state where the alignment film 5 and the organic film 13 are applied.

Next, as shown in FIG. 3A, the organic film 13 is selectively removed by lithography to leave a spacer 6 in a region that does not overlap with the pixel drive electrode 4. A light valve device can be obtained by sandwiching a liquid crystal between the substrate 7 and the substrate 7 whose orientation direction is different by 90 degrees, and further sandwiching both substrates between the polarizing plates 11 and 12. FIG. 5 is a perspective view of the substrate 1 according to the present invention. As in the case of FIG. 1, the transistor 3, the liquid crystal drive electrode 4, the spacer 6, and the like are formed on the carrier layer 2. Alignment film 5
Is formed over the entire surface between the spacer 6 and the liquid crystal drive electrode 4. The spacer 6 is formed at a position covering the transistor 3 of each pixel, and occupies almost no area on the liquid crystal drive electrode 4 that exhibits an electro-optical effect.

In the above description, in a light valve device having an extremely small pixel size, the thickness of the liquid crystal layer, that is, the height of the convex portion is set to 1/10 or less of the width of the pixel drive electrode. It is possible to prevent a decrease in contrast.

[0021]

As described above, according to the present invention, it is possible to realize a light valve device in which the display quality is not deteriorated by the spacer even in a fine pixel of several tens of microns or less. This makes it possible to reduce the size of a high-definition light valve device having a number of pixels of (500 × 500) or more, thereby realizing the miniaturization of a projection display device. In addition, since the spacer is formed by lithography, the distribution is uniform, so that the in-plane distribution of the characteristics of the light valve device is uniform, which contributes to the improvement of image quality. Further, since the destruction of the pixel transistor and the like due to the stress of the spacer can be reduced, the defect due to the pixel defect of the light valve device can be reduced and the production yield can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a schematic sectional view of the present invention.

FIGS. 2A to 2C are explanatory views showing the steps of manufacturing the substrate of the present invention.

FIGS. 3A and 3B are explanatory views showing the steps of manufacturing the substrate of the present invention.

FIG. 4 is an explanatory diagram showing a schematic sectional view of a conventional example.

FIG. 5 is an explanatory view showing a perspective view of an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 First substrate 2 Carrier layer 3 Thin film transistor 4 Liquid crystal drive electrode 5 Alignment film 6 Spacer 7 Second substrate 8 Liquid crystal drive electrode 9 Alignment film 10 Liquid crystal 11 First polarizing plate 12 Second polarizing plate 13 Organic material coating film DESCRIPTION OF SYMBOLS 14 Substrate 15 Carrier layer 16 Thin film transistor 17 Liquid crystal drive electrode 18 Alignment film 19 Spacer 20 Substrate 21 Liquid crystal drive electrode 22 Alignment film 23 Liquid crystal 24 Polarizer 25 Polarizer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/1339 G02F 1/1337 G02F 1/1343 G02F 1/136 G02F 1/13 101 G09F 9/30

Claims (4)

(57) [Claims] Forming a first alignment film by forming a transistor and a pixel electrode connected to a drain electrode of the transistor on a first substrate; obliquely depositing silicon monoxide on the substrate to form a first alignment film; Applying an organic film thereon, selectively removing the organic film by lithography to form a spacer in a region not having the pixel electrode, and forming a liquid crystal drive electrode and a second alignment film on a second substrate. Forming the first substrate, arranging the second substrate at a position where the orientation direction is different by 90 degrees on the first substrate, sandwiching a liquid crystal, and sandwiching the first substrate and the second substrate with a polarizing plate. Manufacturing method of light valve device 2. A method comprising: forming a transistor and a pixel electrode connected to a drain electrode of the transistor on a first substrate; forming an inorganic thin film on the substrate; forming a pattern on the inorganic thin film; Forming an alignment film, applying an organic film on the alignment film, selectively removing the organic film by lithography to form a spacer in a region having no pixel electrode, and forming a spacer on the second substrate. Forming a liquid crystal drive electrode and a second alignment film, disposing the second substrate at a position where the alignment direction is different by 90 degrees on the first substrate and sandwiching a liquid crystal between the first substrate and the second substrate; A method for manufacturing a light valve device, comprising a step of sandwiching a substrate between polarizing plates 3. The method for manufacturing a light valve device according to claim 1, further comprising a step of forming said spacer on said transistor. 4. The method for manufacturing a light valve device according to claim 1, wherein the height of the spacer is set to be 1/10 or less of the width of the pixel electrode.