JPH06273773A - Ferroelectric liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a cell having a uniform thickness and to attain a high contrast and uniform display by specifying the thickness of a liquid crystal layer to be clamped between a pair of light transparent substrates to a specific value or below and arranging adhesive material layers on both sides of spacer members consisting of inorg. insulator film outside display pixels. CONSTITUTION:The inorg. insulator films are used as the spacer members for controlling the cell thickness of the liquid crystal display device having the cell thickness as small as <=2mum The spacers are formed outside the display pixels. The adhesive 5 layers for sticking two sheets of the substrates 2a, 2b facing each other are arranged and adhered on both sides so as to hold the spacers 9 therebetween. A silicon oxide, silicon nitride, silicon carbide, silicon nitride contg. hydrogen, silicon carbide contg. hydrogen, aluminum oxide, etc., are used as the inorg. insulator films. The spacers 9 can be arranged only outside the display pixels by using the inorg. insulator films as the spacer members. An adverse influence on the orientation characteristics and switching characteristics is thus averted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a matrix type large capacity ferroelectric liquid crystal display device having high contrast.

[0002]

2. Description of the Related Art Ferroelectric liquid crystal (FLC) has excellent characteristics such as memory property, high-speed response and wide viewing angle, and its application to liquid crystal display devices with high definition and large display capacity has been extensively studied. ing.

FIG. 5 is a schematic sectional view showing an example of the structure of a ferroelectric liquid crystal cell. Two glass substrates 2a, 2
b are arranged to face each other, and a plurality of transparent signal electrodes S made of indium tin oxide (hereinafter abbreviated as ITO) or the like are arranged in parallel with each other on the surface of one glass substrate 2a, and SiO is formed thereon. _A transparent insulating film 3a made of ₂ or the like is formed. I is on the surface of the other glass substrate 2b.
A plurality of transparent scanning electrodes L made of TO or the like are arranged in parallel to each other in a direction orthogonal to the signal electrodes S, and a transparent insulating film 3b made of SiO ₂ or the like is coated thereon. After the alignment films 4a and 4b are formed on the insulating films 3a and 3b, a uniaxial alignment process such as a rubbing process is performed. As the alignment film, an organic polymer film such as a polyimide film, a nylon film, a polyvinyl alcohol film, or a SiO oblique vapor deposition film is used. These two glass substrates 2a, 2b
After being bonded with an adhesive 5 via a spacer 8 for controlling the cell thickness, a ferroelectric liquid crystal (FLC) 6 is injected into the space sandwiched between the alignment films 4a and 4b. The two glass substrates 2a and 2b thus bonded together have two polarizing plates 7a and 7b arranged so that their polarization axes are orthogonal to each other.
It is sandwiched between.

In a ferroelectric liquid crystal cell, the thickness of a liquid crystal layer sandwiched between a pair of transparent substrates (hereinafter referred to as cell thickness) is 2
It is generally known that it is necessary to make the thickness very thin below μm. As the cell thickness becomes thinner, even slight variations in cell thickness and non-uniformity of the alignment state greatly affect the display quality such as contrast. Therefore,
In the ferroelectric liquid crystal, the control of the cell thickness and the alignment state is an important issue as compared with the conventional liquid crystal of the STN system or the like having a large cell thickness.

Usually, as a means for controlling the cell thickness of a ferroelectric liquid crystal cell, a granular spacer 8 is used for the alignment film 4a,
In general, the method of spraying on 4b and interposing it between a pair of translucent substrates.

As another means, a method of using an organic film such as photosensitive polyimide for the spacer member (Japanese Patent Laid-Open No. 61-73925, Japanese Patent Laid-Open No. 61-196230, Japanese Patent Laid-Open No. 61-208033, Japanese Patent Laid-Open No. 61-241727). , JP-A-62
-280721 etc.) has been proposed

[0007]

However, in the method in which the granular spacers are dispersed, it is difficult to obtain a sufficiently uniform cell thickness due to a large variation in thickness. Further, this method has a problem that the granular spacers 8 are also scattered in the display pixels, and as shown in FIG. 6, the alignment state of the liquid crystal in this portion is different from that in the other portions, and the switching characteristics are also different. It was

In the method using the organic film such as photosensitive polyimide, the problem that the spacer enters the pixel and disturbs the orientation is solved by providing the organic film at a place other than the display pixel. However, the following problems occur in the manufacturing process. That is, in order to manufacture a normal liquid crystal cell, it is necessary to bond the two translucent substrates with an adhesive while pressing at high pressure via a spacer in order to prevent the distance between the two translucent substrates from expanding beyond a predetermined value. At that time, since the organic film has low mechanical strength, the film collapses and there is a problem that a predetermined uniform cell thickness cannot be obtained.

The above problem is not an important problem in the STN system or the like having a large cell thickness, but a ferroelectric liquid crystal having a cell thickness of 2 μm or less has a great influence on display quality such as contrast.

The present invention intends to solve these problems and provide a ferroelectric liquid crystal cell having high contrast and excellent display quality.

[0011]

According to the present invention, in a thin liquid crystal display device having a cell thickness of 2 μm or less, such as a ferroelectric liquid crystal display device, an inorganic insulating film is used as a spacer member for controlling the cell thickness, The spacer is formed outside the display pixel. Further, it is characterized in that adhesive layers for adhering two substrates facing each other are arranged on both sides so as to sandwich the spacer and are bonded. As the inorganic insulator film, silicon oxide, silicon nitride, silicon carbide, silicon nitride containing hydrogen, silicon carbide containing hydrogen, aluminum oxide, or the like can be used.

[0012]

By using the inorganic insulating film as the spacer member, the inorganic insulating film in the display pixel can be removed by a method such as etching, and the spacer can be arranged only outside the display pixel. It is possible to prevent the characteristics from being adversely affected. Furthermore, since the inorganic insulator film has high mechanical strength, the film is not destroyed even when the substrate is pressed for adhesion, and a predetermined cell thickness can be maintained.

In a small-area liquid crystal cell, the use of an inorganic insulating film makes it possible to ensure the uniformity of the cell thickness, but the larger the area, the more difficult it becomes to maintain this uniformity. Therefore, by arranging the adhesive layer on both sides so as to sandwich the spacer, it was possible to further improve the uniformity of the cell thickness. More on this below.

FIG. 2 is a cross-sectional view showing the result of a detailed examination of the substrate bonding method and cell thickness distribution.

First, the adhesive 5 is applied only to the outside of the spacer 9.
When the cells are pasted together, the cell center portion bulges (FIG. 2 (a)). Conversely, when only the inside of the spacer 9 is pasted with the adhesive 5, the cell center portion is dented ( FIG. 2B). This is because the adhesive, which is an organic film, is cured and shrunk while the spacer, which is an inorganic insulator, is not shrunk when adhering while pressing under high pressure. Therefore, as shown in FIG. 2C, the inner side and the outer side of the glass substrate 2a and the outer side of the glass substrate 2a, 2a, 2a, 2a and 2d are adhered to each other with an adhesive 5 so as to sandwich the spacer 9 therebetween.
The distance b, that is, the cell thickness can be kept substantially equal to the film thickness of the spacer 9.

By thus disposing the adhesive layer on both sides so as to sandwich the spacer, the flexure of the substrate caused by shrinkage when the adhesive layer is cured is mitigated, and the uniformity of the cell thickness is further improved. Can be improved.

[0017]

Embodiment 1 The present invention will be described in detail below with reference to the drawings showing the embodiment.

FIG. 1 is a schematic sectional view showing the structure of a ferroelectric liquid crystal cell which is an embodiment of the present invention. The cell of this example has a display area of 1 cm × 1 cm.

Two glass substrates 2a and 2b are arranged to face each other, and ITO is formed on the surface of one glass substrate 2b.
A plurality of transparent scanning electrodes L made of, for example, are arranged in parallel with each other, and a transparent insulating film 3b made of SiO ₂ or the like is formed thereon. An alignment film 4b is formed on the insulating film 3b. As the alignment film, an organic polymer film such as a polyimide film, a nylon film, a polyvinyl alcohol film, or a SiO oblique vapor deposition film is used. On the surface of the other glass substrate 2a, a plurality of transparent signal electrodes S made of ITO or the like are arranged in parallel to each other in a direction orthogonal to the scanning electrodes L, and an inorganic insulator made of SiO ₂ is formed thereon. Forming a film,
Patterning is performed by etching to form the spacer 9. The method for forming the spacer 9 will be described in detail below.

As an inorganic insulating film, OCDty manufactured by Tokyo Ohka
pe7 was used. A SiO ₂ film having a thickness of 1.5 μm can be obtained by applying this OCD type 7 with a spinner at a rotation speed of 1500 rpm and baking it at 350 ° C. for 1 hour. A photoresist is applied on this, and exposure and development are performed using a photomask pattern having a shape surrounding the periphery of the display pixel portion. At this time, in order to form the liquid crystal injection port at the same time, it is preferable to use a pattern with a part removed. After that, etching is performed with hydrofluoric acid so that the SiO ₂ film does not remain in the display pixel, and the inorganic insulating film is left only outside the display pixel so as to surround the periphery of the display pixel. did. The width of the spacer 9 is 20
It is 0 μm.

After the spacer 9 is formed in this manner, a transparent insulating film 3 made of SiO ₂ or the like is further formed on the spacer 9.
An alignment film 4a covered with a and subjected to uniaxial alignment treatment such as rubbing treatment was formed on the insulating film 3a. The two glass substrates 2a and 2b are bonded together with the alignment films 4a and 4b inside, and 1K per cm ² from the outside of the glass substrates.
While pressing with a pressure of g, only the outside of the spacer 9 was bonded with the adhesive 5 while leaving an injection port in a part. As an adhesive, XN-21F manufactured by Mitsui Toatsu was used and applied to a thickness of 5 μm by a usual screen printing method.

Regarding the cell manufactured as described above,
When the cell thickness at each point was measured by an optical interference method, the cell thickness was almost equal to the film thickness of the spacer 9 at all points,
It was possible to obtain 1.45 to 1.55 μm (1.5 ± 0.05 μm). The above process is performed using a polyimide alignment film PSI-A-2101 made by Chisso as an alignment film, SCE-8 made by Merck as a ferroelectric liquid crystal 6 is injected from an injection port, and the injection port is sealed with an adhesive 5. did. When the orientation state was observed, zigzag defects were not generated from the spacers 8 as seen in the cell in which the granular spacers were scattered, and a uniform C2U (C2-uniform) orientation was obtained. When a signal voltage was actually applied and driven, a display with a very high contrast could be obtained because the cell thickness and the alignment state were extremely uniform.

In the method of coating with the spinner shown in this embodiment, the film thickness can be controlled by changing the rotation speed of the spinner, so that the cell thickness can be easily controlled.
Further, the film can be formed by a simple method such as dipping or printing. Other methods for forming the inorganic insulating film include vacuum deposition, sputtering, and electron beam (EB).
Although methods such as vapor deposition and plasma CVD are known, these methods require large-scale equipment and
In order to obtain a thick film of about μm, it is necessary to repeat the film formation, which is industrially problematic.

[0024]

Example 2 A liquid crystal cell having a small area was manufactured in Example 1, but a cell having a display area of 10 cm × 10 cm was manufactured in this example. The larger the area, the more difficult it becomes to keep the cell thickness uniform.

Similar to the first embodiment, two glass substrates 2 are used.
Transparent electrodes S and L, insulating films 3a and 3b, alignment films 4a and 4b, and spacers 9 are formed on a and 2b.

Next, as shown in FIG. 2 (c), the inner side and the outer side are bonded with the adhesive 5 with the spacer 9 interposed therebetween. The width of the adhesive was 0.2 mm both inside and outside the spacer 9, and was applied to a thickness of 5 μm by the screen printing method.

When the cell thickness at each point of the cell thus manufactured was measured by an optical interference method, the cell thickness was 1.45 to 1.55 μm, and good uniformity could be obtained.

Further, a ferroelectric liquid crystal display device manufactured by injecting a ferroelectric liquid crystal as in Example 1 is shown in FIGS. 3 and 4. As a result of observing the alignment state, it was possible to obtain a uniform and high-contrast display as in Example 1 even with a large area.

[0029]

EFFECTS OF THE INVENTION By using the present invention, in a liquid crystal display device having a cell thickness of 2 μm or less like a ferroelectric liquid crystal display device, a uniform thickness can be obtained without adversely affecting switching characteristics and alignment characteristics. A cell can be provided and a high contrast and uniform display can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a ferroelectric liquid crystal cell according to an example of the present invention.

FIG. 2 is a schematic cross-sectional view showing a relationship between a substrate bonding method and a cell thickness distribution.

FIG. 3 is a schematic cross-sectional view showing another embodiment of the present invention.

FIG. 4 is a perspective view of FIG.

FIG. 5 is a schematic cross-sectional view showing the structure of a conventional ferroelectric liquid crystal cell.

FIG. 6 is a diagram showing zigzag defects from a spacer portion.

[Explanation of symbols]

 S signal electrode L scan electrode 2a, 2b glass substrate 3a, 3b insulating film 4a, 4b alignment film 5 adhesive 6 ferroelectric liquid crystal 7a, 7b polarizing plate 8 granular spacer 9 inorganic insulating film spacer

Claims (2)

[Claims] 1. In a liquid crystal display device in which liquid crystal is interposed between a pair of transparent substrates having an electrode film and an alignment film, the thickness of the liquid crystal layer sandwiched between the pair of transparent substrates is 2 μm.
A ferroelectric liquid crystal display device characterized in that a spacer member made of an inorganic insulating film is formed outside the display pixel with a thickness of m or less. 2. A ferroelectric liquid crystal display device according to claim 1, wherein adhesive layers are arranged on both sides of the spacer member.