Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2003-07-09
2004-11-09
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S129000, C349S136000, C349S187000
Reexamination Certificate
active
06816219
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal panel and a method for manufacturing the same. In particular, the present invention relates to a liquid crystal panel which is suitable for use as a liquid crystal light valve for a projection display (liquid crystal projector) and a method for manufacturing the same.
2. Description of the Related Art
A liquid crystal panel used as a liquid crystal light valve for a liquid crystal display device and even for a liquid crystal projector has a liquid crystal layer sealed between a pair of substrates provided with alignment films thereon. In manufacturing such a liquid crystal panel, an alignment film is formed by rubbing a polyimide or polyamide resin film.
Rubbing, however, causes problems such as formation of scratches and foreign substances on a surface of the resin film (alignment film). In addition, the resin film may not be rubbed uniformly over the entire surface. Furthermore, the resin alignment film easily deteriorates with light. For a liquid crystal projector, its liquid crystal light valve (liquid crystal panel) is irradiated with intense light (incident light) from a light source. Since the intensity of the incident light is increasing nowadays, a resin alignment film is more likely to deteriorate to such a degree as to cause bubbles.
In viewing this, a method for forming an alignment film of an inorganic material such as silicon oxide was proposed and is now used in practice. This method is referred to as oblique deposition in which vapor of an inorganic material such as silicon oxide is supplied at a predetermined oblique angle relative to the normal of a substrate to form an alignment film composed of deposited molecules (molecules of the inorganic material) oriented in the same direction on a surface of the substrate. An alignment film formed by this non-rubbing oblique deposition is free of foreign substances, scratches, or poor alignment. Another advantage of oblique deposition is that the inorganic material used is light resistant to such a level that deterioration of the film is negligible.
Oblique deposition, however, exhibits the following disadvantage when the alignment film formed is used in a liquid crystal panel in TN mode.
When a voltage is applied to drive a liquid crystal panel, the liquid crystal molecules must be preliminary tilted at a predetermined angle (pre-tilt angle) relative to the substrate, in order to align the rising direction of the liquid crystal molecules.
Taking into consideration the fact that a pre-tilt angle from about 5° to 12° is ideal for a TN-mode liquid crystal panel, an alignment film formed by rubbing is more advantageous because it provides a pre-tilt angle from about 2° to 7°. On the other hand, an alignment film formed by oblique deposition of silicon oxide may provide a pre-tilt angle as high as 20° to 30° or 0° (no tilting) depending on the deposition angle. Thus, a TN-mode liquid crystal panel including alignment films formed by oblique deposition of an inorganic material cannot satisfactorily align the rising directions of liquid crystal molecules at a time of voltage application, leading to display defects accordingly.
SUMMARY OF THE INVENTION
In order to solve the foregoing problems, a liquid crystal panel according to the present invention has a liquid crystal layer sealed between a pair of substrates having alignment films thereon. Each of the alignment films is composed of a first deposited layer and a second deposited layer on top of the first deposited layer by oblique deposition of an inorganic material, the deposited molecules of the first deposited layer being aligned substantially perpendicular to the orientation of the deposited molecules of the second deposited layer. In this liquid crystal panel, the first deposited layer has the deposited molecules aligned perpendicular to the orientation of the liquid crystal molecules, and may be formed by oblique deposition that supplies the deposited molecules at a predetermined angle (deposition angle) of, for example, about 60° relative to the normal of the substrate surface. The second deposited layer has the deposited molecules aligned parallel to the orientation of the liquid crystal molecules, and may be formed by oblique deposition that supplies the deposited molecules at a predetermined angle (deposition angle) of about 85° relative to the normal of the substrate surface.
According to the present invention, a method for manufacturing such a liquid crystal panel includes the steps of forming a first deposited layer on the substrates by oblique deposition and forming a second layer on top of the first layer also by oblique deposition. In the second step above, the deposition molecules are supplied onto the surfaces of the substrates from a direction shifted by about 90° from the oblique deposition direction in the first step.
In the liquid crystal panel and the method for manufacturing the liquid crystal panel according to the present invention, each of the alignment films is formed of a first deposited layer, whose deposited molecules are aligned at an angle of 90° to the orientation of the liquid crystal molecules, and a second deposited layer stacked on top of the first deposited layer such that the deposited molecules of the first deposited layer are aligned substantially perpendicular to the orientation of the deposited molecules of the second deposited layer. In such an alignment film, a desirable pre-tilt angle of liquid crystal molecules is achieved by adjusting the thickness of the second deposited layer relative to the thickness of the first deposited layer.
FIG. 1
shows how pre-tilt angles of liquid crystal molecules change depending on the thickness of the second deposited layer (deposition angle of 85°) with respect to the first deposited layer with a thickness of about 40 nm (deposition angle of 60°). As shown in
FIG. 1
, the pre-tilt angles of liquid crystal molecules are substantially proportional to the thickness of the second deposited layer. Based on the graphs shown in
FIG. 1
, the second deposited layer preferably has a thickness of about 0.1 nm to 0.5 nm to achieve a pre-tilt angle of about 5° to 12°, which is ideal for a TN-mode liquid crystal panel.
Thus, the liquid crystal panel and the method for manufacturing the liquid crystal panel according to the present invention are advantageous in that the liquid crystal panel has alignment films of inorganic material resistant to light and provides a pre-tilt angle suitable for a TN-mode liquid crystal panel, for example, by properly controlling the thickness of the two deposited layers constituting each of the alignment films.
As a result, the liquid crystal panel according to the present invention is superior in long-term reliability, prevents display defects at the time of voltage application, and provides a quick response.
REFERENCES:
patent: 4139273 (1979-02-01), Crossland et al.
patent: 4291948 (1981-09-01), Crossland et al.
patent: 5268781 (1993-12-01), Shigeta et al.
patent: 6297865 (2001-10-01), Matsui et al.
Akagi Makoto
Kadota Hisashi
Kurata Tomoki
Depke Robert J.
Duong Tai
Holland & Knight LLP
Ton Toan
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