Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1996-09-26
2002-01-01
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S132000, C349S134000, C349S133000, C349S156000
Reexamination Certificate
active
06335775
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal device in which a liquid crystal composition is disposed in a gap between a pair of substrates each provided with an electrode and a liquid crystal orientation control layer (particularly, a liquid crystal display device in which a pair of substrates each provided with a transparent electrode and an orientation film in that order are disposed opposite to each other leaving a predetermined gap therebetween and a ferroelectric liquid crystal composition is disposed in the gap) and a manufacturing method therefor.
Recently, studies and developments on application of ferroelectric liquid crystal (FLC; ferroelectric liquid crystal) showing bistability to display devices have been actively promoted. FLC displays are excellent display means having mainly the following features (1) to (3):
(1) High-speed response (1000 times as high as that of the conventional nematic liquid crystal display).
(2) Little visibility angle dependency.
(3) Image memory effect.
Since the ferroelectric liquid crystal display in a bistable mode has a memory effect, it can suppress flicker which is a problem in a CRT (Cathode Ray Tube) or the like, and it can be driven with scanning lines of 1000 or more even by a simple X-Y matrix driving system (driving with TFT: thin film transistors becomes unnecessary). In addition, nematic liquid crystal which is mainly used at present has a problem that its angle of visibility is small, however, the ferroelectric liquid crystal has an advantage that it has a broad angle of visibility because it has uniform molecular orientation and its panel gap is equal to or less than one half of that of a nematic liquid crystal panel.
The FLC display device (ferroelectric liquid crystal display device)
1
using such ferroelectric liquid crystal as described above has a cell structure which is schematically shown in
FIGS. 1 and 2
, for example. The cell structure
1
shown in
FIGS. 1 and 2
mainly comprises a laminate
1
A and a laminate
1
b.
The laminate
1
A is formed by successively laminating, on the inner surface of a transparent substrate
2
a
of glass or the like, a transparent electrode layer
3
a
such as ITO (indium tin oxide: conductive oxide formed of indium doped with tin) or the like and an SiO oblique deposition layer
4
a
serving as a liquid crystal orientation film which has a high contrast and achieves excellent domains, and the laminate
1
B which is formed by successively laminating, on the inner surface of a substrate
2
a
of glass or the like, a transparent electrode layer
3
b
and an SiO oblique deposition layer
4
b.
The laminates
1
A and
1
B are disposed so that the SiO oblique deposition layers
4
a
and
4
b
serving as the liquid crystal orientation films, and then granular spacers
5
are sandwiched between the laminates
1
A and
1
B to achieve a predetermined cell gap d, whereby a liquid crystal cell is fabricated. The peripheral portion of the cell is sealed with an adhesive
7
and the ferroelectric liquid crystal
8
is filled into the cell gap through the inlet port
7
a
and the peripheral portion of the cell is sealed with an adhesive.
For the liquid crystal orientation films
4
a,
4
b,
there has conventionally been used an oblique deposition film of SiO, a rubbing film of polyimide or the like. Particularly, the rubbing film is practically and widely used as an orientation film for liquid crystal display devices at present. When the rubbing film is used as an orientation film, it enhances productivity and facilitates a large-area design. Therefore, at present, many liquid crystal display devices in which rubbing films are used as orientation films have been industrially produced.
However, the rubbing film causes dust to generate at the rubbing time and thus defective picture elements are liable to occur. Further, it is difficult with the rubbing film to provide a pre-tilt angle, and thus there occurs a problem that without such pre-tilt angle, picture elements become defective resulting in reducing the degree of contrast.
On the other hand, when the SiO oblique deposition film is used as the orientation film, it is difficult that pillars to determine the orientation of the liquid crystal are formed uniformly and to a large area. Further, due to the use of a vacuum deposition method, there arises the problem of bad productivity.
The SiO oblique deposition film can be manufactured by a method which is schematically shown in FIG.
3
. That is, in a vacuum deposition device
35
, a deposition source
37
is disposed substantially spotlike in a vacuum chamber
36
, and the deposition is performed while an angle &thgr;
1
of intersection between a line
38
connecting the deposition source
37
and the substrate
2
a
or
2
b
serving as a deposition position and a normal
39
of a deposition plane is set to about 85 degrees (the substrate
2
a
(
2
b
) is disposed within ±&thgr; (for example, ±5°) with respect to the upward and perpendicular direction of the deposition source
37
).
A vacuum pump
41
is linked to the vacuum chamber
36
through a vacuum valve
40
, and a predetermined vacuum degree is achieved under evacuation of the pump. Nitrogen gas is introduced into the vacuum chamber
36
through the vacuum valve
40
in a purging process. The deposition source
37
having SiO
24
mounted in a deposition boat
43
is based on a resistance heating method which applies electric current between resistance heating electrodes
42
, and a deposition speed is controlled by utilizing feedback from a quartz oscillator type thickness monitor
44
.
However, in the case of the above-described oblique deposition method, the precision of the angle &thgr;
1
must be within several degrees in order to make the structure of the SiO oblique deposition film uniform (that is, in order to obtain uniform crystal orientation). The distance between the deposition source
37
and the deposition portion
2
a
(
2
b
) affects the shape of the SiO pillars. Therefore, as the substrate
2
a
(
2
b
) becomes large-sized, the deposition direction is diffused with a solid angle. Therefore, the angle of intersection between the deposition direction and the substrate and the distance from the deposition source are different between the edge and the center of the substrate. As a result, the structure of the oblique deposition film becomes ununiform, and the orientation characteristic does not become uniform, too.
By increasing the distance between the deposition source and the substrate as the substrate becomes large-sized, the problem of the angle or the distance between the two can be temporarily solved. However, in order to increase the distance between the deposition source and the substrate, the chamber of the deposition apparatus must be made large and also the vacuum degree must be increased, resulting in reducing the productivity to a great degree.
Therefore, it has been attempted for a long time that the orientation of the liquid crystal is controlled on the basis of the shape of the surface of the orientation film.
For example, there is a technique in which in consideration of the recognition that the liquid crystal orientation regulating force of a rubbing film is dependent on fine irregularities formed on the surface of the rubbing film or the molecular orientation of the rubbing film, the former effect is modeled and used. As described above, the orientation of the liquid crystal by providing the groove-shaped structure on the surface of the film, and its theoretical interpretation are reported in Physical Review A 24, 5, 2713-2719, (1981), Molecular Crystals and Liquid Crystals 23, 215-231, (1973), Liquid Crystals, 16,6, 1027-1036, (1994), Japanese Journal of Applied Physics 23, 2, 137-141, (1984), Journal of Applied Physics 73, 7, 3299-3304, (1993), or the like.
Besides, it has been attempted that liquid crystal orientation is controlled according to the fine shape of the film. However, a method using photoresist (Japanese Laid-open Patent Application No. Hei
Iwamura Takashi
Kihara Nobuhiro
Nito Keiichi
Shirai Katsuya
Yamamoto Masanobu
Bell Boyd & Lloyd LLC
Ngo Julie
Sikes William L.
Sony Corporation
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