Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-09-03
2001-09-11
Malinowski, Walter J. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06288763
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an active matrix type liquid crystal display device which has improved visual field angle characteristics and high display quality with less residual image by utilizing bent electrodes.
BACKGROUND OF THE INVENTION
A conventional technology for applying an electric field to a liquid crystal composition layer is proposed, for instance, in Japanese Laid-Open Patent Publication No. 7-36058 and No. 7-159786 in which an electric field is applied to a pair of comb like electrodes formed on a substrate of an active matrix type liquid crystal display device. Heretofore, a display system in which a direction of a primary electric field applied to a liquid crystal composition layer is substantially parallel with a surface of the substrate is referred to as a transverse electric field system.
FIG. 1
shows such a conventional example of a transverse electric field system. In this example, comb like pixel electrodes
5
and
6
are straight and positioned in parallel with one another.
In the above-described transverse electric field system having a conventional pixel electrode structure of
FIG. 1
, it is known that visual field angle characteristics will change drastically with the change of a pretilt angle as shown in FIG.
10
. Thus, in order to achieve good visual angle characteristics in the transverse electric field system, a combination of an alignment film of a very small pretilt angle and liquid crystal is required. According to the experiment, it is desirable that a pretilt angle is less than one (1) degree as shown in FIG.
10
.
However, in a vertical electric field system incorporated in liquid crystal displays most widely used today have a pretilt angle of 3-8 degrees between an alignment film and liquid crystal. The vertical electric field system is a display system wherein a direction of a primary electric field is almost vertical to a surface of a substrate. When an alignment film and liquid crystal with one (1) degree of pretilt are used in a liquid crystal display of the vertical electric field system, a reverse tilt domain will be created by the electric field of video signal lines and pixel electrodes, resulting in a significant deterioration in the display quality.
Because of the foregoing, a set of alignment film and liquid crystal to be used in a liquid crystal display based on the transverse electric field system is different from a set of alignment film and liquid crystal to be used in a liquid crystal display system based on the vertical electric field system. When producing liquid crystal displays of different display systems by the same production facility, alignment films and liquid crystal must be constantly changed, which decreases a production efficiency.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a liquid crystal display device which solves the problems described above.
It is another object of the present invention to provide a liquid crystal display device which is able to incorporate the same alignment film and liquid crystal without regard to the transverse or vertical electric field system, resulting in a dramatic increase in the production efficiency.
This invention is a liquid crystal display device comprising a substrate, scanning lines, video signal lines, thin film transistors provided at crossing points of the scanning lines and the video signal lines, liquid crystal drive electrodes connected to the thin film transistors, an active matrix substrate having at least a portion thereof a common electrode which faces the liquid crystal drive electrodes, a pair of substrates each of which faces the active matrix substrate, a liquid crystal layer held between the active matrix substrate and the pair of substrate, wherein:
[Method 1] when using the liquid crystal of positive dielectric anisotropy (P-type liquid crystal), the video signal line and the pixel electrodes (liquid crystal drive electrode and common electrode) are bent relative to the alignment direction of the liquid crystal within the angle ranging from ±1 to ±30 degrees;
[Method 2] when using the liquid crystal of positive dielectric anisotropy (P-type liquid crystal), the scanning line and the pixel electrodes (liquid crystal drive electrode and common electrode) are bent relative to the alignment direction of the liquid crystal within the angle ranging from ±1 to ±30 degrees;
[Method 3] when using the liquid crystal of negative dielectric anisotropy (N-type liquid crystal), the video signal line and the pixel electrodes (liquid crystal drive electrode and common electrode) are so configured as to be bent relative to the alignment direction of the liquid crystal within the angle ranging from 60 degrees to 120 degrees except 90 degrees;
[Method 4] when using the liquid crystal of negative dielectric anisotropy (N-type liquid crystal), the scanning line and the pixel electrodes (liquid crystal drive electrode and common electrode) are so configured as to be bent relative to the alignment direction of the liquid crystal within the angle ranging from 60 degrees to 120 degrees except 90 degrees; and
[Method 5] a color filter and a black mask are incorporated which are bent in the angle which is the same as that of the video signal line and the scanning line in the above noted methods 1-4.
By incorporating the above described methods 1-4, the liquid crystal molecules rotate in two directions, a left rotation and a right rotation, in a pixel electrode (in the liquid crystal drive electrode and the common electrode) as shown in
FIGS. 4 and 6
when the transverse electric field is applied to the pixel electrodes.
In the conventional configuration of
FIG. 1
, only one direction of rotation motion is generated in the pixel electrode when the transverse electric field is applied to the pixel electrode (the liquid crystal drive electrode and the common electrode) as shown in FIG.
2
. In such a one direction rotation motion, when the pretilt angle is large, disparities of visual field angle property will be induced as shown in FIG.
10
.
In contrast, when two directions of rotation motion, i.e., the left and right rotations, are generated for the liquid crystal molecules in one pixel electrode, disparities of visual angle property will not be induced even if the pretilt angle is large.
Thus, in the liquid crystal display device using the structure of the present invention, the combination of the alignment film and the liquid crystal is freely selected without being limited by the pretilt angle. In other words, the method of the present invention can solve the inherent problems in the conventional transverse electric field system such as an inferior residual image and a response speed.
Further in the present invention, since the pretilt angle will not adversely affect the performance even when the combination of the alignment film and liquid crystal of the conventional transverse electric field system is used, the production line for the vertical electric field system needs not be changed, and thus the productivity will not decrease.
By using the above described methods 1-4 and method 5, it becomes possible to separate the rotation motions of the liquid crystal molecule into two directions in each pixel of colors R, G, and B. Thus, color display with wider visual field angle is achieved.
By using the methods 1-4 noted above, a polarization axis of polarizers to be attached on top and bottom surfaces of the liquid crystal panel can be aligned in a direction either in parallel with major and minor axes of the liquid crystal panel or in perpendicular to the axes. As a result, a determination of cutting angle of the polarizer becomes easy, which improves yield of the polarizer.
Further, by using the methods 1-4 noted above, in an alignment process, a rubbing procedure can be carried out without titling the substrate as shown in FIG.
9
. Hence, frictions by the cloth of a rubbing role are uniformly provided, which prevents unevenness in the rotati
Malinowski Walter J.
Muramatsu & Associates
Obayashiseikou Co., Ltd.
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