Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-04-15
2003-12-09
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S139000, C349S038000, C349S138000, C349S043000
Reexamination Certificate
active
06661493
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an In-Plane Switching mode LCD (IPS-LCD) and, more particularly, to an electrode array structure of an IPS-LCD for obtaining a smooth curve in the dark region of the Voltage-Transparency (V-T) diagram.
2. Description of the Related Art
In-plane switching mode LCD (IPS-LCD) has developed for improving the view angle of a conventional twisted nematic LCD (TN-LCD). In an in-plane switching mode LCD (IPS-LCD), common electrodes and pixel electrodes are formed on a lower glass substrate (TFT substrate) and an in-plane electric field therebetween is generated to rearrange the liquid crystal molecules along the in-plane electric field. Accordingly, the IPS-LCD has been used or suggested for improving viewing angle, contrast ratio and color shift.
Depending on designs of the electrode array structure, the IPS-LCD is classified as a single-domain type and a two-domain type.
FIG. 1
is a top view showing an electrode array structure of a single-domain IPS-LCD device
10
according to the prior art. In the IPS-LCD device
10
, two adjacent gate lines
2
and two adjacent data lines
4
are arranged to form an approximately rectangular-shaped pixel area, in which a TFT structure
5
, a comb-shaped pixel electrode
6
, and a comb-shaped common electrode
8
are disposed. The center wiring portion
8
I of the common electrode
8
transversely extends to across the pixel area. The teeth
6
a
of the pixel electrode
6
are disposed in the intervals between the teeth
8
a
of the common electrode
8
. When an outer voltage is applied to the IPS-LCD
10
, an in-plane electric field is generated between the adjacent teeth
6
a
and
8
a
. Also, each of the teeth
6
a
and
8
a
is formed as a strip profile and in parallel to each other, thus the distribution of the electric field generated therebetween is uniform and the liquid crystal molecules can be uniformly driven at the same time. However, this needs a high driving voltage.
For improving color shift of the single-domain IPS-LCD device
10
, a two-domain IPS-LCD device
20
is developed as shown in FIG.
2
. In the two-domain IPS-LCD device
20
, two adjacent gate lines
12
and data lines
14
are arranged in a matrix form to define a pixel area
11
, in which a TFT structure
15
, a comb-shaped pixel electrode
16
and a herringbone-shaped common electrode
18
are disposed. Using the center wiring portion
18
a
of the common electrode
18
as the discrimination, the pixel area
11
is divided into a first sub-pixel area
11
a
and a second sub-pixel area
11
b
. In the first sub-pixel area
11
a
, the first teeth
16
a
of the pixel electrode
16
and the first bones
18
a
of the common electrode
18
are aligned from the lower left toward the upper right. In the second sub-pixel area
11
b
, the second teeth
16
a
and the second bones
18
a
are aligned from the upper left toward the lower right. When an external voltage is applied to the IPS-LCD device
20
, the liquid crystal molecules positioned in different sub-pixel areas
11
a
and
11
b
respectively rotate in counterclockwise direction and in clockwise direction.
In addition, a multi-domain IPS-LCD device
20
′ is developed as shown in FIG.
3
. The tooth of the pixel electrode
16
is formed as a continuous saw-toothed profile extending along lengthwise direction, and the bone of the common electrode
18
is formed as a continuous saw-toothed profile extending along lengthwise direction. For example, as to the pixel electrode
16
, the first tooth
16
a
in the first sub-pixel area
11
a
is parallel to the third tooth
16
c
in the second sub-pixel area
11
b
, and the inclination of the teeth
16
a
and
16
c
is &thgr;. Similarly, the second tooth
16
b
and the fourth tooth
16
c
are in parallel to each other. As to the common electrode
18
, the first bone
18
a
in the first sub-pixel area
11
a
is parallel to the third bone
18
c
in the second sub-pixel area
11
b
, and the inclination of the bones
18
a
and
18
c
is &thgr;. Similarly, the second bone
18
b
and the fourth bone
18
c
are in parallel to each other. However, in the electrode array structure of the IPS-LCD device
20
′, a steep curve is found in the dark region of a Voltage-Transparency (V-T) diagram. This is difficult to subdivide the gray scale.
SUMMARY OF THE INVENTION
The present invention provides an electrode array structure of a multi-domain IPS-LCD to solve afore-mentioned problems.
In in-plane switching mode LCD (IPS-LCD) device, each pixel area of an has at least two common electrodes extending along Y-axis direction and at least a pixel electrode extending along Y-axis direction, in which the pixel electrode is disposed between the two adjacent common electrodes in parallel. The common electrode and the pixel electrode have the same profile that is connected by a first strip-shaped segment, a second strip-shaped segment, a third strip-shaped segment and a fourth strip-shaped segment in sequence. The first segment is not parallel to the second segment, the first segment is not parallel to the third segment, the second segment is not parallel to the fourth segment, and the third segment is not parallel to the fourth segment.
Accordingly, it is a principal object of the invention to provide an electrode array structure to achieve a multi-domain IPS-LCD.
It is another object of the invention to provide the common electrode and the pixel electrode with the continuous saw-toothed profile.
Yet another object of the invention is to provide the common electrode formed by connecting four segments that are not parallel to each other.
It is a further object of the invention to obtain a smooth-tending curve in the dark region of V-T diagram.
Chang Ching Chao
Tanaka Sakae
Hannstar Display Corp.
Intellectual Property Solutions Incorporated
Kim Robert H.
Wang George Y.
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