Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-09-18
2004-09-28
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06798484
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a two-domain in-plane switching mode liquid crystal display (IPS-LCD) and, more particularly, to an electrode array of the IPS-LCD to generate a gradient electric field between a pixel electrode and a common electrode.
2. Description of the Related Art
In-Plane Switching mode liquid crystal display (IPS-LCD) has been used or suggested in wide view angle display technology to improve a conventional twisted nematic (TN)-LCD. The IPS-LCD has common electrodes and pixel electrodes formed on a lower glass substrate (TFT substrate) and an in-plane electrode field therebetween is generated to rearrange the LC molecules along the electrode field. Accordingly, the IPS-LCD device can improve viewing angle, contrast ratio and color shift over the conventional twisted nematic device.
Depending on the electrode array of the common electrodes and the pixel electrodes, the IPS-LCD is classified into a single-domain type and a two-domain type.
FIG. 1
is a top view showing an electrode array of a conventional single-domain IPS-LCD
10
. Two parallel gate lines
2
are orthogonal to two parallel data lines
4
to define a rectangular-shaped pixel area, in which a TFT device
5
, a comb-shaped pixel electrode
6
and a herringbone-shaped common electrode
8
are formed. The center wiring
8
a
of the common electrode
8
transversely extends along the center of the pixel area, and the bones
8
b
of the common electrode
8
lengthwise extend form the center wiring
8
a
. The teeth
6
a
of the pixel electrode
6
are disposed in the intervals of the bones
8
b
. When an outer voltage is applied to the IPS-LCD, an in-plane electric field is generated between the adjacent bone
8
b
and tooth
6
a.
The strip-shaped teeth
6
a
are parallel to the strip-shaped bones
8
b
, thus the in-plane electric field generated between the adjacent bone
8
b
and tooth
6
a
is uniform. The uniform electric field indicates that the differential (or gradient) of the strength (including direction) of the electric field at each point to the corresponding planar space is zero. This can make LC molecules have a uniform driving state at the same time, but this needs a higher driving voltage. A way to solve this problem is to reduce the distance between the adjacent bone
8
b
and tooth
6
a
by increasing the number of the teeth
6
a
and the bones
8
b
in the pixel area to lower the driving voltage of the IPS-LCD
10
. However, the line width of the teeth
6
a
and bones
8
b
cannot be narrower than about 3 to 4 microns, thus the aperture ratio of the pixel area is decreasing as the number of the teeth
6
a
and the bones
8
b
is increasing. The single-domain IPS-LCD
10
with the above-described array design of a uniform electric field cannot simultaneously give consideration to the requirements of high aperture ratio and low driving voltage.
A two-domain IPS-LCD is developed for solving a problem of color shift of the single-domain IPS-LCD
10
.
FIG. 2
is a top view showing an electrode array of a conventional two-domain IPS-LCD
20
. Two transverse-extending gate lines
12
and two lengthwise-extending data lines
14
define a pixel area
11
, in which a TFT device
15
, a comb-shaped pixel electrode
16
and a herringbone-shaped common electrode
18
are formed. Each of the teeth
16
a
of the pixel electrode
16
and the bones
18
b
of the common electrode
18
has a chevron-shaped profile and the inclined portion of the chevron-shaped profile is parallel to the adjacent electrode. When an outer voltage is applied to the IPS-LCD
20
, the directions of the electric fields at two sides of the center wiring
18
a
are different to make a part of LC molecules rotate in a counterclockwise direction and another part of LC molecules rotate in a clockwise direction. Therefore, the center wiring
18
a
demarcates the pixel area
11
as an upper single-domain area
11
a
and a lower single-domain area
11
b
. Within each single-domain area
11
a
or
11
b
, the inclined portion of the tooth
16
a
is parallel to the inclined portion of the bone
18
b
and thus a uniform in-plane electric field is generated therebetween. This still encounters the problems of high driving voltage and low aperture ratio.
FIG. 3
is a top view showing the rotation of LC molecules in a uniform electric field of a conventional multi-domain IPS-LCD
30
. In a pixel area, three pixel electrodes
24
a
,
24
b
and
24
c
are disposed in the intervals of four common electrodes
26
a
,
26
b
,
26
c
and
26
d
between two adjacent data lines
22
. Each of the data lines
22
, the pixel electrodes
24
and the common electrodes
26
has a specific profile that is formed by lengthwise connecting at least two “<” shapes. In addition, an orientation layer is formed to cover the pixel area and rubbed in a direction shown as arrow A. When no outer voltage or an outer voltage below the threshold voltage is applied to the IPS-LCD
30
, LC molecules
28
are aligned along the direction shown as arrow A.
Hereinafter, a single-domain area between the pixel electrode
24
b
and the common electrode
26
b
is an example of how the first LC molecule
28
I adjacent to the tip of the “<” shape and the second LC molecule
28
II far away from the tip of the “<” shape rotate. When an outer voltage is applied to generate an in-plane electric field that is lager than a threshold electric field, the directors of the first LC molecule
28
I and the second LC molecule
28
II rotate uniformly to become the LC molecules
28
I′ and
28
II′, respectively. Since the rotating angles, depending on the degree of the applied voltage, of the first LC molecule
28
I and the second LC molecule
28
II are the same, the rotated LC molecules
28
I′ and
28
II′ are parallel to each other. That is, the first LC molecule
28
I and the second LC molecule
28
II simultaneously start rotating, simultaneously stop rotating, and have the same rotating angle. There is no rotating moment generated between the first LC molecule
28
I and the second LC molecule
28
II, and no elastic distorted energy existed between the first LC molecule
28
I and the second LC molecule
28
II. Further, if the applied voltage is smaller than the threshold electric field, all the LC molecules
28
positioned in the single-domain area cannot rotate because they have the same threshold electric field. This still encounters the problems of high driving voltage and low aperture ratio.
SUMMARY OF THE INVENTION
The present invention is to provide an electrode array of a two-domain IPS-LCD to solve the problem caused by the prior art.
In the IPS-LCD, a plurality of lengthwise-extending common electrodes is formed in each pixel area, and each common electrode has a curved profile. A plurality of lengthwise-extending pixel electrodes are formed in each pixel area, and each pixel electrode has a curved profile. The pixel electrodes are disposed it the intervals of the common electrodes, and two adjacent pixel electrode and common electrode form a sub-pixel area. Liquid crystal molecules are positioned within each sub-pixel area where is defined as at least two single-domain areas according to the rotating direction of the liquid crystal molecules. The two adjacent pixel electrode and common electrode within each sub-pixel area are not parallel to each other, thus a gradient in-plane electric field is generated therebetween.
Accordingly, it is a principal object of the invention to provide an IPS-LCD with a lower driving voltage without reducing aperture ratio.
Yet another object of the invention is to provide an IPS-LCD with a gradient electric field within a single-domain area.
It is a further object of the invention to provide an IPS-LCD to decrease the turn-on time.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.
REFERENCES:
patent: 6266116 (2001-07-01), Ohta et al.
patent: 6342937 (2002-01-01), Hi
Lin Sheng-Hsien
Yang Kie-Hsiung
Di Grazio Jeanne Andrea
Hannstar Display Corp.
Kim Robert H.
Rabin & Berdo P.C.
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