Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-12-28
2004-09-07
Awad, Amr (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C349S141000
Reexamination Certificate
active
06788279
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 1999-67842, filed on Dec. 31, 1999, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device implementing in-plane switching (IPS) where an electric field to be applied to liquid crystal is generated in a plane parallel to a substrate.
2. Discussion of the Related Art
Recently, liquid crystal display (LCD) devices with light, thin, and low power consumption characteristics are used in office automation equipment and video units and the like. Conventionally, the LCD device includes upper and lower substrates that are attached together with a liquid crystal layer interposed therebetween. On exterior surfaces of the upper and lower substrates, polarizers or retardation films are formed.
By configuring the above-mentioned elements selectively, an irradiation of light and a refraction index are changed such that the LCD device has high brightness and contrast ratio. Recently developed LCD device adopts a twisted nematic (TN) liquid crystal. Since the TN liquid crystal has a characteristic of variable transmittance according to viewing angles, it's application to a large-sized LCD device is limited.
The LCD device having the TN liquid crystal has a symmetrical transmittance in directions of right and left and an unsymmetrical transmittance in directions of up and down. The unsymmetrical transmittance results in a reversed image. Therefore, the viewing angle of the LCD device having the TN liquid crystal has a wide viewing angle in directions of right and left, but a narrow view angle in directions of up and down. Driving methods for such LCDs typically include a twisted nematic (TN) mode and a super twisted nematic (STN) mode. Although TN-LCDs and STN-LCDs have been put to practical use, they have a drawback in that they have a very narrow viewing angle. In order to solve the problem of narrow viewing angle, IPS-LCD devices have been proposed. IPS-LCD devices typically include a lower substrate where a pixel electrode and a common electrode are disposed, an upper substrate having no electrode, and a liquid crystal interposed between the upper and lower substrates. The IPS-LCD device has advantages in a contrast ratio, gray inversion, and a color shift that are connected with the viewing angle.
FIGS. 1A and 1B
respectively show on and off states of a conventional IPS-LCD device.
As shown, upper and lower substrates
17
and
19
are spaced apart from each other, a liquid crystal layer
15
a
is interposed between the upper and lower substrates
17
and
19
, and upper and lower polarizers
21
and
23
are respectively formed on each exterior surface of the upper and lower substrates
17
and
19
.
On the lower substrate
19
, a pixel electrode
11
and a common electrode
13
are formed to be parallel with each other and have a gap therebetween. The pixel and common electrodes
11
and
13
include a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO), and an opaque conductive metal.
In
FIG. 1A
, no electric field is applied between the pixel and common electrodes
11
and
13
such that the liquid crystal
15
a
is aligned in its early alignment state. Namely, long axes of the liquid crystal molecules
15
a
are aligned to be parallel with the pixel and common electrodes
11
and
13
.
On the contrary, in
FIG. 1B
, an electric field (not shown) is applied between the pixel and common electrodes
11
and
13
such that the long axes of the liquid crystal molecules
15
a
are aligned to be perpendicular to the pixel and common electrodes
11
and
13
.
Since the IPS-LCD device uses the electric field parallel with the substrate, a wide viewing angle is achieved. Specifically, the viewing angle of the IPS-LCD device is about 70 degrees in direction of up, down, right, and left.
The above-mentioned pixel and common electrodes may have various structures.
FIG. 2
shows a plane view of the conventional IPS-LCD device.
As shown, gate and data lines
31
and
33
cross each other to define a pixel region “P”. In the pixel region P, a common electrode
35
including a plurality of sub-common electrodes
35
b
is formed to be perpendicular to the gate line
31
, and a pixel electrode
37
including a plurality of sub-pixel electrodes
37
b
is also formed to be perpendicular to the gate line
31
. The sub-common and sub-pixel electrodes
35
b
and
37
b
are parallel with each other and have gaps in an alternating pattern. Each end of the sub-pixel electrodes
37
b
is electrically connected with a transverse pixel line
37
a
, while each end of the sub-common electrodes
35
b
is electrically connected with a transverse common line
35
a.
Conventionally, the sub-common electrodes
35
b
and the transverse common line
35
a
are formed in a same layer to communicate with each other. Further, the sub-pixel electrodes
37
b
and the transverse pixel line
37
a
are formed in a same layer to communicate with each other. At this point, each cross point “B” of the sub-electrodes and the transverse lines is formed to have a round with a smooth curve.
Due to the round of the cross point B, an abnormal electric field occurs at the cross point B. Namely, when the electric field is applied between the sub-electrodes in the pixel region P, only the cross point B has a different electric field throughout the pixel region P.
Before a detailed explanation about the above-mentioned abnormal electric field, referring to
FIG. 3A
, a direction of an orientation film will be explained. A first axis
31
a
is a longitudinal direction of the gate line
31
, and a second axis
33
a
is a longitudinal direction of the data line
33
. As shown, a rubbing direction
41
of the orientation film (not shown), which is used to orientate the liquid crystal molecules, have an angle of over 90 degrees with respect to the first axis
31
a
and towards the second axis
33
a.
Now, the previously mentioned problem of the abnormal electric field will be explained in detail with reference to FIG.
3
B.
FIG. 3B
is an enlarged view of a portion “A” of FIG.
2
.
As shown, the sub-pixel electrode
37
b
crosses the transverse pixel line
37
a
in shape of a round “R” such that a distance between the sub-pixel and sub-common electrodes
35
b
and
37
b
varies around the rounded shape. Due to the above-mentioned variance of the distance, when an electric field
43
is applied to the pixel and common electrodes
35
and
37
, an abnormal electric field
45
is formed in a gap “D” between the round R of the sub-pixel electrode
35
b
and the sub-common electrode
37
b
. Since the abnormal electric field
45
has a different direction from the rubbing direction
41
of
FIG. 3A
, the liquid crystal molecules are abnormally aligned in the gap D. The abnormal alignment of the liquid crystal molecules occurs around cross points of the sub-electrodes and the transverse lines throughout the pixel region P of FIG.
2
.
Accordingly, a color dispersion occurs around the pixel region P, and a level of the gray scale changes abnormally in a middle range of the gray scale.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an IPS-LCD device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an IPS-LCD device having a high luminance and a stable gray scale.
In order to achieve the above object, the first preferred embodiment of the present invention provides an in-plane switching mode liquid crystal display device, which includes a gate line and a data line on a first substrate; a pixel region defined by the gate and data lines; a switching device intersection portion between the gate and data lines; a pixel electrode and a common electrode on the first substrate, the pixel electrode having a groove around a cross point between the pixe
Ko Doo-Hyun
Lee Joun-Ho
Awad Amr
LG. Philips LCD Co. Ltd.
McKenna Long & Aldridge LLP
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