Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-12-14
2002-10-01
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S110000, C349S111000
Reexamination Certificate
active
06459465
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-76879, filed on Dec. 15, 2000 in Korea, which is hereby incorporated by reference as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to a liquid crystal panel for a liquid crystal display device implementing In-Plane Switching (IPS) wherein electric field applied to liquid crystal is generated in a plane parallel to a substrate.
2. Discussion of the Related Art
A typical liquid crystal display (LCD) device uses optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite orientation order in alignment resulting from their thin and long shapes. The alignment direction of the liquid crystal molecules can be controlled by supplying an electric field to the liquid crystal molecules. In other words, as the alignment direction of the electric field is changed, the alignment of the liquid crystal molecules also changes. Because incident light is refracted to the orientation of the liquid crystal molecules due to the optical anisotropy of the aligned liquid crystal molecules, image data is displayed.
By now, active matrix LCDs, in which the thin film transistors and the pixel electrodes are arranged in the form of a matrix, are widely used because of their high resolution and superiority in displaying moving images.
FIG. 1
is an exploded perspective view illustrating a typical liquid crystal display device. As shown in the figure, the typical liquid crystal display device includes an upper substrate
5
and a lower substrate
22
and a liquid crystal layer
14
interposed between the upper and lower substrate. A color filter
7
including black matrices
6
and sub-filters
8
are formed on the upper substrate
5
, and a transparent common electrode
18
is formed on the color filter
7
. On the other hand, a pixel region “P”, a pixel electrode
17
in the pixel region “P” and an array line including switching element, i.e., thin film transistor, are formed on the lower substrate
22
. The lower substrate
22
is referred to as an array substrate
22
and a plurality of thin film transistors “T”, i.e., switching element, is formed at every crossing of horizontal gate lines
13
and vertical data lines
15
in a form of an array matrix. The pixel region “P” is defined by a gate line
13
and a data line
15
crossing each other. A transparent conductive material such as indium tin oxide (ITO) is used for the pixel electrode
17
formed in the pixel region “P”. The liquid crystal layer
14
comes to be aligned according to a signal applied thereto by the thin film transistor “T”. An image may be displayed by controlling an amount of light transmitting the liquid crystal layer
14
according to the alignment of the liquid crystal layer.
The above-mentioned liquid crystal display device, in which the liquid crystal is aligned by an electric field applied vertically, has advantages of high transmittance and high aperture ratio. Furthermore, since the common electrode on the upper substrate serves as an electrical ground, the liquid crystal is protected from a static electricity. However, the above-mentioned liquid crystal display device applying the electric field vertically to the liquid crystal has a disadvantage of a narrow viewing angle. To overcome the narrow viewing angle, an in-plane switching (IPS) LCD panel was developed. The IPS LCD panel implements an electric field that is parallel to the substrates, which is different from the Twisted Nematic (TN) or Super Twisted Nematic (STN) LCD panel. A detailed explanation about operation modes of a typical IPS LCD panel will be provided with reference to
FIGS. 2
,
3
A,
3
B, and
4
.
As shown in
FIG. 2
, the upper and lower substrates
5
and
22
are spaced apart from each other, and a liquid crystal is interposed therebetween. The upper and lower substrates
5
and
22
are called a color filter substrate and an array substrate, respectively. Pixel and common electrodes
17
and
18
are disposed on the lower substrate
22
. The pixel and common electrodes
17
and
18
are parallel with each other and spaced apart from each other. The liquid crystal
14
is aligned by a lateral electric field between the pixel and common electrodes
17
and
18
.
FIGS. 3A
to
3
B are views illustrating operations of the liquid crystal for IPS mode at on and off state of a voltage applied.
FIG. 3A
conceptually illustrates “off state” operation modes for a typical IPS LCD device. In the off state, the long axes of the liquid crystal molecules maintain a definite angle with respect to a line that is perpendicular to the pixel and common electrodes
17
and
18
. The pixel and common electrode
17
and
18
are parallel with each other. Herein, the angle difference is 45 degrees, for example.
FIG. 3B
conceptually illustrates “on state” operation modes for the typical IPS LCD device. In the on state, an in-plane electric field, which is parallel with the surface of the lower substrate
22
, is generated between the pixel and common electrodes
17
and
18
. The reason is that the pixel electrode
17
and common electrode
18
are formed together on the lower substrate
22
. The liquid crystal molecules are twisted such that the long axes thereof coincide with the electric field direction. Thereby, the liquid crystal molecules are aligned such that the long axes thereof are perpendicular to the pixel and common electrodes
17
and
18
.
The IPS LCD device uses the lateral electric field
35
because the pixel and common electrodes are formed on the same substrate. The IPS LCD device has a wide viewing angle and low color dispersion. Specifically, the viewing angle of the IPS LCD device is about 70 degrees in direction of up, down, right, and left. In addition, the fabricating processes of this IPS LCD device are simpler than other various LCD devices. However, because the pixel and common electrodes
17
and
18
are disposed on the same plane of the lower substrate, the transmittance and aperture ratio are low. In addition, the IPS LCD device has disadvantages of a relatively slow response time and a relatively small alignment margin of a cell gap. Because of the small alignment margin of a cell gap, the IPS LCD device needs a uniform cell gap. The IPS LCD device has the above-mentioned advantages and disadvantages. Users may or may not select an IPS LCD device depending on the intended use.
Now, with reference to
FIGS. 4
, and
5
A to
5
D, a fabricating process for a conventional IPS LCD device is provided.
FIG. 4
is a plan view illustrating a unit pixel region “P” of a conventional IPS LCD device. As shown, a gate line
50
and a common line
54
are arranged parallel to each other, and a data line
60
is arranged perpendicular to the gate and common lines
50
and
54
. Near a cross point of the gate and data lines
50
and
60
, a gate electrode
52
and a source electrode
62
are disposed. The gate and source electrodes
52
and
62
integrally communicate with the gate line
50
and the data line
60
, respectively. The source electrode
62
overlaps a portion of the gate electrode
52
. In addition, a drain electrode
64
is disposed opposite to the source electrode
62
with an interval between the source and drain electrodes.
A plurality of common electrodes
54
a
are disposed perpendicular to the common line
54
and connected to the common line
54
. The plurality of common electrodes
54
a
are spaced apart from each other with an equal interval between. A first connecting line
66
integrally communicates with the drain electrode
64
. A plurality of pixel electrodes
66
a
are disposed perpendicular to the first connecting line
66
. First ends of the pixel electrodes
66
a
are connected with the first connecting line
66
, and the second ends of the pixel electrodes
66
a
are connected with a second connecting line
68
that is disposed over the common line
54
. The
Dudek James
LG. Philips LCD Co. Ltd.
McKenna Long & Aldridge LLP
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