Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-02-15
2003-04-29
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S040000, C349S139000, C349S187000, C349S141000
Reexamination Certificate
active
06556263
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-7711, filed on Feb. 18, 2000, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color liquid crystal display device, and more particularly to a color 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. Such LCDs typically uses optical anisotropy and spontaneous polarization of a liquid crystal (LC). The LC has thin and long LC molecules, which causes an orientational alignment of the LC molecules. Therefore, alignment direction of the LC molecules is controlled by applying an electric field to the LC molecules. When the alignment direction of the LC molecules is properly adjusted, the LC molecules are aligned and light is refracted along the alignment direction of the LC molecules to display image data. By now, an active matrix (AM) LCD, in which a plurality of thin film transistors and pixel electrodes are arranged in an array matrix, is of particular interest because of its high resolution and superiority in displaying moving pictures. 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. A color IPS-LCD device typically includes a lower substrate where a pixel electrode and a common electrode are disposed, an upper substrate having a color filter, and a liquid crystal interposed between the upper and lower substrates. The color IPS-LCD device has advantages in its improved viewing angle property, such as contrast, gray inversion, and color dispersion properties.
FIG. 1
is a plan view illustrating a conventional color IPS-LCD device. As shown, on a lower substrate or an array substrate (reference
33
of FIG.
2
), gate line
13
and data line
15
are formed perpendicular to each other with a pixel region “P” defined thereby. At a cross point between the gate and data lines
13
and
15
, a switching device
12
is formed. The switching device
12
conventionally employs a thin film transistor (TFT). On the pixel region P, a plurality of pixel electrodes
17
and common electrodes
19
are formed. The pixel and common electrodes
17
and
19
are parallel with and spaced apart from each other on the same plane. Therefore, when a voltage source
10
generates a voltage difference between the pixel and common electrodes
17
and
19
, an in-plane electric field
23
is induced therebetween. The in-plane electric field
23
operates a liquid crystal layer
21
that is interposed between the lower substrate
33
and an upper substrate (reference
25
of FIG.
2
).
At this point, liquid crystal molecules arranged in the gap between the adjacent pixel and common electrodes
17
and
19
are aligned in the same direction as the in-plane electric field
23
. Because each pair of adjacent pixel and common electrodes
17
and
19
involves a corresponding domain of the liquid crystal
21
, a plurality of domains are present in the pixel region “P” such that a wide viewing angle is achieved.
With reference to
FIG. 2
, structure of the conventional color IPS-LCD device is explained in detail. As shown, between the upper and lower substrate
25
and
33
, the liquid crystal layer
21
is interposed. On the lower substrate
33
, the pixel electrodes and common electrodes
17
and
19
are alternately formed with gaps therebetween. On an inner surface of the upper substrate
25
, a color filter
29
, including color filter layer
29
a
and black matrix
29
b
, is formed, and a planar layer
45
is formed to cover the color filter
29
. On exterior surface of the upper substrate
25
, a ground electrode
27
is formed of a transparent conductive material such as indium tin oxide (ITO). The ground electrode
27
prevents exterior static electricity from affecting the liquid crystal layer
21
. Without the ground electrode
27
, the exterior static electricity may electrify the upper substrate
25
and the electrified upper substrate affects the alignment of the liquid crystal molecules. In that case, switching operation of the liquid crystal layer
21
cannot be controlled by data signals and image quality of the LCD device becomes poor.
FIGS. 3A
to
3
E illustrate a sequence of fabricating process for the upper substrate of the conventional IPS-LCD device. At first, as shown in
FIG. 3A
, the upper substrate
25
is prepared. In later steps, the color filter
29
will be formed on a first surface
25
a
of the upper substrate
25
while the ground electrode
27
will be formed on a second surface
25
b
thereof.
Thereafter, as shown in
FIG. 3B
, the ground electrode
27
is formed on the second surface
25
b
of the upper substrate
25
. As explained previously, to form the ground electrode
27
, the transparent conductive material such as indium tin oxide (ITO) is deposited on the upper substrate
25
. Then, the upper substrate
25
including the ground electrode
27
is transferred via a carrier
41
, as shown in FIG.
3
C. At this point, the first surface
25
a
, where the color filter will be formed in a subsequent step, contacts a plurality of loaders
43
of the carrier
41
. The loaders
43
are spaced apart from each other, and each of them rotates to move the upper substrate
25
. Since the first surface
25
a
directly contacts the rotating loader
43
, scratches or defects may occur on the first surface
25
a.
Next, as shown in
FIG. 3D
, the black matrix
29
b
, color filter layer
29
a
, and planar layer
45
are sequentially formed on the first surface
25
a
of the upper substrate
25
, which is transferred via the carrier
41
shown in FIG.
3
C. In detail, chromium oxide (CrO
x
) and chromium (Cr) are deposited on the first surface
25
a
and patterned to form the black matrix
29
b
. Thereafter, the color filter layer
29
a
including red, green, and blue resins “R”, “G”, and “B” is formed on the first surface
25
a
of the upper substrate
25
, using photolithography. The color filter layer
29
a
and black matrix
29
b
are adjacent to each other in an array matrix shape. Then, an insulating material of a transparent polymer or the like is deposited over the first surface
25
a
to form the planar layer
45
.
Next, as shown in
FIG. 3E
, the upper substrate
25
is attached to the lower or array substrate
33
via a sealant
51
such that the IPS-LCD panel
31
is completed. Then a polarizer
47
is formed on the ground electrode
27
of the IPS-LCD panel
31
. The ground electrode
27
is made of the transparent conductive material and attracts contaminants or extraneous matters more than the upper substrate does. That is to say, to prevent the exterior static electricity, the ground electrode
27
is interposed between the upper substrate
25
and the polarizer
47
. However, because the ground electrode
27
of the transparent conductive material attracts extraneous matter more than the upper substrate
25
of a glass material does, the extraneous matter
49
is easily interposed between the polarizer
47
and upper substrate
25
during forming the polarizer
47
on the upper substrate
25
.
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 that is protected from exterior static electricity without interposing a ground electrode between a polarizer and an upper substrate of the IPS-LCD
Duong Tai
Kim Robert H.
LG.Philips LCD Co. , Ltd.
McKenna Long & Aldridge LLP
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