Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-04-19
2003-09-23
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06624869
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystal display (LCD) device and a method for manufacturing the same, and more particularly to an in-plane switching type or a lateral electric field type liquid crystal display device and the method for manufacturing the same.
BACKGROUND OF THE INVENTION
A commonly used thin film transistor liquid crystal display device includes a substrate having a plurality of pixel electrodes, an opposite substrate having common electrodes, and a liquid crystal material therebetween. On one of the substrates, a plurality of switching elements, each of which is disposed in a pixel, are disposed to control electric fields which are imparted to the liquid crystal material. An example of switching elements is a metal oxide silicon transistor having a gate electrode, a source electrode, and a drain electrode. The gate electrode receives gate voltages from the gate lines that are arranged on the substrate in a transverse direction. The source electrode is connected to one of data lines crossing the gate lines, which are arranged in a longitudinal direction. The drain electrode extends to form one of the pixel electrodes. When the pixel electrodes and the common electrodes receive voltages by the operation of the corresponding switching elements, the molecules of the liquid crystal material change their orientations in response to the electric fields generated by the potential difference between the pixel electrodes and the common electrodes. The liquid crystal material of the LCD shields or passes light according to the alignment of the liquid crystal molecules to display images.
However, the conventional LCD has a narrow viewing angle which requires selective viewing directions. In order to obtain a wide viewing angle, in-plane switching (IPS) type LCDs are suggested. An example of an IPS LCD is disclosed in U.S. Pat. No. 5,907,379. The IPS LCD has pixel and common electrodes formed on only one substrate. As shown in
FIG. 1
, the pixel electrodes and the common electrodes are disposed alternately in a transverse direction in each pixel so that when the pixel and common electrodes are applied with voltages, a liquid crystal material can be arranged parallel to a substrate.
Referring now to
FIG. 1
, the pixel electrode aligned in a longitudinal direction has two pixel electrode bars
13
and
13
′ every pixel. Two pixel electrode bars
13
and
13
′ are parallel to common electrode bars
21
,
21
′ and
21
″ of the common electrode
20
, and each pixel electrode bar
13
or
13
′ is arranged between two of the common electrode bars
21
,
21
′ and
21
″. Upper ends of the pixel electrode bars
13
and
13
′ are electrically connected to each other by an upper connecting member
15
, whereas lower ends of the pixel electrode bars
13
and
13
′ are electrically connected to each other by a lower connecting member
17
. Thus, the upper connecting member
15
and the lower connecting member
17
along with two pixel electrode bars
13
and
13
′ form a rectangular shape.
The common electrode
20
has three common electrode bars
21
,
21
′ and
21
″ aligned in the longitudinal direction of each pixel. Upper portion and lower portion of the common electrode bars
21
,
21
′ and
21
″ are interconnected respectively by upper common electrode line
23
and lower common electrode line
23
′ to be electrically connected to each other. The common electrode
20
including upper common electrode line
23
and lower common electrode lines
23
′ is extended in the entire pixel area as well as in each pixel, as shown in FIG.
2
.
FIG. 2
shows an electric connecting layout of common electrodes
20
on a substrate of a conventional IPS LCD. The common electrodes
20
of the IPS LCD are arranged parallel to gate lines
40
. It is noted that in
FIG. 2
, the common electrodes
20
are illustrated as lines, but each of them has a ladder shape having a plurality of common electrode bars
21
,
21
′ and
21
″ and common electrode lines
23
and
23
′ connecting the common electrode bars
21
,
21
′ and
21
″ in the transverse direction.
In order to make the common electrode bars
21
,
21
′ and
21
″ in each pixel to receive the same voltages, it is necessary to connect all common electrode bars
21
,
21
′ and
21
″ in the longitudinal direction as well as in the transverse direction. For this purpose, a common shorting bar
31
or
33
is arranged parallel to data lines
50
in the longitudinal direction to be electrically connected with the common electrodes
20
. Accordingly, even though the common shorting bars
31
or
33
supply only one end of each common electrode line or bar with common voltages, the common electrode
20
in each pixel also can be applied with the same common voltages as supplied to one end of each common electrode line or bar since the common electrode bars
21
,
21
′ and
21
″ are interconnected by the common electrode lines
23
and
23
′.
However, in case only one common shorting bar
31
or
33
is used, common voltages supplied to the common electrode bars
21
,
21
′ and
21
″ in pixels remote from the common shorting bar
31
or
33
are lower than the required voltages since each common electrode line
23
or
23
′ has the line resistance. The voltage drop in pixels remote from the common shorting bar
31
or
33
causes a flicker or a crosstalk, and thereby results in a deteriorated image quality of the LCD.
To solve the problem, it can be considered to increase width of the common electrode lines. However, it may decrease an aperture ratio and require additional space to dispose the enlarged common electrode lines.
As another method to solve the problems, it can be also considered to dispose a common shorting bar every pixel row. However, an additional process for forming common shorting bars on a substrate may increase the product cost. Also, the aperture ratio still may be decreased and an additional space may be required for the enlarged common electrode lines.
To solve the above problems and supply effectively each common electrode with common voltage, a widely-used structure disposes common shorting bars
31
and
33
at both sides of a pixel area of the LCD, as shown in FIG.
2
. However, since a large size and a high definition LCD may render a very large voltage difference between a center portion and a peripheral portion of the pixel area, such structure may also cause a flicker or a crosstalk due to the voltage instability, resulting in a deteriorated image quality of the LCD.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an in-plane switching type thin film transistor liquid crystal display device and a method for manufacturing the same that can effectively prevent common voltage drop at each pixel of a pixel area to improve the image quality of the LCD.
It is another object of the present invention to provide an in-plane switching type thin film transistor liquid crystal display device and a method for manufacturing the same that can improve the distribution of common voltages in a pixel area without an additional process and decrease in an aperture ratio
It is other object of the present invention to provide an in-plane switching type thin film transistor liquid crystal display device and a method for manufacturing the same that are adapted to use in a large size and a high definition LCD.
These and other objects are provided, according to the present invention, by an in-plane switching type liquid crystal display device comprising a substrate, a liquid crystal material layer, pixel electrodes, common electrodes, gate lines, and data lines. The liquid crystal display device has common electrode lines connecting common electrode bars in the transverse direction to supply common voltages thereto and common shorting bars arranged parallel to the data lines to be electrically connected to the
Kim Robert H.
McGuireWoods LLP
Rude T. L.
LandOfFree
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