Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-12-15
2004-09-14
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06791653
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 1999-57779, filed on Dec. 15, 1999, which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to an in-plane switching mode liquid crystal display.
2. Discussion of the Related Art
Although demands for large-sized thin film transistor liquid crystal displays (TFT-LCDs) for use in portable TV receivers or notebook computers are great, such large-sized TFT-LCDs have a problem in that contrast ratio varies with viewing angle. For solving such problem, a variety of LCDs, such as twisted nematic (TN) LCDs and multi-domain LCDs have been suggested as having high picture quality and low power consumption. Each of these suggested LCDs have a phase compensation film fitted thereto. However, LCDs cannot solve the problem of viewing angle because liquid crystal molecules that are oriented horizontal to a substrate is oriented almost vertical to the substrate when a voltage is provided to a liquid crystal panel. Accordingly, an in-plane switching mode LCD has been suggested for implementing wide viewing angle, in which the liquid molecules are oriented in a direction almost horizontal to the substrate.
FIG. 1
illustrates an in-plane switching mode LCD in the related art.
As shown in
FIG. 1
, a conventional in-plane switching LCD includes a first substrate having gate lines
1
and data lines
2
running in horizontal and vertical directions. The gate lines
1
and the data lines
2
define a plurality of pixel regions, of which only one is shown in the drawing for convenience of description. In the pixel region, there is a common line
3
in parallel with the gate line
1
, and a thin film transistor at a crossing point of the gate line
1
and the data line
2
. As shown in
FIG. 2
, the TFT includes a gate electrode
4
, a gate insulating film
12
, a source electrode
6
, a drain electrode
7
, a semiconductor layer
5
, and an ohmic contact layer
11
. The gate electrode
4
and the source/drain electrodes
6
and
7
are connected to the gate line
1
and the data line
2
, respectively. The gate insulating film
12
is formed on an entire surface of a first substrate
10
. In the pixel region, there is a common electrode
8
and a data electrode
9
formed parallel to each other for providing an in-plane electric field. The common electrode
8
is formed on the first substrate
10
at the same time as the gate electrode
4
and is connected to the common line
3
. The data electrode
9
is formed on the gate insulating film
12
at the same time as the source/drain electrodes
6
and
7
and is connected to the source/drain electrodes
6
and
7
of the TFT. A protection film
13
and a first orientation film
14
cover the common electrode
8
and the data electrode
9
over the first substrate
10
. A second substrate
15
is provided with a black matrix
16
including chrome for preventing leakage of light to the TFTs, gate lines
1
and data lines
2
, and a color filter layer
17
. Although not shown in the drawing, an overcoat layer for eliminating an uneven surface of the black matrix is formed on the color filter layer and a second orientation film
18
is coated over the color filter layer
17
. A liquid crystal layer
20
is formed between the first and second substrates
10
and
15
.
When there is no voltage provided to the foregoing LCD, the liquid crystal molecules in the liquid crystal layer
20
are oriented along a direction of orientation of the first orientation film
14
and the second orientation film
18
. When a voltage is provided between the common electrode
8
and the data electrode
9
, the liquid crystal molecules are switched to be parallel with the substrate and oriented in a direction perpendicular to a longitudinal direction of the common electrode
8
and the data electrode
9
. As described, since the liquid crystal molecules in the liquid crystal layer
20
are always switched in the same plane, there is no gray level inversion for viewing at angles of up, down, left and right directions.
However, referring to
FIG. 3
, which shows an electric field applied to the liquid crystal layer, the foregoing in-plane switching mode LCD has the following problems.
First, because there is the protection film
13
on the data electrode
9
and the gate insulating film
12
and the protection film
13
on the common electrode
8
, the in-plane electric field applied to the liquid crystal layer
20
is absorbed by the gate insulating film
12
and the protection film
13
, weakening the power of the in-plane electric field and thus reducing the switching speed of the liquid crystal molecules, i.e., a response time of the liquid crystal molecules. Thus, discontinuity disconnection may occur in a moving image displayed by the in-plane LCD.
Second, chrome in the black matrix
16
causes a distortion in an electric field produced by a data signal on the data line
2
. As shown in drawings, the electric field of the data signal directly applies to the data electrode
9
. Namely, the electric field produced by the data signal is affected in the first window between the common electrode
8
and the data electrode
9
. This distorted electric field affects the orientation of the liquid crystal in the first window causing a change in the transmissivity of the liquid crystal at the ends of the window, resulting in a vertical crosstalk.
Third, a wider common electrode
8
may moderate a drop in the shielding effect caused by the position of the common electrode
8
under the gate insulating film
12
and the protection film
13
. However, the wider common electrode reduces the aperture ratio with a consequential drop in luminance.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an in-plane switching mode liquid crystal display that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An advantage of the present invention is to provide an in-plane switching mode liquid crystal display that can shield against signal distortion caused by a Cr (chrome) black matrix.
Another advantage of the present invention is to provide an in-plane switching mode liquid crystal display that can reduce vertical crosstalk and allow a low driving voltage.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an in-plane switching mode LCD includes a first substrate having a switching element, a second substrate, a first electrode and a second electrode on the first substrate, a transparent electrode asymmetrically overlapping the first electrode, and a liquid crystal layer between the first substrate and the second substrate.
In another aspect of the present invention, an in-plane switching liquid crystal display (LCD) device comprises a first substrate; a second substrate; a thin film transistor including: a gate electrode on the first substrate, a gate insulating layer on the gate electrode, a semiconductor layer on the gate insulating layer, and a source electrode and a drain electrode on the semiconductor layer; a gate line connected to the gate electrode extending in a first direction; a data line connected to one of the source and drain electrodes extending in a second direction, the gate line and the data line defining a pixel region; a common electrode on the first substrate on the same layer as the gate line and gate electrode and spaced from the gate electrode; a data electrode connected to
Lee Joun Ho
Park Jeong Ki
Akkapedi P. R.
Kim Robert H.
LG.Philips LCD Co. , Ltd.
McKenna Long & Aldridge LLP
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