Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-07-31
2003-12-30
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S039000, C349S043000, C349S142000, C349S143000
Reexamination Certificate
active
06671022
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a liquid crystal display device, and more particularly to a multi-domain liquid crystal display device that is capable of forming a multi-domain using a gate line.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) device controls a light transmissivity of liquid crystal cells in accordance with a video signal to display a picture. Such a LCD device has an advantage of small dimension, thin thickness and low power consumption while having a disadvantage of narrow view angle. An active matrix type LCD provided with a switching device for each liquid crystal cell is adaptive for displaying a moving picture. In the active matrix LCD, a thin film transistor (TFT) has been largely used as the switching device.
The active matrix LCD displays a picture corresponding to a video signal such as television signal on picture elements or pixels arranged at each intersection between gate lines and data lines. Each pixel includes a liquid crystal cell controlling a transmitted light amount in accordance with a voltage level of a data signal from the data line. The thin film transistors are formed at intersections between the gate lines and the data lines to switch a data signal to be transferred into the liquid crystal cell in response to a scanning signal from the gate lines.
Recently, there has been suggested a scheme of adjusting an orientation of the liquid crystal cells in a different direction at each of sub-pixels or domain divided into more than two within one pixel in order to compensate for a narrow view angle of the LCD. Such a LCD includes a multi-domain LCD device in which side electrode lines are provided around the pixel electrodes. This multi-domain LCD device drives a liquid crystal by the side electrodes insulated electrically from the pixel electrodes without orientating the liquid crystal cells.
FIG. 1
is a section view showing a structure of a unit pixel included in the conventional multi-domain LCD device. In
FIG. 1
, the unit pixel includes first and second substrates, a plurality of data lines and gate lines arranged horizontally and vertically on the first substrate to divide the first substrate into a plurality of pixel areas, and a thin film transistor at each pixel area on the first substrate. The thin film transistor (TFT) comprising of a gate electrode, a gate insulating film, a semiconductor layer, an ohmic contact layer and a source/drain electrode, a protective film
26
formed on the entire first substrate, a pixel electrode
28
provided on the protective film
26
to be connected to the drain electrode, and side electrodes
24
provided on the gate insulating film in such a manner to be overlapped with a portion of the pixel electrode
28
. The unit pixel further includes a black matrix
30
provided on the second substrate to shut off a light leaked from the gate line, the data line and the thin film transistor, a color filter
32
provided between the black matrices
30
in correspondence with the pixel area, a common electrode
34
provided on the black matrix
30
and the color filter
32
, and a liquid crystal layer
36
between the first and second substrates. The side electrodes
24
in the neighborhood of the pixel and an open area
35
of the common electrode
34
distort an electric field applied to the liquid crystal layer
36
to drive liquid crystal molecules diversely within the unit pixel. In other words, when a voltage is applied to the LCD device, a dielectric energy caused by the distorted electric field positions a liquid crystal director in a desired direction. In this case, the LCD device requires the open area
35
at the common electrode so as to obtain a multi-domain effect. A degree of the electrical field distortion required for a domain division is weak when the open area
35
does not exist in the common electrode
34
or when a width of the open area is small, a time when the liquid crystal director arrives at a stable state is relatively lengthened.
In the LCD device, however, because the side electrodes
24
taking a shape of surrounding the circumference of the pixel electrode
28
are used, an aperture ratio proportional to a size of the pixel electrode
28
is reduced. Accordingly, a brightness of the LCD device is deteriorated. Also, in
FIG. 1
, the side electrodes
24
are formed on the same layer as the data lines. In this case, the data lines are liable to be shorted to the side electrodes
24
, and a line coupling in the data direction is generated, if shorted. In order to overcome this problem, it is necessary to assure a sufficient distance between the data line and the side electrode
24
.
Accordingly, a size of the pixel electrode
28
goes smaller to further reduce an aperture ratio. In addition, the conventional side electrode
24
has a drawback in that, since it is formed in a line type and its width is set to have a value as small as possible (e.g., 6 &mgr;m) in consideration of an aperture ratio, that is, a size of the pixel electrode
26
, it has a large resistance value. As a resistance value of the side electrode
24
is large, a voltage deviation caused by a resistance component thereof increases at the side electrode
24
when applied to a large-dimension panel. Particularly, a common voltage is applied to the side electrode
24
from each side of the panel, and a resistance value of the side electrode
24
is more and more increased to enlarge a voltage deviation as it goes toward the innermost side of the panel. Accordingly, as a potential difference between the pixel electrode
28
and the side electrode
24
is differentiated for each liquid crystal cell, the brightness becomes non-uniform and a flicker and a residual image, etc. are generated to thereby cause a deterioration of picture.
FIG. 2
is a section view showing the structure of a multi-domain LCD device disclosed in the pending Korea Application No. 99-05587 filed by the same applicant. In
FIG. 2
, the multi-domain LCD device includes thin film transistors (TFT's)
6
arranged at each intersection between data lines
2
and gate lines
4
, pixel electrodes
14
connected to drain electrodes
10
of the TFT's
6
, and auxiliary electrode lines
16
provided at the circumferences of the pixel electrodes
14
. Each TFT
6
comprises a gate electrode
12
connected to the gate line
4
, a source electrode
8
connected to the data line
2
, and a drain electrode
10
connected, via a drain contact
11
, to the pixel electrode
14
. The TFT
6
further includes a semiconductor (not shown) for providing a channel between the source electrode
8
and the drain electrode
10
with the aid of a gate voltage applied to the gate electrode
12
. Such a TFT
6
responds to a gate signal from the gate line
4
to selectively apply a data signal from the data line
2
to the pixel electrode
14
. The pixel electrode
14
is formed at a cell area divided by the data line
2
and the gate line
4
, and comprises an electrode made from an indium tin oxide (ITO) material having a high light transmissivity. This pixel electrode
14
generates a potential difference from a transparent electrode (not shown) formed on an upper glass substrate by a data signal applied via the drain contact
11
. At this time, the liquid crystal is rotated by its dielectric anisotrophic property to transmit a light supplied, via the pixel electrode
14
, from a light source toward the upper substrate. The auxiliary electrode line
16
generates a potential difference from the pixel electrode
14
in a scanning interval when a data signal is applied to the liquid crystal cell to adjust an orientation of the liquid crystal, thereby forming a multi-domain. In this case, a common voltage Vcom is applied from an external common voltage generator to the auxiliary electrode line
16
. A boundary line
15
of a matrix formed on the upper substrate is located on the auxiliary electrode line
16
in such a manner that the matrix covers all portions of the auxiliary electro
Ko Doo Hyun
Lee Joun Ho
LG.Philips LCD Co. , Ltd.
McKenna Long & Aldridge LLP
Ton Toan
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