Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2002-05-29
2004-06-08
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S043000, C349S141000
Reexamination Certificate
active
06747712
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fringe field switching liquid crystal display device and a method for manufacturing the same and, more particularly, to a fringe field switching liquid crystal display device having improved aperture ratio and transmittance and a method for manufacturing the same.
2. Description of the Prior Art
A fringe field switching liquid crystal display device has been proposed to improve low aperture ratio and transmittance of In-Plane switching liquid crystal display device. In the fringe field switching liquid crystal display device, a counter electrode and a pixel electrode are formed of transparent conductor, and the distance is narrower than that of upper and lower substrates, thereby forming a fringe field between the electrodes.
The fringe field switching liquid crystal display device has a high aperture ratio and transmittance since most of the molecules are operated in a pixel region. However, when an electric field is formed between the counter and the pixel electrodes, liquid crystal molecules with refractive anisotropy are operated to a predetermined direction at the same time. Therefore, it can cause a color shift problem which causes a predetermined color to be expressed according to the viewing angle. The fringe field switching liquid crystal display device having the following structure has been proposed to solve the above and other problems.
Referring to
FIG. 1
, a conventional fringe field switching liquid crystal display device has a structure that a storage capacitance bus line
108
is arranged at the position of bisecting a unit pixel defined by a gate bus line
100
and a data bus line
102
. A thin film transistor
104
as a switching device is arranged at the intersection of the gate bus line
100
and the data bus line
102
, and in the unit pixel, a counter electrode (not shown) is arranged to be overlapped with a pixel electrode
106
.
The pixel electrode
106
is in contact with a source electrode in the thin film transistor
104
through a via hole
105
, comprising a body unit formed in a frame shape and slant slits arranged with a regular distance to divide the body unit into several parts, forming a predetermined angle with the gate bus line
100
. The slant slits are arranged symmetric with respect to the storage capacitance bus line
108
. Therefore, the fringe field is also formed symmetric with respect to the storage capacitance bus line
108
.
And, liquid crystal molecules are arranged symmetric with respect to the storage capacitance bus line
108
, thereby the major axis and the minor axis of liquid crystal molecules are to be seen in any direction of screen. As a result, it is possible to compensate refractive anisotropy of liquid crystal molecule and prevent color shift.
However, the conventional fringe field switching liquid crystal display has a disadvantage that when a cross talk pattern signal is applied to panel, an electric field is formed on the region
112
between the edge of pixel electrode
106
and counter electrode (not shown) and the gate bus line
100
and data bus line
102
, thereby generating undesirable light leakage.
In order to prevent this light leakage, as shown in
FIG. 1
, a method has been proposed that a large black matrix
110
is formed in a pixel region considering coupling margin and viewing angle. However, aperture ratio and brightness are lowered by the large black matrix.
Considering power consumption, it is required to improve aperture ratio, thereby increasing brightness in a BRIGHT state. However, the conventional art has a limitation in remarkably reducing the black matrix on upper substrate to improve aperture ratio of panel.
SUMMARY OF THE INVENTION
Therefore, the present invention has been made to solve the problems and an object of the present invention is to provide a fringe field switching liquid crystal display device having improved aperture ratio and transmittance and a method for manufacturing the same, wherein the pixel structure is modified to prevent light leakage and reduce or eliminate black matrix, having more slits by enlarging the size of pixel electrode.
In order to accomplish the object, the present invention comprises: an upper substrate; a data bus line and a storage capacitance bus line arranged on a lower substrate opposing to the upper substrate to define a unit pixel; a gate bus line arranged at the position of bisecting the unit pixel and to be parallel with the storage capacitance bus line; a thin film transistor arranged on the gate bus line; a counter electrode arranged in the unit pixel; and a pixel electrode overlapped with the counter electrode to form a fringe field and electrically contacted with the thin film transistor through a via hole, wherein the pixel electrode comprises a frame shaped body unit on the edge in the counter electrode and a plurality of slant slits arranged with a regular distance to divide the body unit into several parts, forming a predetermined angle with the gate bus line, and the angle of the slant slits in pixel electrode is symmetric with respect to the gate bus line, and the storage capacitance bus line is overlapped with both the upper edge of pixel electrode in one unit pixel and the lower edge of pixel electrode in the closest unit pixel.
The method for manufacturing a fringe field switching liquid crystal display according to the present invention comprises the steps of: forming a counter electrode on a transparent insulating layer; forming a storage capacitance bus line on upper and lower outer sides of the transparent insulating layer having the counter electrode to define a unit pixel; forming a gate bus line at the position of bisecting the unit pixel; forming an insulating layer on the transparent insulating substrate having the gate bus line and the storage capacitance bus line and then, forming an active layer on the insulating layer over the gate bus line; forming a data bus line and source/drain electrodes extended from the data bus line on the insulating layer having the active layer; forming a protective layer on the source/drain electrodes and on the data bus line and then, forming a via hole exposing a part of the source electrode; and forming a pixel electrode comprising a plurality of slits, being in contact with the source electrode through the via hole.
REFERENCES:
patent: 5822027 (1998-10-01), Shimada et al.
patent: 6014190 (2000-01-01), Kim et al.
patent: 6342937 (2002-01-01), Hiroshi
Lee Seung Hee
Noh Jeong Dong
Boe-Hydis Technology Co., Ltd.
Caley Michael H.
Kim Robert H.
Ladas & Parry
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