Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2002-11-26
2004-03-30
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S039000, C257S059000
Reexamination Certificate
active
06714267
ABSTRACT:
This application claims the benefit of the Korean Application No. P2001-87849 filed on Dec. 29, 2001, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and fabricating method thereof to prevent the generation of afterimage and flickers by increasing a capacitance of a storage capacitor.
2. Discussion of the Related Art
A liquid crystal display device has characteristics of low-voltage driving, low power consumption, full-color realization, lightness and compact size, and the like, thereby becoming applicable to TV, aircraft monitors, PDA and mobile phones, as well as calculators, watches, notebook computers, and personal computers.
Generally, a liquid crystal display device includes a thin film transistor substrate having thin film transistors and pixel electrodes in pixel areas defined by gate and data lines, respectively, a color filter substrate having a color filter layer and a common electrode, and a liquid crystal layer inserted between the two substrates.
In order to drive such a liquid crystal display device, a thin film transistor switches an electrical signal and liquid crystals realize an image in accordance with the signal. Thus, in order to realize a stable image when a liquid crystal display device is driven, the liquid crystals should also be driven while the thin film transistor is turned off. To achieve this, while the thin film transistor is turned on, electric charges are accumulated on a storage capacitor. However, if a capacitance of the storage capacitor charged with the electric charges is not sufficient, afterimage and flickers occur on a screen.
A structure of a liquid crystal display device and a fabricating method thereof according to a related art device are explained by referring to the attached drawings as follows.
Referring to
FIG. 1
, a unit cell of a liquid crystal display device according to a related art device includes gate and data lines
102
a
and
150
crossing each other on a substrate (not shown)and a pixel electrode
108
formed in a pixel area defined by the gate and data lines
102
a
and
150
.
Moreover, the unit cell of the liquid crystal display device further includes a drain electrode
106
b
connected to the pixel electrode
108
through a contact hole
107
a
and a capacitor electrode
106
c
over the gate line
102
a
. In this case, the capacitor electrode
106
c
is connected to the pixel electrode
108
through the other contact hole
107
b.
Referring to
FIG. 2A
, in order to form a unit cell of a liquid crystal display device having the above-explained structure, first of all, a gate electrode
102
and a gate line
102
a
are formed on a substrate
100
.
Subsequently, a gate insulating layer
103
is formed on the gate electrode
102
and gate line
102
a
. An active layer
104
and an ohmic contact layer
105
are formed on the gate insulating layer
103
overlapped with the gate electrode
102
. In this case, a thickness of the gate insulating layer
103
is even all over the gate electrode
102
, gate line
102
a
, and substrate
100
.
Referring to
FIG. 2B
, source and drain electrodes
106
a
and
106
b
are formed on the ohmic contact layer
105
. A capacitor electrode
106
c
is simultaneously formed with the same material forming the source and drain electrodes
106
a
and
106
b
on the gate insulating layer
103
overlapped with the gate line
102
a.
In this case, the capacitor electrode
106
c
, gate line
102
a
, and the gate insulating layer
103
between the capacitor electrode
106
c
and gate line
102
a
constitute a storage capacitor. Hence, the thickness of the gate insulating layer
103
becomes an important variable for capacitance of the storage capacitor. Particularly, if the gate insulating layer
103
is thick, the capacitance of the storage capacitor is reduced so as to generate afterimage and flickers on a screen. Yet, if the gate insulating layer
103
is formed thin to increase the capacitance of the storage capacitor, a parasitic capacitance is generated from the thin film transistor including the gate electrode
102
, source and drain electrodes
106
a
and
106
b
, and the gate insulating layer
103
between them. Hence, the thin film transistor becomes unstable.
Referring to
FIG. 2C
, a passivation layer
107
having contact holes
107
a
and
107
b
is formed on an entire surface of the structure.
Referring to
FIG. 2D
, a pixel electrode
108
is formed on the passivation layer
107
using ITO(indium tin oxide).
In this case, the drain electrode
106
b
and pixel electrode
108
are electrically connected to each other through the contact hole
107
a
, and the capacitor electrode
106
c
and pixel electrode
108
are electrically connected to each other through the other contact hole(‘
107
b
’ in FIG.
1
).
Unfortunately, the liquid crystal according to the related art has the following problem or disadvantage.
If the gate insulating layer is thick, the capacitance of the storage capacitor is decreased so as to generate the afterimage and flickers on the screen. On the contrary, if the gate insulating layer is formed thin so as to increase the capacitance of the storage capacitor, performance of the thin film transistor becomes unstable.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a liquid crystal display device and fabricating method thereof that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a liquid crystal display device and fabricating method thereof to increase a capacitance of a storage capacitor as well as stabilize performance of a thin film transistor.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may 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 objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a liquid crystal display device according to the present invention includes a gate electrode and a gate line on a substrate, a gate insulating layer covering the gate electrode, gate line, and substrate, an active layer formed over the gate electrode so as to leave the gate insulating layer therebetween, source and drain electrodes on the active layer, a capacitor electrode formed over the gate line so as to leave the gate insulating layer therebetween, a passivation layer on the drain and capacitor electrodes so as to have contact holes, and a pixel electrode on the passivation layer.
Preferably, a thickness of the gate insulating layer under the active layer is twice as thick than the thickness of the insulating layer in another area.
More preferably, the gate insulating layer under the active layer is about 4,000 Å thick.
More preferably, the gate insulating layer in another area is about 2,000 Å thick.
Preferably, the liquid crystal display device further includes an ohmic contact layer between the source/drain electrodes and the active layer.
In a further aspect of the present invention, a method of fabricating a liquid crystal display device includes the steps of forming a gate electrode and a gate line on a substrate, depositing a gate insulating layer on the gate electrode, gate line, and the substrate, forming an active layer on the gate insulating layer over the gate electrode, etching the gate insulating layer to a predetermined thickness in all other areas except an area under the active layer, and forming source and drain electrodes on the active area and a capacitor electrode on the gat
Choi Seung Kyu
Im Chul Woo
Dudek James A.
LG. Philips LCD. Co., Ltd.
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