Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-10-28
2004-09-21
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S143000
Reexamination Certificate
active
06795142
ABSTRACT:
This application claims the benefit of the Korean Application No. 66819/2001 filed on Oct. 29, 2001, which is hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a structure of a thin film transistor array of a color liquid crystal display, and more particularly, to a substrate structure of a liquid crystal display device suitable for preventing a flicker phenomenon from occurring in a liquid crystal cell of a specific pixel due difference in photo leakage current among liquid crystal cells of red, green and blue pixels.
2. Description of the Background Art
In general, a liquid crystal display device displays a desired picture by supplying data signals with picture information to liquid crystal cells arranged in a matrix such that light transmittance of the liquid crystal cells is controlled. The liquid crystal display device includes a liquid crystal display panel in which liquid crystal cells are arranged in a matrix and driver integrated circuits for driving the liquid crystal cells. The liquid crystal display panel includes a color filter substrate and a thin film transistor array substrate that face each other with liquid crystal filled in between the color filter substrate and the thin film transistor array substrate.
A plurality of data lines are on the thin film transistor array substrate for transmitting data signals from a data driver integrated circuit to the liquid crystal cells. A plurality of gate lines are on the thin film transistor array substrate for transmitting scan signals from a gate driver integrated circuit to the liquid crystal cells. The liquid crystal cells are defined at each intersection of a data line and a gate line. A gate driver integrated circuit sequentially supplies a scan signal to the plurality of gate lines such that the liquid crystal cells, which are in a matrix, are sequentially selected line by line. Data signals are supplied from the data driver integrated circuit to the liquid crystal cells in a selected line of liquid crystal cells.
A common electrode is formed on the color filter substrate and a pixel electrode is formed on the thin film transistor array substrate such that the common electrode and pixel electrode face each other for applying an electric field across the liquid crystal layer. A pixel electrode is formed in each liquid crystal cell and connected to a thin film transistor on the thin film transistor array substrate. A common electrode is integrally formed on the entire surface of the color filter substrate. By controlling a voltage applied to the pixel electrode in each liquid crystal cell while applying a voltage to the common electrode, the light transmittance of the liquid crystal cells can be individually controlled.
In order to control the voltage applied to the pixel electrode in each liquid crystal cell, the thin film transistor is used as a switching device in each liquid crystal cell. A scan signal supplied to the gate electrode of the thin film transistor through a gate line results in a conductive channel being formed between the source electrode and drain electrode of the thin film transistor. Thus, a data signal supplied to the source electrode of the thin film transistor through a data line is applied to the pixel electrode by way of the drain electrode of the thin film transistor.
Elements of a liquid crystal display device will now be described in detail with reference to
FIG. 1A
, which is a plan view of an exemplary liquid crystal cell in a liquid crystal display device. The liquid crystal cell, as shown in
FIG. 1A
, is formed at the intersection of a data line
2
and a gate line
4
. The liquid crystal cell includes a thin film transistor TFT and a pixel electrode
14
connected to a drain electrode
12
of the thin film transistor TFT. A source electrode
8
of the thin film transistor TFT is connected to the data line
2
. A gate electrode
10
of the thin film transistor TFT is connected to the gate line
4
. The drain electrode
12
of the thin film transistor TFT is connected to the pixel electrode
14
through a drain contact hole
16
. The thin film transistor TFT includes an active layer (not shown) which forms a conductive channel between the source electrode
8
and the drain electrode
12
when a scan signal is supplied to the gate electrode
10
through the gate line
4
.
When the conductive channel is formed between the source electrode
8
and the drain electrode
12
in the active layer by the scan signal supplied from the gate line
4
, the data signal supplied to the source electrode
8
through the data line
2
is transmitted to the drain electrode
12
. The pixel electrode
14
is formed in the liquid crystal cell at a region where the liquid crystal cell is positioned. A material, such as indium tin oxide (ITO), with a high light transmittance is used as the pixel electrode
14
. Together with the common electrode (not shown), the pixel electrode
14
applies an electric field to the liquid crystal layer using the data signal supplied through the thin film transistor TFT and via the drain electrode
12
.
The liquid crystal is rotated by a dielectric anisotropy when the electric field is applied across the liquid crystal layer. The rotated liquid crystal allows light emitted from a back light (not shown) through the pixel electrode
14
to be transmitted toward the color filter substrate. The amount of transmitted light is controlled by the voltage value of the data signal.
A storage electrode
20
connected to the pixel electrode
14
through the storage contact hole
22
is deposited on the gate line
4
to form a capacitor
18
. A gate insulation film (not shown), which is deposited during the formation of the thin film transistor TFT, is between the storage electrode
20
and the gate line
4
to isolate the storage electrode
20
from the gate line
4
. The storage capacitor
18
charges to a voltage value of the scan signal during a turn-on period of the thin film transistor when a scan signal is applied to the front stage gate line
4
, and supplies a voltage charge to the pixel electrode
14
during a turn-off period of the thin film transistor to thereby maintain a drive voltage for the liquid crystal cell.
FIG. 1B
is a sectional view of an exemplary thin film transistor TFT taken along line I-I′ of FIG.
1
A. As shown in
FIG. 1B
, the liquid crystal display device includes a thin film transistor array substrate
50
, a color filter substrate
70
and a liquid crystal layer
80
. The color filter substrate
70
is adhered to the thin film transistor array substrate
50
using a sealing material
60
. The liquid crystal layer
80
is positioned between the thin film transistor array substrate
50
and the color filter substrate
70
.
A process for fabricating the thin film transistor of a liquid crystal display device will now be described in detail with reference to FIG.
1
B. First, a metal material, such as Mo, Al or Cr, is deposited on a glass substrate
1
of the thin film transistor array substrate
50
by a sputtering method and patterned through a first mask to form the gate electrode
10
. An insulation material such as SiNx is deposited on the glass substrate
1
and on the gate electrode
10
to form a gate insulation film
30
. A semiconductor layer
32
made of amorphous silicon and an ohmic contact layer
34
made of n+ amorphous silicon with high density phosphor doped therein are successively deposited on the gate insulation film
30
. The semiconductor layer
32
and the ohmic contact layer
34
are then patterned through a second mask to form an active layer
36
of the thin film transistor TFT. A metal material is deposited on the gate insulation film
30
and the ohmic contact layer
34
, and then patterned through a third mask to form a source electrode
8
and a drain electrode
12
of the thin film transistor TFT. The source electrode
8
and the drain electrode
12
are then patterned such that they are isolated and face each other on the upper s
Chae Gee-Sung
Kim Ik-Soo
Chowdhury Tarifur R.
LG. Philips LCD Co. Ltd.
Morgan & Lewis & Bockius, LLP
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