Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2001-12-28
2004-12-21
Flynn, Nathan J. (Department: 2826)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S038000, C349S039000, C349S042000, C349S192000, C349S054000, C349S139000
Reexamination Certificate
active
06833882
ABSTRACT:
This nonprovisional application claims priority under 35 U.S.C. § 119(a) on patent Application No. 2001-24592 filed in Republic of Korea on May 7, 2001, which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
1 . Field of the Invention
This invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device and a fabricating method thereof that is capable of increasing an aperture ratio and improving a repair efficiency at the same time. Also, this invention relates to a method of repairing a bad pixel by using the same.
2 . Description of the Related Art
Generally, a liquid crystal display (LCD) controls a light transmittance using an electric field to display a picture. To this end, the LCD includes a liquid crystal panel having liquid crystal cells arranged in a matrix type, and a driving circuit for driving the liquid crystal panel. The liquid crystal panel is provided with pixel electrodes for applying an electric field to each liquid crystal cell, and a common electrode. Typically, the pixel electrode is provided on a lower substrate for each liquid crystal cell, whereas the common electrode is integrally formed on the entire surface of an upper substrate. Each of the pixel electrodes is connected to a thin film transistor (TFT) used as a switching device. The pixel electrode drives the liquid crystal cell, along with the common electrode, in accordance with a data signal applied via the TFT.
Referring to FIG.
1
and
FIG. 2
, a lower substrate
1
of a conventional LCD includes a TFT T arranged at an intersection between a data line
4
and a gate line
2
, a pixel electrode
22
connected to a drain electrode
10
of the TFT, and a storage capacitor S positioned at an overlapping portion between the pixel electrode
22
and the previous gate line
2
′.
The TFT T includes a gate electrode
6
connected to the gate line
2
, a source electrode
8
connected to the data line
4
, and the drain electrode
10
connected, via a contact hole
20
, to the pixel electrode
22
. Further, the TFT T includes a gate insulating film (not shown) for insulating the gate electrode
6
from the source electrode
8
and the drain electrode
10
, and semiconductor layers
14
and
16
for defining a channel between the source electrode
8
and the drain electrode
10
by a gate voltage applied to the gate electrode
6
. Such a TFT T responds to a gate signal from the gate line
2
to selectively apply a data signal from the data line
4
to the pixel electrode
22
.
The pixel electrode
22
is positioned at a cell area divided by the data line
4
and the gate line
2
and is made from a transparent conductive material having a high light transmittance. The pixel electrode
22
is formed on a protective layer (not shown) which is spread on the entire surface of the lower substrate
1
, and electrically connected with the drain electrode
10
through the contact hole
20
formed on the protective layer. The pixel electrode
22
generates a potential difference from a common transparent electrode (not shown) provided at an upper substrate (not shown) by the data signal applied via the TFT T. By this potential difference, a liquid crystal positioned between the lower substrate
1
and the upper substrate (not shown) is rotated due to its dielectric anisotropy. Thus, the liquid crystal allows a light applied, via the pixel electrode
22
, from a light source to be transmitted into the upper substrate.
The storage capacitor S is charged with a voltage in an application period of a gate high voltage to the previous gate line
2
′ while discharging the charged voltage in an application period of a data signal to the pixel electrode, to thereby prevent a voltage variation in the pixel electrode
22
. In this way, because the storage capacitor is used for having the pixel voltage remain stable, its capacitance value should be big enough. To this end, the storage capacitor S is formed in the manner of overlapping with the gate line
2
′ as having a gate insulating film (not shown) therebetween.
In this liquid crystal display device, when there is used a normally white TN mode type liquid crystal, if a defect occurs at the channel between the source electrode
8
and the drain electrode
10
a problem occurs. The pixel cell is displayed as a brightness point because a voltage is not applied to the pixel electrode
22
. Because the bad pixel cell, having the drain electrode
10
and the source electrode
8
opened, is brightly displayed, an observer of the bad pixel cell will readily notice it. Thus a repair will be needed so that the observer will not perceive the bad pixel cell.
One way to repair the bad pixel cell is to connect the neck part of the channel between the source electrode
8
and the drain electrode
10
. The connection may be made by a laser, such that the data signal is always applied from the data line
4
to the pixel electrode
22
. Another way to repair the bad pixel cell is to directly connect the pixel electrode
22
to the data line
4
by welding the pixel electrode
22
with the laser.
In this case, the neighbor pixel cells of the repaired bad pixel cell realize normal color, whereas the bad pixel cell does not receive the desired data such that it is not possible for the liquid crystal display device to realize the complete color.
In
FIG. 2
, there is shown a liquid crystal display device disclosed in Japanese Patent Laid-open Gazette No. Pyung 02-170614 (publication date: Jul. 12, 1990), having a repaired TFT RT besides a main TFT MT and having the channels of the MT and the RT separately formed.
Referring to
FIG. 2
, there are a main TFT MT positioned at the area below the pixel electrode
22
and horizontally in the middle of the pixel electrode
22
, and a repair TFT RT positioned at the area between the data line
4
and the pixel electrode
22
. The main TFT MT includes the source electrode
8
formed so as to extend in a perpendicular direction to the data line
4
(the gate line
2
direction) and the drain electrode
10
connected with the pixel electrode
22
. Also, the repair TFT RT includes the source electrode
28
for repair, which is projected to form from the data line
4
, and the drain electrode
30
for repair, which is not connected with the pixel electrode
22
.
The main TFT MT responds to a gate signal from the gate line
2
to selectively supply a data signal from the data line
4
to the pixel electrode
22
. The pixel electrode
22
is positioned at the cell area divided by the data line
4
and the gate line
2
, and generates a potential difference from a common transparent electrode (not shown) formed on an upper substrate by the data signal supplied via the main TFT MT. By this potential difference, the liquid crystal located between the lower substrate and the upper substrate rotates due to its dielectric anisotropy, and an incident light from a light source is transmitted toward the upper substrate via the pixel electrode
22
.
If a failure of the main TFT MT occurs, the data signal is not supplied to the pixel electrode
22
from the data line
4
by cutting between the source electrode
8
and the data line
4
of the main TFT MT. Then, the pixel electrode
22
is welded by the laser
50
so as to have the drain electrode
30
for repair connected with the pixel electrode
22
. By this arrangement, the data signal from the data line
4
is supplied to the pixel electrode
22
through the repair TFT RT including the source electrode
28
for repair and the drain electrode
30
for repair. As a result, the bad pixel cell realizes the normal color.
The background art having such a TFT repair structure of the liquid crystal display suffers drawbacks.
For example, when repairing the bad pixel cell with a broken wire, the source electrode
8
of the main TFT MT is rather long, being formed along the gate line
2
from the data line
4
. Due to this, a display area decreases. The display area decreases as much as the area where the source electrode
8
is formed of met
Birch & Stewart Kolasch & Birch, LLP
Erdem Fazli
Flynn Nathan J.
LG. Philips LCD Co. Ltd.
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