Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1998-08-19
2002-08-06
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S040000, C349S192000
Reexamination Certificate
active
06429908
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin film transistor panel (or TFT panel) of a liquid crystal display device (or LCD), and more specifically, to a method for reducing the resistivity of a repair line in the TFT panel (or active panel).
2. Description of the Background Art
A conventional liquid crystal display device comprises an active panel and a driving circuit. The active panel, as shown in
FIG. 1
, comprises an upper panel
2
and a lower panel
1
which are arranged to face each other and to be joined together with a liquid crystal material
25
located therebetween. The upper panel
2
comprises a polarizing panel
20
, a transparent substrate
22
, a color filter
23
and a common electrode
24
all of which are disposed on the transparent substrate
22
. The lower panel
1
comprises a polarizing panel
20
, a transparent substrate
21
, a plurality of gate lines
14
disposed on the transparent substrate
21
, a plurality of data lines
15
which are perpendicularly crossed with the gate lines
14
and a pixel electrode
26
and a thin film transistor
16
which are disposed at the intersection portion of the gate lines
14
and the data lines
15
. Pads (not shown in
FIG. 1
) are formed at the ends of the gate lines
14
and the data lines
15
and have a width that is larger than a width of the respective gate and data lines. The lower panel
1
is divided into a displaying area in which the pixel electrode
26
and the thin film transistor
16
are formed and a pad area in which pads connected to the ends of the gate lines
14
and the data lines
15
are formed.
The thin film transistor comprises a gate electrode
31
connected to the gate line
14
, a source electrode
32
connected to the data line
15
and a drain electrode
33
connected to the pixel electrode
26
. Generally, the gate electrode
31
and the gate line
14
are formed during the same processing step. Also, the data line
15
, the source electrode
32
and the drain electrode
33
are formed during the same processing step.
The manufacturing process of the TFT is described with reference to
FIGS. 2
a
-
2
c
. At first, the gate electrode
31
is formed on the transparent substrate
21
of the lower panel
1
. An oxidation layer
37
is then formed on the gate electrode
31
. Then, an insulating layer
30
is formed so as to cover the gate electrode
31
and the oxidation layer
37
. A semiconductor layer
35
is formed on the insulating layer
30
so as to cover the gate electrode
31
. An impurity doped semiconductor layer
34
is formed on the semiconductor layer
35
. After that, the source electrode
32
and the drain electrode
33
are formed on the doped semiconductor layer
34
and the insulating layer
30
. The doped semiconductor layer
34
is patterned by using the source electrode
32
and the drain electrode
33
as a mask. Therefore, the portion of the doped semiconductor layer
34
disposed between the source electrode
32
and the drain electrode
33
is removed. Finally, a passivation layer
36
covering the resulting substrate
21
is formed so that the TFT is completed. The gate line
14
and the gate pad (not shown) are formed at the same time that the gate electrode
31
is formed. The data line
15
and the data pad
40
are formed at the same time that the source electrode
32
and the drain electrode
33
are formed.
In order to increase the resolution of the LCD, many data lines are required. If one data line is broken, then the whole panel can not be used. So, it is necessary prepare an additional line, called a repair line, for repairing a broken line and preventing a broken line from rendering the whole panel unusable. Generally, the repair line is disposed around a periphery of the active panel. The horizontal portion of the repair line is disposed at a location where the gate lines intersect the gate pads and the vertical portion of the repair line is disposed at a location where the data lines intersect the data pads.
FIG. 3
a
shows the active panel having the data pads
40
, data lines
15
and the repair line
60
in detail.
FIG. 3
b
shows another diagram of the active panel according to the conventional art. The repair line
60
comprises a gate line crossing portion
60
a
and a data line crossing portion
60
b
. The data line crossing portion
60
b
of the repair line
60
is formed at the same time that the gate line
14
is formed and the gate line crossing portion
60
a
of the repair line
60
is formed at the same time that the data line
15
is formed. These two portions of the repair line
60
are connected to each other through a contact hole
51
. Referring to the
FIG. 3
c
showing a cross section along the cutting line A—A of
FIG. 3
a
, the manufacturing process of making and connecting the two portions of the repair line
60
in the conventional art is explained.
At first, the data line crossing portion
60
b
of the repair line
60
is formed at the same time that the gate electrode
31
, the gate line
14
, the gate pad (not shown) and a common line
70
are formed. Here, the common line
70
which preferably comprises an anti-electrostatic ground line, prevents an electrostatic capacitance from being formed when the gate lines are separated from each other. Then, a gate insulation layer
30
is deposited thereon. The gate insulation layer
30
has a contact hole
51
exposing an end portion of the data line crossing portion
60
b
of the repair line
60
. Then the gate line crossing portion
60
a
of the repair line
60
is formed at the same time that the source electrode
32
, the drain electrode
33
, the data line
15
and the data pad
40
are formed. The gate line crossing portion
60
a
of the repair line
60
is connected to the exposed portion of the data line crossing portion
60
b
of the repair line
60
through the contact hole
51
.
If a data line
15
is broken by a defect
43
, then the intersection point
45
of the data line
15
and the repair line
60
is connected. So, the data signal applied to the data line
15
having a defect
43
is detoured through the repair line
60
. Hence the broken data line
15
appears to be repaired.
The data line crossing portion
60
b
of the repair line
60
comprises the same material of the gate electrode
31
and the gate line crossing portion
60
a
of the repair line
60
comprises the same material as that of the source electrode
32
and the drain electrode
33
. So, the data line crossing portion
6
b
comprises a low resistance metal such as aluminum or copper. On the other hand, the gate line crossing portion
60
a
comprises a high resistance conductive material such as chromium or indium-tin-oxide (or ITO). Therefore, the resistance of the repair line
60
is related to the sum of the resistance of the two contacts, i.e., the gate material and source material, R
G
+2R
c
+R
S/D
, where R
G
is the resistivity of the gate material, R
c
is a contact resistance at the data line crossing portion
60
b
and the gate line crossing portion
60
a
of the repair line
60
and R
S/D
is the resistivity of the source material. Hence, the resistance of the repair line
60
is higher than any other part of the active panel.
In this structure, if a data line
15
which is located far from the repair line
60
has a defect
43
, then the data line signal traveling the detoured course is significantly delayed by the high resistance of the repair line
60
so that the repair line
60
does not properly work as a repair line. As a result, a repairing area provided by the repair line
60
is limited to only an area located very near to the repair line
60
.
SUMMARY OF THE INVENTION
To overcome the problems described above, the preferred embodiments of the present invention provide a repair line having a low resistance and having an unlimited or maximum repairing area provided by the low resistance repair line.
According to a preferred embodiment of the present invention, an active panel includes a repair line made of a gate ma
Birch Stewart Kolasch & Birch, LLP.
Chowdhury Tarifur R.
LG Philips LCD Co., Ltd.
Sikes William L.
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