Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-06-14
2003-09-30
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06628364
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a liquid crystal display, and more particularly to a liquid crystal display device that is capable of preventing metal wires from being corroded during its long-term use under the high temperature and high humidity circumstance. The present invention also is directed to a method of fabricating such a liquid crystal display device.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) of active matrix driving system uses thin film transistors (TFT's) as switching devices to display a natural moving picture. Since such a LCD can be made into a smaller device in size than the existent Brown tube, it has been widely used for a monitor for a personal computer or a notebook computer as well as an office automation equipment such as a copy machine, etc. and a portable equipment such as a cellular phone and a pager, etc.
A method of fabricating such an active matrix LCD is classified into substrate cleaning, substrate patterning, aligning film formation, substrate adhesion/liquid crystal injection, packaging and test processes.
In the substrate cleaning process, a cleaner removes an alien substance on the substrates before and after patterning of the upper and lower substrate.
The substrate patterning process is divided into a step of patterning the upper substrate and a step of patterning the lower substrate. The upper substrate is provided with color filters, a common electrode and a black matrix, etc. The lower substrate is provided with signal wires such as data lines and gate lines, etc. A thin film transistor (TFT) is arranged at each intersection between the data lines and the gate lines. A pixel electrode is formed at each pixel area between the data lines and the gate lines to be connected to a source electrode of the TFT.
In the substrate adhesion/liquid crystal injection process, a step of coating an aligning film on the lower substrate and rubbing it is sequentially followed by a step of adhering the upper substrate to the lower substrate, a liquid crystal injection step and an injection hole sealing step.
In the packaging process, a tape carrier package (TCP) mounted with a gate drive integrated circuit (IC) and a data drive IC, etc. is connected to a pad portion on the substrate.
Finally, in the test process, an operation state of a driver IC chip mounted or patterned on the substrate to drive the gate lines and the data lines is tested so as to detect a bad pixel.
In the LCD device, a metal thin film pattern may be corroded during its fabrication process or during its use. Particularly, a corrosion is liable to be generated at a patterned driver circuit, a pad for testing a driver IC mounted onto the TCP, a shorting bar pattern connected to a gate pad and a data pad or an electrode pad exposed by a grinding of the substrate.
The TFT is divided into an amorphous silicon type and a poly silicon type depending on a kind of material used as its semiconductor layer. The amorphous silicon type TFT has advantages of a relatively good uniformity and a stable characteristic while having a drawback of low electric charge mobility. Also, a use of the amorphous silicon type TFT causes a problem in that the peripheral driving circuits are mounted onto the display panel after being manufactured separately. On the other hand, the poly silicon type TFT has advantages in that, since it has a high electric charge mobility, it is not only easy to increase a pixel density, but also the peripheral driving circuits are directly mounted onto the display panel.
Referring to
FIG. 1
, a conventional poly silicon type LCD device includes an upper substrate
2
and a lower substrate
1
joined with each other with having a liquid crystal therebetween, a gate driver IC
9
patterned on the lower substrate
1
to drive a gate line (not shown), and a pad
6
connected, via a link pattern
4
, to the gate driver IC
9
. The edges of the upper substrate
2
and the lower substrate
1
joined with each other are coated with a seal
7
. A liquid crystal is injected into a display area between the upper substrate
2
and the lower substrate
1
. A poly silicon layer is formed on the lower substrate
1
, and the TFT, the data line, the gate line and the pixel electrode, etc. are disposed thereon.
The gate driver IC
9
is directly patterned on the upper substrate
1
positioned at the inside of the seal
7
. The gate driver IC
9
is connected to the gate lines and/or the data lines. The gate driver IC
9
applies a test voltage coupled via the pad
6
and the link pattern
4
to the gate line during the test process.
The pad
6
includes a metal thin film pattern
3
, and a transparent conductive pattern
5
patterned along with a pixel electrode (not shown). The metal thin film pattern
3
is formed on a gate insulating film la made from an inorganic insulating material and is patterned along with source/drain electrodes of the TFT, the data line connected to the source electrode and the link pattern
4
as shown in FIG.
2
. The transparent conductive pattern
5
is connected, via a contact hole
10
defined in a passivation layer made from an inorganic insulating material or an organic insulating material, to the metal thin film pattern
3
.
A crack or a film stripping may be generated between the metal thin film pattern
3
and the transparent conductive pattern
5
of the pad
6
due to an impact, etc. during the fabrication process of the LCD device. When a crack or a film stripping has been generated between the metal thin film pattern
3
and the transparent conductive pattern
5
, moisture is penetrated between the metal thin film pattern
3
and the transparent conductive pattern
5
under the high temperature and high humidity circumstance. If moisture is penetrated between the metal thin film pattern
3
and the transparent conductive pattern
5
, then an electrolytic etching reaction occurs between the metal thin film pattern
3
and the transparent conductive pattern
5
. As a result, the metal thin film pattern
3
is corroded, and corrosion is progressed into the link pattern
4
and the driver IC
9
with the lapse of time.
Referring to
FIG. 3
, the conventional LCD device includes a shorting bar
15
commonly connected to a plurality of pads
11
. Each pad
11
is connected to the data line or the gate line and includes a metal thin film pattern
12
patterned along with the source/drain electrode and a transparent conductive pattern
13
patterned along with the pixel electrode. The transparent conductive pattern
13
is connected, via a contact hole
14
, to the metal thin film pattern
12
.
The shorting bar
15
is connected to a ground voltage source GND during the fabrication process to be responsible for removing a static electricity applied to the liquid crystal display panel. The shorting bar
15
is formed from a metal at the edge portion of the lower substrate
1
corresponding to a non-display area. By the substrate scribing process and the grinding process, the shorting bar
15
is removed simultaneously when an unnecessary area at the edge of the lower substrate
1
is removed.
As shown in
FIG. 4
, a tape carrier package (TCP)
18
is attached to the pad
11
on the lower substrate
1
by a driver IC packaging technique adopting a tape automated bonding (TAB) system. The TCP
18
The TCP
18
is mounted with a data driver IC (or a gate driver IC) and is provided with input pads and output pads. The input pad of the TCP
18
is connected to a printed circuit board (PCB) (not shown). The output pad of the TCP
18
is connected to the pad
11
on the lower substrate
1
. Herein, the input/output pads of the TCP
18
are connected to the PCB and the pads
11
on the lower substrate
1
by an anisotropic conductive film (ACF).
The ground face
16
exists in the side surface of the lower substrate
1
to which the TCP
18
is attached. The ground face
16
is formed by grinding the end of the pad area of the lower substrate
1
using a grinder (not shown) after the substra
Park Jae Deok
Yeo Ju Chun
Dudek James A.
LG.Philips LCD Co. , Ltd.
Morgan & Lewis & Bockius, LLP
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