Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-08-09
2002-07-23
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06424401
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a liquid crystal display panel, and more particularly to a liquid crystal display panel, which is capable of preventing a leakage of liquid crystal caused by an exterior impact.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) controls the light transmissivity of liquid crystal cells arranged in a matrix pattern in response to a video signal to thereby display a picture corresponding to the video signals on a liquid crystal display panel. To this end, the LCD includes a liquid crystal display panel having liquid crystal cells arranged in an active matrix type, and driving integrated circuits (IC's) for driving the liquid crystal cells. The driving IC's are usually manufactured in chip form. The driving IC's is mounted on a tape carrier package (TCP) when they are manufacture by a tape automated bonding (TAB) system while being mounted along the edge of the liquid crystal panel when they are manufactured by a chips on glass (COG) system. In the case of TAB system, the driving IC's are electrically connected to a pad portion provided along the edge of the liquid crystal panel by the TCP. The pad portion is connected to electrode lines connected to each liquid crystal cell of the liquid crystal panel to apply driving signals generated from the driving IC's to each liquid crystal cell.
FIG. 1
is a plan view of a structure of a conventional liquid crystal display panel. In
FIG. 1
, the liquid crystal panel
2
has such a structure that a lower plate
4
and an upper plate
6
are adhered to be opposed in parallel to each other. The liquid crystal panel
2
includes a picture display part
8
having liquid crystal cell arranged in a matrix pattern, a gate pad
12
and a data pad
14
connected between driving IC's (not shown) and the picture display part
8
, a gate link
34
and a data link
16
for connecting the gate pad
12
and the data pad
14
to the picture display part
8
, respectively, and a sealing part provided at the outer circumference of the picture display part
8
so as to bond the lower plate
4
to the upper plate
6
. In the picture display part
8
, data lines to each of which a video signals is applied via the data pad
14
and the data link
16
are intersected with gate lines to each of which a scanning signal is applied via the gate pad
12
and the gate link
34
at the lower plate
4
. At each of the intersections, a thin film transistor (TFT) for switching the liquid crystal cell and a pixel electrode connected to the thin film transistors to drive the liquid crystal cells are provided. Color filters coated separately for each area by a black matrix and a common transparent electrode coated on the surfaces of the color filters are provided at the upper plate
6
. The lower plate
4
and the upper plate
6
having the configuration as describe above are spaced by a spacer to provide a cell gap. The cell gap is filled with a liquid crystal material. The lower plate
4
is adhered to the upper plate
6
by a sealant coated on the seal
10
positioned at the circumference of the picture display part
8
. The gate pad
12
and the data pad
14
are located at the edge of the lower plate
4
which is not overlapped with the upper plate
6
. Each of the gate pad
12
applies a gate signal from the gate driving IC, via the gate link
34
, to the gate lines of the picture display part
8
. Each of the data pad
14
applies a video signal applied from the data driving IC, via the data link
16
, to the data line of the picture display part
8
.
In the liquid crystal panel
2
having the structure as described above, a protective film for protecting the metal electrodes and the thin film transistors are entirely coated on the lower plate
4
. The pixel electrode is formed on the protective film for each cell area. The pixel electrode is a transparent electrode made from indium tin oxide (ITO), and which has a relatively strong durability to the liquid crystal material. Generally, an inorganic material such as SiN
x
or SiO
x
has been used as the protective film. Since the conventional liquid crystal panel includes the inorganic protective film with a high dielectric constant, it has a problem in that a coupling effect caused by a parasitic capacitor between the pixel electrode and the data line having the inorganic protective film therebetween is increased. In order to minimize the coupling effect, it is necessary to keep a space between the two electrodes at a relatively long distance, for example, 3 to 5 &mgr;m and form the pixel electrode having a small area. Accordingly, in the conventional liquid crystal display panel, an aperture ratio depending on the area of the pixel electrode is inevitably lowered to that extent. In order to solve this problem, an organic material, such as benzocyclobutene (BCB), with a relatively low dielectric constant has been used as the protective film. Since this organic protective film has a low dielectric constant of about 2.7 to overlap the pixel electrode with the data line, the area of the pixel electrode can be increased to that extent, thereby improving the aperture ratio.
When the lower and upper plates of the liquid crystal display with such a high aperture ratio are adhered with a sealant, the sealant usually contacts the organic protective film of the lower plate. However, the organic protective film such as an epoxy resin has a strong adhesive characteristic with respect to a glass and the conventional inorganic protective film while having a weak adhesive characteristic with respect to the organic protective film. For this reason, when an impact is applied to the liquid crystal panel, a liquid crystal is leaked through the sealing part having a poor adhesive between the sealant and the organic protective film. Also, the organic protective film has a poor adhesive characteristic with respect to a gate insulating film positioned at the lower part thereof. Accordingly, a crack is generated also between the organic protective film and the gate insulating film by an exterior impact to cause a leakage of the liquid crystal. Hereinafter, such problems of the conventional liquid crystal display will be described in detail with reference to the accompanying drawings.
FIG. 2
is an enlarged view of a crossing part between the data link and the sealant in FIG.
1
. In
FIG. 2
, the data link
16
is provided along with the data pad
14
and the data line (not shown) of the picture display part
8
. A semiconductor layer
18
is extended into the data pad
14
at the lower portion of the data link
16
. The seal
10
coated with a sealant is located in a direction crossing the data link
16
. In this case, because the sealant is coated on the organic protective film, it has a weak adhesive. The data pad
14
contacts a transparent electrode
17
through a contact hole defined at the organic protective film. The transparent film
17
is responsible for protecting a metal electrode as the data pad
14
and for preventing an oxidation of the metal electrode during the repetition of a TCP adhesion required for the TAB process.
FIG. 3A
shows a vertical section taken along the A—A′ line in
FIG. 2
, and
FIG. 3B
shows a vertical section taken along the B—B′ line in FIG.
2
. In
FIGS. 3A and 3B
, the lower plate
4
has such a structure that the gate insulating layer
22
, the semiconductor layer
18
and the data link
16
are sequentially disposed on a lower glass substrate
20
and the organic protective film
24
is entirely coated thereon. The upper plate
6
has such a structure that the color filter and the black matrix
28
are provided on an upper glass substrate
30
and the common transparent electrode
26
is entirely coated thereon. The lower plate
4
and the upper plate
6
having the structure as described above are bonded to each other by the seal
10
. In this case, the seal
10
has a weak adhesive because it is adhered to the organic protective film
24
. Also, sinc
Kang In Byeong
Park Sung Il
Song In Duk
LG. Philips LCD Co. Ltd.
McKenna Long & Aldridge LLP
Schechter Andrew
Ton Toan
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