Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-03-09
2003-07-29
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S152000
Reexamination Certificate
active
06600543
ABSTRACT:
This application claims the benefit of Korean Patent Application No. P99-18569, filed on May 21, 1999, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a liquid crystal display (LCD) and more particularly, to an LCD that has stronger adhesion between a tape carrier package (TCP) and an LCD panel having an organic insulating layer, and a method for manufacturing the same.
2. Description of the Related Art
Generally, an LCD controls the light transmissivity of liquid crystal cells in response to a video signal, thereby displaying a picture that reflects the video signal that is transmitted to the liquid crystal panel in which liquid crystal cells are arranged in a matrix pattern. To achieve this result, the LCD includes drive integrated circuits (ICs) for driving the liquid crystal cells that are arranged in the matrix pattern on the liquid crystal panel. The drive ICs are manufactured in chip form. The drive IC chips are loaded onto the TCP when the LCD is implemented in a Tape Automated Bonding (TAB) system. Alternatively, if the LCD is implemented in a Chips On Glass (COG) system, the drive IC chips are mounted on the liquid crystal panel. The drive IC chips that are implemented in the COG system are electrically connected to a pad portion on the liquid crystal panel by the TCP.
FIG. 1
shows a surface of a conventional liquid crystal panel. The liquid crystal panel
2
has a structure that includes a lower substrate
4
and an upper too, substrate
6
, which are bonded so as to oppose each other. The liquid crystal panel
2
also includes a display portion
8
that is provided with liquid crystal cells arranged in a matrix, and a gate pad portion
12
and a data pad portion
14
arranged such that each is connected between the drive IC chips (not shown) and the display portion
8
. The display portion
8
includes gate lines and data lines arranged on the lower substrate
4
such that they intersect each other, thin film transistors for switching the liquid crystal cells located at the intersections of the gate and data lines, and pixel electrodes that are each connected to the thin film transistors for driving the liquid crystal cells. Also, the display portion
8
has color filters separated by a black matrix on the upper substrate
6
that are the size of a cell region, and a transparent common electrode coated on the surface of the color filters. The lower substrate
4
and the upper substrate
6
are separated from each other by spacers to define a cell gap so that the cell gap. can be filled with liquid crystal material. Also, the lower substrate
4
and the upper substrate
6
are bonded to each other by a sealing material
10
that surrounds the display portion
8
. The gate pad portion
12
and the data pad portion
14
are provided at the edges of the lower substrate
4
which are not overlapped with the upper substrate
6
. The gate pad portion
12
applies a gate driving signal from the gate drive IC chips, which are included in the drive IC chips, to the gate lines of the display portion
8
. The data pad portion
14
transmits a video signal from the data drive IC chips, which are included in the drive IC chips, to the data lines of the display portion
8
.
The liquid crystal panel
2
having the above-described structure uses a protective layer which is disposed on the entire surface of the lower substrate
4
to protect the pixel electrodes and the thin film transistors. The conventional protective layer is an inorganic layer made from SiNx, SiOx and other similar materials. In order to minimize the coupling effect caused by parasitic capacitance, the pixel electrodes and the data lines that are opposite each other have the inorganic protective layer as their center, and must be apart from each other by a constant distance, for example, about 3 to 5 &mgr;m. This is required because the inorganic protective layer has a high dielectric constant. Due to this, the pixel electrode, which determines the aperture ratio, must be small in size.
Conventionally, to make the pixel electrode bigger so that the aperture ratio is greater, an organic material such as benzocyclobutene (BCB), which has a low dielectric constant, is used as the protective layer. For exarmple, in U.S. Pat. No. 5,798,812, there is provided an organic insulating film that covers the pixel area. and the pad area portions of the LCD. Because the organic protective layer has a dielectric constant lower than that of the inorganic protective layer by about 2.7, the pixel electrode can be overlapped with the data line. Thus, the pixel electrode can be enlarged by the amount of overlap between the pixel electrode and the data line so that the aperture ratio of the liquid crystal cell is increased.
The LCD of the TAB system allows the TCP that mounts the drive IC chips to contact the gate and data pad portions. The TAB process forces the TCP to be repeatedly bonded to and then separated from the data and gate pad portions of the liquid crystal panel. In order to prevent the metallic electrodes that are used as the data pads from being damaged due to the repeated bonding and separation between the TCP and the data pad portion of the liquid crystal panel, the data pads that are included in the data pad portion and defined by metallic electrodes are connected to the TCP via transparent electrodes. However, the organic protective layer is weakly bonded with the gate insulating layer and therefore separates easily from the gate insulating layer. As a result, the transparent electrode on the organic protective layer is also easily separated. This problem will be described hereinbelow with reference to
FIGS. 2
to
5
B.
FIG. 2
is a detailed view of a part of the gate pad portion
12
of FIG.
1
.
FIG. 3A
is a cross-sectional view representing the gate pad portion taken along the IIIA-IIIA′ line as shown in FIG.
2
.
FIG. 3B
is a cross-sectional view of the gate pad portion
12
taken along the IIIB-IIIB′ line as shown in FIG.
2
. Referring to
FIGS. 2
,
3
A and
3
B, the gate pads
16
are provided on a lower glass substrate
22
together with the gate lines that are included in the display portion all at the same time. A gate insulating layer
24
and an organic protective layer
26
are sequentially disposed on the entire surface of the lower glass substrate
22
having the gate pads
16
thereon. The gate insulating layer
24
and the organic protective layer
26
are patterned so as to form holes
18
at each of the gate pads
16
. The holes
18
that are located at each gate pad
16
allow the gate pads
16
to be exposed. Transparent electrode patterns
20
are then formed on the organic protective layer
26
such that the transparent electrode patterns
20
are each connected to the corresponding gate pad
16
through the corresponding hole
18
.
Note that the organic protective layer
26
is weakly bonded with the gate insulating layer
24
and so is separated easily from the gate insulating layer
24
when the TCP is separated from the gate pad portion
12
on the liquid crystal panel. Also, the adhesion between the organic protective layer
26
and the gate insulating layer
24
is further weakened by the holes
18
that are defined in the organic protective layer
26
and the gate insulating layer
24
so that almost all of the organic protective layer
26
becomes separated when the TCP is separated from the gate pad portion
12
.
Therefore, the gate pad portion
12
does not have a uniform surface due to the separation of the organic protective layer
26
. Because of this, the TCP becomes weakly bonded with the gate pad portion
12
when it is re-bonded with the gate pad portion
12
so as to decrease the connection area causing increased resistance. Further, the transparent electrode
20
is also separated from the gate pad portion
12
when the organic protective layer
26
becomes separated and exposes the gate pads
16
. Thus, the gate pads
16
are easily damaged or oxidized.
FIG. 4
is a detail view
Jeong Woo Nam
Kim Ki Tae
Kwak Dong Yeung
Lee Gun Hee
Park Kwang Sup
LG Philips LCD Co., Ltd.
Nguyen Dung
Ton Toan
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