Liquid crystal display

Details Liquid crystal display Liquid crystal display

2000-09-01

2002-11-05

Dudek, James (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

C379S152000

Reexamination Certificate

active

06476895

ABSTRACT:

This application claims the benefit of Korean Patent Application No. 1999-36912, filed on Sep. 1, 1999, which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (hereinafter LCD), and more particularly, an LCD that uses an organic layer as a protection layer.
2. Discussion of the Related Art
An LCD includes a thin film transistor (TFT) array substrate having a plurality of pixels comprising switching devices and pixel electrodes. A color filter substrate comprises color filters corresponding to the respective pixels of the TFT array substrate and common electrodes thereon. Liquid crystals are inserted between the TFT array substrate and the color filter substrate to determine a transmissivity of a light by the voltage difference between the respective pixel electrodes and common electrodes.
An LCD includes a TFT array substrate such that a passivation layer covers switching devices, gate lines and data lines on the substrate. Pixel electrodes connected to the respective electrodes of the switching devices are formed over the passivation layer.
When a black matrix is formed on a color filter substrate of the above-mentioned LCD, the interval between the data line and the pixel electrode (a shading region on a light shielding region) may not be correctly overlapped with the black matrix due to a misalignment formed during the assembly of the TFT array substrate to the color filter substrate. The interval is needed because of a parasitic capacitance that is formed when the data line overlaps the pixel electrode. To solve the misalignment problem the black matrix is formed wider than needed to allow for a sufficient alignment margin. Thus, the aperture ratio is reduced due to the enlargement of the black matrix.
However, if the passivation layer is formed of an organic insulating material of low dielectric constant, the pixel electrode may overlap the data line, because a low dielectric constant will reduce a parasitic capacitance between the pixel electrode and data line. In this case, the aperture ratio is improved since a black matrix of narrow width may be formed.
FIG. 1
shows a schematic layout of a general TFT array substrate.
Referring to
FIG. 1
, data and gate lines (not shown in the drawing) are formed on a substrate. An image display part
11
, where a plurality of switching devices and a plurality of pixels having pixel electrodes
10
are arranged is, located at the central part of the substrate. A peripheral part
12
surrounds the image display part
11
. The peripheral part
12
includes a sealing substance for assembling the TFT array substrate and the color filter substrate, an electrostatic discharge protection circuit, gate pad links connected to gate pads, data pad links connected to data pads and the like.
A data pad part
13
which is to be connected to a driving circuit is formed at an upper side of the peripheral part
12
. A gate pad part
14
which is to be connected to a gate driving circuit is formed at a left side of the peripheral part
12
. The data pad part
13
and the gate pad part
14
are exposed after having been combined with the color filter substrate. Thus, the image display part
11
and the peripheral part
12
surrounding the image display part
11
are overlap the color filter with liquid crystals therebetween. An alignment layer for aligning liquid crystals is formed on the image display part
11
and the peripheral part
12
.
FIG. 2
shows the state of an alignment layer located on an image display part and a peripheral part to explain an LCD according to a related art.
Referring to
FIG. 2
, known devices and wires of an LCD are formed such as gate lines, data lines, and switching devices (such as TFTs) in an image display part, and gate pad links, data pad links, electrostatic discharge protection devices in a peripheral part. These wires and devices are denoted in the drawing as a device layer
20
for simplification.
An organic insulating layer
21
as a passivation layer is formed to cover an entire exposed surface of the image display and peripheral parts. An electrode of each switching device is exposed by etching respective portions of the passivation layer. Then, a pixel electrode
23
is formed and connected to the exposed electrode of the switching device on the organic insulating layer
21
in the image display part.
After an alignment layer
24
formed of an organic material such as polyimide for alignment of liquid crystal molecules has been formed on the exposed surface of the image display and peripheral parts, the substrate is ready for being combined with a color filter substrate.
In the related art, the alignment layer
24
is formed to contact the pixel electrode
23
made of a transparent conductive substance on the image display part. The alignment layer
24
is also formed on the peripheral part and contacts the organic insulating layer
21
. The alignment layer adheres to the transparent conductive layer better than to the organic insulating layer. Such adhesion tendency of the alignment layer relative to the attached substance presents a problem. For example, a portion of the alignment layer
24
formed in the peripheral part at the boundary between the image display and peripheral parts is pushed back in the direction of the pixel electrode
23
in the image display part to form a bump. This causes poor printing including irregular thickness of the alignment layer. Thus, the poorly printed alignment layer causes image stains on the display.
When the alignment layer is printed poorly, the bad part of the alignment layer is removed by dry etching, for example, and a new alignment layer is printed again for reproduction. Unfortunately, the organic insulating layer
21
under the poor alignment layer
29
′ may also be etched as shown in FIG.
3
. The undesired etching changes the surface of the organic insulating layer
21
. Moreover, the surface characteristics of the damaged organic insulating layer
21
deteriorates, resulting in poor adhesion to the alignment layer.
Accordingly, reformation or re-printing of the alignment layer to contact the poorly printed alignment layer still does not cure the problem because of over etching.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a liquid crystal display that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An advantage of the present invention is to provide a liquid crystal display that improves the printing quality of an alignment layer in a peripheral part.
Another advantage of the present invention is to provide a liquid crystal display that improves the adhesion of an alignment layer to a previous layer.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention includes an image display part and a peripheral part wherein the image display part includes: a gate line, a data line crossing the gate line, a switching device connected electrically to the data and gate lines, an organic insulating layer covering an entire surface of the switching device and a pixel electrode on the organic insulating layer and connected to the electrode of the switching device through organic insulating layer; and the peripheral part includes: wires and devices including gate and data pad links and electrostatic discharge devices: and a pattern form is isolated from the wires and devices and an upper part of the pattern is exposed, and an alignment laye

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