Liquid crystal display device and method of forming the same

Details Liquid crystal display device and method of forming the same Liquid crystal display device and method of forming the same

2003-10-15

2004-08-24

Ton, Toan (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

C349S146000, C349S043000

Reexamination Certificate

active

06781661

ABSTRACT:

The present invention claims the benefit of Korean Patent Application No. P2001-6516 filed in Korea on Feb. 9, 2001, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device having a high aperture ratio.
2. Discussion of the Related Art
Generally, LCD devices are classified as one of two different types: a transmitting type LCD device and a reflective type LCD device. The transmitting type LCD device has a backlight to serve as a light source, thereby the transmitting type LCD device can display a picture image in low light surroundings. However, the transmitting type LCD device is problematic in that it requires a high power consumption. The reflective type LCD device makes use of ambient light as a light source, thereby requiring a relatively small amount of power consumption. However, the reflective type LCD device is problematic in that it cannot display a picture image in low light surroundings.
To solve the problems of both the transmitting and reflective type of LCD devices, a transflective LCD device is presented. The transflective LCD device can be used as a reflective type or a transmitting type of LCD device as needed since the transflective LCD device has both a reflective part and a transmitting part inside unit pixel region. That is, the transflective LCD device may operate as the reflective LCD device by reflecting of ambient light incident through an upper substrate when the ambient light is sufficient to display an image, and the transflective LCD device may operate as the transmitting LCD device by transmitting light from a backlight source to a liquid crystal layer through an opening part of a reflective electrode when the ambient light is insufficient to display an image. Presently, in order to provide the ambient light to the reflective electrode an area of the reflective or the transflective electrode is increased, thereby increasing an aperture ratio of the transflective LCD device.
FIG. 1A
is a plan view of an LCD device according to the related art.
FIG. 1B
is a sectional view of the LCD device according to the related art along I-I′ of FIG.
1
A. In general, the LCD device includes a TFT substrate as a lower substrate, a color filter substrate as an upper substrate, and a liquid crystal layer between the lower and upper substrates.
In
FIGS. 1A and 1B
, the TFT substrate includes gate lines
2
and data lines
5
, a TFT, and a pixel electrode
7
. The gate lines
2
and the data lines
5
are formed on the lower substrate
1
to cross each other, thereby defining a pixel region. Then, the TFT is formed at a crossing point of the gate lines
2
and the data lines
5
, and the pixel electrode
7
is electrically connected with the TFT. In addition, the pixel electrode
7
occupies most of the area in the unit pixel region. The TFT includes a gate electrode
2
a
, a semiconductor film
4
, a source electrode
5
a
, and a drain electrode
5
b.
A method for manufacturing the LCD device according to the relate art will be described in detail.
A low-resistance conductive metal is deposited on the lower substrate
1
by sputtering processes, and then the gate line
2
and the gate electrode
2
a
are formed on the lower substrate by photolithographic processes. A gate insulating film
3
is formed on an entire surface of the lower substrate including the gate line
2
, and then the semiconductor film
4
is formed above the gate electrode
2
a
. Then, a low resistance metal is deposited on the entire surface of the lower substrate including the gate insulating film
3
, and then the data line
5
and the source/drain electrodes
5
a
and
5
b
are formed by photolithography.
The data line
5
crosses the gate line
2
to define the unit pixel region, and the source/drain electrodes
5
a
and
5
b
are formed on the semiconductor film
4
, thereby forming the TFT. Subsequently, a passivation film
6
is formed on the entire surface of the lower substrate including the TFT at a predetermined depth, and the pixel electrode
7
formed on the passivation film
6
is electrically connected with the drain electrode
5
b
through a contact hole. Accordingly, if the pixel electrode
7
is formed of transparent conductive material such as ITO, the LCD device is formed as the transmitting type. If the pixel electrode
7
is formed of high reflective metal such as Al and Cu, the LCD device is formed as the reflective type. In addition, if the pixel electrode
7
includes a reflective part and a transmitting part, and then a reflective electrode of high reflectivity is formed in the reflective part, and a transmitting electrode connected with the reflective electrode is formed in the transmitting part, whereby the transflective LCD device is formed.
The pixel electrode is patterned by photolithographic and wet etching processes. As shown in
FIG. 1A
, a remaining portion
7
a
of the pixel electrode is not completely removed in regions where material has to be removed during the wet etch, thereby creating an electrical pathway to electrically short adjacent pixel electrodes. The electrical pathway between the adjacent pixel electrodes is caused by a depth of the pixel electrode, condition of the wet etch, and overlap degree between the data and gate lines. Specifically, the pixel electrode is maximized in the unit pixel region to maximize the area of the unit pixel electrode, so that the pixel electrode is close to the adjacent pixel electrode. Therefore, the electrical short between the pixel electrodes is likely to occur.
In case of patterning the reflective electrode as the pixel electrode, any remaining portion of the material for forming the reflective electrode resulting from wet etch processing will be greater than in case of patterning the transmitting electrode as the pixel electrode since the reflective electrode is thicker than the transmitting electrode. Accordingly, in a case of a transistor of a 12.1″ SVGA, the reflective electrode is formed at a depth from 2000 Å to 3000 Å. In addition, if a minimum distance between the reflective electrodes of the adjacent pixels is about 7 &mgr;m, an average total number of electrical pathways generated in one unit substrate is 50 to 70, thereby generating associated defects in 100 unit pixels of the unit substrate. Moreover, the electrical pathway is not removed even though the reflective electrode is sufficiently etched until light leakage generates between the pixel electrodes.
Accordingly, the related art LCD device according to the related art has the following problems. First, since each pixel electrode has to obtain a maximum area within the unit pixel region to increase aperture ratio and reflectivity, electrical shorts are generated between the pixel electrodes, thereby degrading the display quality. Accordingly, if the distance between the adjacent pixel electrodes is reduced, then predetermined corners of the pixel electrode are not etched. Therefore, it is not possible to independently drive the unit pixel electrode. This problem is easily generated when using the reflective electrode as the pixel electrode verses when using the transmitting electrode as the pixel electrode, since the reflective electrode is thicker than the transmitting electrode. Additionally, line width can be reduced by forming the conductive lines of low resistance materials, thereby the distance between the adjacent pixel electrodes becomes shorter resulting in the generation of electrical shorts.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a liquid crystal display device and a method of forming a liquid crystal display device that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an liquid crystal display device and a method of forming a liquid crystal display device having a high aperture ratio, and for preventing the generating

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