Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-06-29
2002-11-12
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S160000
Reexamination Certificate
active
06480252
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to a liquid crystal display having an improved characteristic of viewing angle by modifying a pixel electrode and a common electrode construction respectively.
2. Description of the Related Art
A liquid crystal display is very popular in recent times as a display device in a personal appliance of office automation, a television set etc., since the liquid crystal display is thin and light, and consumes relatively low electric power. The liquid crystal display mainly employs a twist nematic(TN) mode or a super twist nematic(STN) mode for its operation mode.
In the TN mode or the STN mode, the liquid crystal molecules are arranged in such a manner that their longer axes are disposed horizontally with respect to a surface of a substrate while having a twist of ninety degrees when the electric field is not applied. On the contrary, when the electric field is applied, the liquid crystal molecules are arranged in such a manner that their longer axes are disposed vertically with respect to the surface of the substrate and in parallel with the direction of the electric field. In other words, the light is transmitted through and intercepted by such arrangements as described above in the liquid crystal display.
Hereinafter, a conventional liquid crystal display will be described with reference to FIG.
1
.
Referring to
FIG. 1
, a lower substrate
1
and an upper substrate
11
are spaced apart from each other by a predetermined distance. A liquid crystal layer
30
including a plurality of liquid crystal molecules(not shown) is interposed between the lower substrate
1
and the upper substrate
11
.
A thin film transistor
10
of the reversed staggered type and a pixel electrode
7
consisting of a transparent conductor such as an indium tin oxide(ITO) are formed on the inner surface of the lower substrate
1
. The thin film transistor
10
is a switching device for independently operating each pixel. As known in the art, the thin film transistor
10
includes a gate electrode
2
, a gate dielectric film, a semiconductor layer
4
, an etch stopper
5
, an ohmic contact layer
6
, and source/drain electrodes
8
a
and
8
b
. The source electrode
8
a
of the thin film transistor
10
is formed to be in contact with the pixel electrode
7
. A storage electrode
2
a
is formed on the inner surface of the lower substrate
1
in such a manner as to overlap with the pixel electrode
7
. The storage electrode
2
a
is formed simultaneously with the gate electrode
2
, and is disposed on the same plane on which the gate electrode
2
is disposed. A passivation film
9
is formed to cover the thin film transistor
10
.
A black matrix
12
is formed on the inner surface of the upper substrate
11
, so that the black matrix
12
defines a unit pixel. A color filter
13
is formed on the inner surface of the upper substrate
11
, so that the color filter
13
corresponds to the pixel electrode
7
. A dielectric film
14
is formed on the entire inner surface of the upper substrate
11
and on the black matrix
12
and the color filter
13
, so as to protect the color filter
13
and to improve evenness of the inner surface of the upper substrate
11
. A common electrode
15
consisting of a transparent conductor such as an ITO film is formed on the dielectric film
14
.
The conventional liquid crystal display having the construction as described above is operated as follows. When the thin film transistor
10
is turned on, a data signal is applied to the pixel electrode
7
, so that an electric field E is generated between the pixel electrode
7
and the common electrode
12
. Then, the liquid crystal molecules are rearranged in such a manner that their long axes are disposed in parallel with the direction of the electric field E. In result, the light is partially transmitted through and partially intercepted by the liquid crystal molecules, so that a predetermined image is displayed. In this case, the direction of the electric field E is perpendicular to the surfaces of the substrates
1
and
11
.
However, in the conventional liquid crystal display employing the TN mode or the STN mode, since the transmittance changes according to the direction of viewing the screen from a viewer, the conventional liquid crystal display has an inferior characteristic of viewing angle.
That is, the liquid crystal molecules exhibit a refractive anisotropy, since they have different lengths of the longer axes and the shorter axes. Therefore, in the case where is employed the liquid crystal molecules having a positive dielectric anisotropy, the liquid crystal molecules are arranged so that their longer axes are disposed vertically to the surfaces of the substrates by the electric field. Then, the viewer can see the shorter axes of the liquid crystal molecules when he views the screen in the direction of the normal line to the surface. In the meantime, the viewer can see slanted axes of the liquid crystal molecules when he views the screen from the lateral side of the screen. Accordingly, the viewing angle changes according to the direction of viewing the screen. Additionally, leakage of light occurred at the lateral sides of the screen at which the viewer can see the slanted axes of the liquid crystal molecules. Therefore, the conventional liquid crystal display employing the TN mode or the STN mode has an inferior characteristic of the viewing angle.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and it is an object of the present invention to provide a liquid crystal display having an improved viewing angle characteristic.
In order to achieve the above object, the present invention provides a liquid crystal display having: upper and lower substrates opposed to each other and spaced from each other by a predetermined distance; a liquid crystal layer interposed between the upper and the lower substrates, the liquid crystal layer including a plurality of liquid crystal molecules; a pixel electrode formed at a portion of an inner surface of the lower substrate corresponding to a pixel area, the pixel electrode having an uneven surface including first convex portions and first concave portions; and a common electrode formed at a portion of an inner surface of the upper substrate corresponding to the pixel electrode, so as to form an electric field together with the pixel electrode, the common electrode having an uneven surface including second convex portions and second concave portions.
REFERENCES:
patent: 5013141 (1991-05-01), Sakata
patent: 5644372 (1997-07-01), Shinjo et al.
patent: 5666179 (1997-09-01), Koma
patent: 5907380 (1999-05-01), Lien
patent: 6292240 (2001-09-01), Kamiya et al.
patent: 03160421 (1991-07-01), None
patent: 05150244 (1993-06-01), None
patent: 11242217 (1999-09-01), None
Choi Do Hyun
Lee Kyung Ha
Rim Seung Moo
Hyundai Display Technology Inc.
Ladas & Parry
Schechter Andrew
Ton Toan
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