Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-06-20
2004-05-11
Ngo, Julie-Huyen L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S043000, C349S046000, C349S113000
Reexamination Certificate
active
06734935
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2001-39638, filed on Jul. 4, 2001 in Korea, 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 (LCD) device and more particularly, to an array panel for a transflective liquid crystal display device.
2. Discussion of the Related Art
In general, the LCD device includes two substrates, which are spaced apart and facing each other, and a liquid crystal layer interposed between the two substrates. Each of the substrates includes an electrode and the electrodes of each substrate are facing each other, also. Voltage is applied to each electrode and an electric field is induced between the electrodes. An alignment of the liquid crystal molecule is changed by the intensity of the electric field, and the LCD device displays a picture by transmissivity of the light varying according to the arrangement of the liquid crystal molecules.
Because the liquid crystal display device is not luminescent, it needs an additional light source in order to display images, and the liquid crystal display device is categorized into a transmissive type and a reflective type depending on the kind of light source.
In the transmissive type, a back light behind a liquid crystal panel is used as a light source. Light incident from the back light penetrates the liquid crystal panel, and the amount of the transmitted light is controlled according to the alignment of the liquid crystal molecules. Here, the substrates must be transparent and the electrode of each substrate must also be formed of transparent conductive material. As the transmissive liquid crystal display device uses the back light as a light source, it can display a bright image in dark surroundings. By the way, because an amount of the transmitted light is very small for the light incident from the back light, the brightness of the back light should be increased in order to increase the brightness of the LCD device. Consequently, the transmissive liquid crystal display device has high power consumption due to the back light.
On the other hand, in the reflective type LCD device, sunlight or artificial light is used as a light source of the LCD device. The light incident from the outside is reflected at a reflective plate of the LCD device according to the arrangement of the liquid crystal molecules. Since there is no back light, the reflective type LCD device has much lower power consumption than the transmissive type LCD device. However, the reflective type LCD device cannot be used in dark places because it depends on an external light source.
Therefore, a transflective LCD device, which can be used both in a transmissive mode and in a reflective mode, has been recently proposed. A conventional transflective LCD device will be described hereinafter more in detail.
FIG. 1
is a cross-sectional view of a conventional transflective LCD device. In
FIG. 1
, the conventional transflective LCD device has a lower substrate
10
and an upper substrate
30
, and the substrates
10
and
30
are spaced apart from and facing each other.
A pixel electrode
20
is formed on the inner surface of the lower substrate
10
and connected to the thin film transistor (not shown) formed on the inner surface of the lower substrate
10
. The pixel electrode
20
includes a transmissive electrode
21
and a reflective electrode
22
. The reflective electrode
22
has a hole in which the transmissive electrode
21
is located. The transmissive electrode
21
is formed of a transparent conductive material such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO), which has high transmittance. The reflective electrode
22
is formed of an opaque conductive material such as aluminum (Al), which has high reflectance and low resistivity.
Next, a color filter
40
, which corresponds to the pixel electrode
20
, is formed on the inner surface of the upper substrate
30
and a common electrode
50
is formed on the color filter
40
. The common electrode
50
is also made of the transparent conductive material.
A liquid crystal layer
60
is disposed between the lower and upper substrates
10
and
30
, and molecules of the liquid crystal layer
60
are arranged horizontally with respect to the substrates
10
and
30
.
On the outer surfaces of the substrates
10
and
30
, a first retardation film
71
and a second retardation film
72
are arranged, respectively. The first and second retardation films
71
and
72
change the polarized state of light. In case of the first and second retardation films
71
and
72
having a phase difference of &lgr;/4 (&lgr;=550 nm), an incident circular polarized light changes into linear polarized light, and an incident linear polarized light changes into circular polarized light.
A first polarizer
81
and a second polarizer
82
are arranged on the outer surface of the first and second retardation films
71
and
72
. The second polarizer
82
is an analyzer, and the transmission axis of the second polarizer
82
has an angle of 90 degrees with the transmission axis of the first polarizer
81
.
Next, a back light
90
is located under the outside of the first polarizer
81
. The back light
90
is used as a light source of a tranmissive mode of the transflective LCD device.
This transflective LCD device is a normally white mode and in such case, white light is emitted when voltage is not applied. By the way, the transflective LCD device is planned on the basis of the reflective mode. Accordingly, transmittance of the transmissive mode becomes only 50% of the transmittance of the reflective mode when the voltage is not applied, and thus gray light is emitted in the transmissive mode.
FIG. 2
illustrates the transflective LCD device to solve the above problem. In
FIG. 2
, the transflective LCD device is divided into a transmissive region “A” and a reflective region “B”.
The transflective LCD device has a lower substrate
110
and an upper substrate
160
facing apart from each other. A first passivation layer
120
is formed on the inner surface of the lower substrate
110
, and the first passivation layer
120
has a first trasmissive hole
122
in the transmissive region “A”. A transmissive electrode
130
of a transparent conductive material is formed on the first passivation layer
120
. Next, a second passivation layer
140
is formed on the transmissive electrode
130
, and a reflective electrode
150
is formed on the second passivation layer
140
. The reflective electrode
150
has a second transmissive hole
152
exposing the transmissive electrode
130
on the first transmissive hole
122
. On the other hand, a thin film transistor (not shown) is formed on the inner surface of the lower substrate
110
, and the thin film transistor is connected electrically to not only the transmissive electrode
130
but also the reflective electrode
150
.
A color filter
161
is formed on the inner surface of the upper substrate
160
and a common electrode
162
is formed on the color filter
161
.
Next, retardation films
171
and
172
are arranged on the outer surface of the lower and upper substrates
110
and
160
, respectively. Polarizers
181
and
182
are arranged on the outer surface of the respective retardation film
171
and
172
. A back light
190
is located under the lower polarizer
181
.
A liquid crystal layer
200
is disposed between the reflective electrode
150
and the common electrode
162
. The liquid crystal molecules of the liquid crystal layer
200
are arranged horizontally with respect to the substrates
110
and
160
. The liquid crystal layer
200
has a positive permittivity anisotropy value, so the liquid crystal molecules are arranged parallel to a direction of the electric field induced between the reflective electrode
150
and the common electrode
162
when voltage is applied to the electrodes
130
,
150
and
162
.
A phase difference of the liquid crystal layer depends on the re
Cho Heung-Lyul
Ha Kyoung-Su
Kim Dong-Guk
McKenna Long & Aldridge LLP
Ngo Julie-Huyen L.
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