Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2000-12-21
2003-03-11
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S114000, C349S110000, C349S111000, C349S113000
Reexamination Certificate
active
06532045
ABSTRACT:
CROSS REFERENCE
This application claims the benefit of Korean Patent Application No.
1999 -63250
, filed on Dec. 28, 1999, under 35 U.S.C. §119, the entirety of 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 a transflective LCD device and a method of manufacturing the same.
2. Description of Related Art
Until now, the cathode-ray tube (CRT) has been developed for and is mainly used for the display systems. However, the flat panel display is beginning to make its appearance due to the requirement of the small depth dimensions and the desirability of low weight and low voltage power supply. At this point, the thin film transistor-liquid crystal display (TFT-LCD) having a high resolution and small depth dimension has been developed.
In the operating principles of the TFT-LCD, when the pixel is turned ON by the switching elements, the pixel transmits the light generated from the backlight device. The switching elements are generally an amorphous silicon thin film transistor (a-Si:H TFT) which has the semiconductor layer because the amorphous silicon TFT can be formed on a low cost glass substrate at low temperature.
In general, the TFT-LCD produces the image using the light from the back light device that is positioned under the TFT-LCD panel. However, the TFT-LCD only employs 3~8% of the incident light generated from the backlight device, i.e., inefficient optical modulation.
Referring to the attached drawings, an array substrate of an LCD device that is manufactured by a conventional method will now be explained in some detail.
FIG. 1
is a graph illustrating a transmittance respectively measured after light passes through each layer of a conventional liquid crystal display device.
The two polarizers have a transmittance of 45% and, the two substrates have a transmittance of 94%. The TFT array and the pixel electrode have a transmittance of 65%, and the color filter has a transmittance of 27%. Therefore, the typical transmissive LCD device has a transmittance of about 7.4% as seen in
FIG. 1
, which shows a transmittance (in brightness %) after light passes through each layer of the device. For this reason, the transmissive LCD device requires a high initial brightness, and thus electric power consumption by the backlight device increases. A relatively heavy battery is needed to supply sufficient power to the backlight of such a device. Moreover, there still exists a problem that the battery can not be used for a long time.
In order to overcome the problem described above, the reflective LCD has been developed. Since the reflective LCD device uses ambient light, it is light and easy to carry. Also, the reflective LCD device is superior in aperture ratio compared to the transmissive LCD device.
FIG. 2
is a plan view illustrating a typical reflective LCD device. As shown in
FIG. 2
, the reflective LCD device
100
includes gate lines
6
and
8
arranged in a transverse direction, data lines
2
and
4
arranged in a longitudinal direction perpendicular to the gate lines
6
and
8
, and thin film transistors (TFTs), for example, the thin film transistor “S” near a cross point of the gate line
8
and the data line
2
. Each of the TFTs “S” has a gate electrode
18
, a source electrode
12
and a drain electrode
14
. The source electrode
12
extends from the data line
2
, and the gate electrode
18
extends from the gate line
8
. The reflective LCD device
100
further includes reflective electrodes
10
. The reflective electrode
10
is electrically connected with the drain electrode
14
through a contact hole
16
and is made of a metal having a good reflectance.
FIG. 3
is a cross sectional view taken along the line III—III of FIG.
2
. As shown in
FIG. 3
, the gate electrode
18
is formed on the substrate
1
, and a gate insulating layer
20
is formed on the exposed surface of the substrate
1
while covering the gate electrode
18
. A semiconductor layer
22
as an active area of the TFT “S” (see
FIG. 2
) is formed over the gate electrode
18
. The source and drain electrodes
12
and
14
are spaced apart from each other. The source electrode
12
overlaps one end portion of the semiconductor layer
22
, and the drain electrode
14
overlaps the other end portion of the semiconductor layer
22
. A passivation film
24
is formed over the whole surface of the substrate
1
while covering the TFT “S”. The passivation film
24
has the contact hole
16
on the predetermined portion of the drain electrode
14
. The reflective electrode
10
is formed on the passivation film
24
and is electrically connected with the drain electrode
14
through the contact hole
16
.
As mentioned above, since the reflective LCD device uses ambient light, a battery is not necessary. By the way, the reflective LCD device has a problem in that it is affected by its surroundings. For example, the brightness of indoors-ambient light differs largely from that of outdoors. Also, even in the same location, the brightness of ambient light depends on the time of day (e.g., noon or dusk). Therefore, the reflective LCD device cannot be used at night without ambient light.
For the foregoing reasons, there is a need for a transflective LCD device that can be used during the day as well as at night.
FIG. 4
is a plan view illustrating an array substrate of a transflective liquid crystal display (LCD) device according to a conventional art. As shown in
FIG. 4
, the array substrate includes a gate line
50
arranged in a transverse direction, data line
60
arranged in a longitudinal direction perpendicular to the gate line
50
, and a thin film transistor (TFT) arranged near the cross portion of the gate and data lines
50
and
60
. The TFT has a gate electrode
52
, a source electrode
62
and a drain electrode
64
. The gate electrode
52
extends from the gate line
50
, and the source electrode
62
extends from the data line
60
. The drain electrode
64
is spaced apart from the source electrode
62
. And the source electrode
62
overlaps one end portion of the gate electrode
52
, and the drain electrode
64
overlaps the other end portion of the gate electrode
52
. The array substrate further includes a reflective electrode
68
and a pixel electrode
70
, which are formed on a region defined by the gate and data lines
50
and
60
. The reflective electrode
68
and the pixel electrode
70
are electrically connected with the drain electrode
64
through contact hole
69
and
66
(see FIG.
5
C). The reflective electrode
68
is made of an opaque conductive metal, and the pixel electrode
70
is made of a transparent conductive material. The reflective electrode
68
has a light transmitting hole
72
formed on a central portion thereof. The light transmitting hole
72
serves to transmit light and has a substantially rectangular shape. The pixel electrode
70
has a sufficient size to cover the light transmitting hole
72
. In other words, the pixel electrode
70
covers the light transmitting hole
72
.
FIGS. 5A
to
5
D are cross sectional views taken along the line V—V of
FIG. 4
, illustrating a process of manufacturing the array substrate of the transflective LCD device according to the conventional art.
First, as shown in
FIG. 5A
, a first metal layer is deposited on a substrate
1
and patterned into the gate electrode
52
. The first metal layer is made of a metal having a high corrosion resistance such as Chrome or Tungsten or having a low resistance such as Aluminum alloy.
Then, as shown in
FIG. 5B
, a gate insulating layer
80
, a semiconductor layer
82
and the source and drain electrodes
62
and
64
are sequentially formed. The gate insulating layer
80
is formed on the exposed surface of the substrate
1
while covering the gate electrode
52
. The semiconductor layer
82
is formed on the gate insulating layer
80
and over the gate electrode
52
. The source electrode
62
overlaps one end portion of the semiconduct
Chung Jae-Young
Park Sang-Chol
Duong Thoi V.
Kim Robert H.
LG. Philips LCD Co. Ltd.
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