Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-11-22
2003-10-21
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S143000
Reexamination Certificate
active
06636286
ABSTRACT:
CROSS REFERENCE
This application claims the benefit of Korean Patent Application Nos. 1999-552862 filed on Nov. 26, 1999 under 35 U.S.C. §119, the entirety of each of which is hereby incorporated by reference.
BACKGROUND
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a transflective LCD device.
2. Description of Related Art
In general, liquid crystal displays are divided into transmissive LCD devices and reflective LCD devices according to whether the display uses an internal or external light source.
A typical transmissive LCD device includes a liquid crystal panel and a back light device. The liquid crystal panel includes upper and lower substrates with a liquid crystal layer interposed therebetween. The upper substrate includes a color filter, and the lower substrate includes thin film transistors (TFTs) as switching elements. An upper polarizer is arranged on the liquid crystal panel, and a lower polarizer is arranged between the liquid crystal panel and the backlight 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 shown 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 a sufficient power to the backlight of such a device. However, this has 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 to the transmissive LCD device.
FIG. 2
shows a sub-pixel of a typical reflective LCD device
100
in plane. A plurality of gate lines, including (N−1)th gate line
6
and Nth gate line
8
, are spaced apart from each other, and a plurality of data lines, including Nth data line
2
and (N+1)th gate line
4
, are arranged perpendicular to the gate lines. In an area defined by the gate and date lines, a reflective electrode
10
is positioned. The gate and data lines and the reflective electrodes make a shape of an array matrix.
In the Nth gate line
8
, near a cross point of the Nth gate and data lines
8
and
2
, a gate electrode
18
is positioned, and a source electrode
12
is positioned in the Nth data line
2
. The source electrode
12
overlaps a portion of the gate electrode
18
. Spaced apart from the source electrode
12
, a drain electrode
14
is positioned and overlaps a portion of the gate electrode
18
. The drain electrode
14
electrically contacts a reflective electrode
10
via a drain contact hole
16
that is formed on the drain electrode
14
. Conventionally, the reflective electrode
10
is a metal that has a superior reflexibility.
With reference to
FIG. 3
, a cross-sectional structure of the conventional reflective TFT-LCD device shown in
FIG. 2
is described in detail.
On a substrate
1
, the gate electrode
18
and the gate insulating layer
20
are positioned sequentially. The gate insulating layer
20
covers the gate electrode
18
. On the gate insulating layer
20
, a semiconductor layer
22
is positioned, and the source and drain electrodes
12
and
14
that contact the semiconductor layer
22
are positioned.
A passivation layer
24
is positioned over the overall surface of the substrate
1
. On the passivation layer
24
, the drain contact hole
16
is positioned to expose a portion of the drain electrode
14
. The reflective electrode
10
is positioned on the passivation layer
24
and contacts the drain electrode
14
via the drain contact hole
16
.
However, the reflective LCD device is affected by its surroundings. For example, the brightness of ambient light in an office differs largely from that outdoors. Even in the same location, the brightness of ambient light depends on the time of day (e.g., noon or dusk).
In order to overcome the problems described above, a transflective LCD device has been developed.
FIG. 4
shows a conventional transflective LCD device. As shown in
FIG. 4
, the transflective LCD device includes gate line
50
arranged in a transverse direction, data line
60
arranged in a longitudinal direction perpendicular to the gate line
50
, a thin film transistor “T” (TFT) located near the cross points of the gate and data line
50
and
60
. Each of the TFTs “T” includes gate, source, and drain electrodes
52
,
62
, and
64
. The gate and source electrodes
52
and
62
are extended from the gate and data line
50
and
60
, respectively. The transflective LCD device further includes a reflective electrode
68
and a pixel electrode
70
. The pixel electrode
70
is electrically connected with the drain electrode
64
via a first contact hole
66
, and the reflective electrode
68
is electrically connected with the pixel electrode
70
via a second contact hole
67
. The reflective electrode
68
is made of an opaque conductive material and preferably the same material as the gate electrode
52
, and the pixel electrode
70
is made of a transparent conductive material such as indium tin oxide (ITO). The reflective electrode
68
has a light transmitting hole
72
for transmitting light from a backlight device (see
102
in FIG.
5
). The light transmitting hole
72
may have a circular or a rectangular shape and thus is not limited in its shape. The pixel electrode
70
should have a sufficient area to cover the light transmitting hole
72
.
As shown in
FIG. 5
, the conventional transflective LCD device includes upper and lower substrates
106
and
108
with a liquid crystal layer
100
interposed therebetween. The upper substrate
106
includes a color filter
104
, and the lower substrate
108
includes a switching element (not shown), a pixel electrode
70
and a reflective electrode
68
. A protection film
74
is interposed between the pixel and the reflective electrodes
70
and
68
. The reflective electrode
68
is made of an opaque conductive material having a good reflectance, and a light transmitting hole
72
is formed therein. The transflective LCD device further includes a backlight device
102
. The light transmitting hole
72
serves to transmit light
114
from the backlight device
102
.
The transflective LCD device in
FIG. 5
is operable in transmissive and reflective modes. First, in reflective mode, the incident light
110
from the upper substrate
106
is reflected on the reflective electrode
68
and directed toward the upper substrate
106
. At this time, when electrical signals are applied to the reflective electrode
68
by the switching element (not shown), the phase of the liquid crystal layer
100
varies and thus the reflected light
120
is colored by the color filter
104
and displayed in the form of images.
Further, in transmissive mode, light
114
generated from the backlight device
102
passes through portions of the pixel electrode
70
corresponding to the transmitting hole
72
. When the electrical signals are applied to the pixel electrode
70
by the switching element (not shown), phase of the liquid crystal layer
114
varies. Thus, the light
114
passing through the liquid crystal layer
100
is colored by the color filter
104
such that images are displayed.
As described above, since the transflective LCD device has both transmissive and reflective modes, the transflective LCD device can be used without regard to the time of day (e.g., noon or dusk). It also has the advantage that it can be used for a long time by consuming low power. However, since the reflective electrode has a the transmitting hole
72
, the conventional transfl
Kim Robert H.
LG.Philips LCD Co. , Ltd.
Schechter Andrew
LandOfFree
Transflective liquid crystal display device having... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transflective liquid crystal display device having..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transflective liquid crystal display device having... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3135759