Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2000-12-29
2003-02-11
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S147000, C349S139000
Reexamination Certificate
active
06519014
ABSTRACT:
CROSS REFERENCE
This application claims the benefit of Korean Patent Application Nos. 1999-67855 filed on Dec. 31, 1999 under 35 U.S.C. §119, the entirety 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. 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 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 a sufficient power to the backlight of such a device. However, this has a problem that the battery can not be used for a lengthy period of 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 typical reflective LCD device in cross section. As shown in
FIG. 2
, the reflective LCD device includes upper and lower substrates
8
and
10
with a liquid crystal layer
12
interposed. The upper substrate
8
includes color filter layers
4
a,
4
b
and
4
c
(e.g., red, green, and blue) and a common electrode
6
. The lower substrate
10
includes a switching element (not shown) and a reflective electrode
2
.
Ambient light
100
passes through the upper substrate
8
and the liquid crystal layer
12
and is reflected on the reflective electrode
2
. When electrical signals are applied to the reflective electrode
2
by the switching element, phase of the liquid crystal layer
12
varies. Then, reflected light is colored by the color filter layers
4
a,
4
b
and
4
c
and displayed in the form of images.
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. 3
shows a conventional transflective LCD device. As shown in
FIG. 3
, the conventional transflective LCD device includes upper and lower substrates
22
and
18
with a liquid crystal layer
20
interposed. The upper substrate
22
includes a color filter
104
, and the lower substrate
18
, referred to as an array substrate, includes a switching element (not shown), a pixel electrode
14
and a reflective electrode
2
. The reflective electrode
2
is made of an opaque conductive material having a good reflectance and light transmitting holes “A” are formed therein. The transflective LCD device further includes a backlight device
16
. The light transmitting holes “A” serve to transmit light
112
from the backlight device
16
,
The transflective LCD device in
FIG. 3
is operable in transmissive and reflective modes. First, in reflective mode, the incident light
110
from the upper substrate
22
is reflected on the reflective electrode
2
and directed toward the upper substrate
22
. At this time, when electrical signals are applied to the reflective electrode
2
by the switching element (not shown), phase of the liquid crystal layer
20
varies and thus the reflected light is colored by the color filter
104
and displayed in the form of images.
Further, in transmissive mode, light
112
generated from the backlight device
16
passes trough portions of the pixel electrode
14
corresponding to the transmitting holes “A”. When the electrical signals are applied to the pixel electrode
14
by the switching element (not shown), phase of the liquid crystal layer
20
varies. Thus, the light
112
passing through the liquid crystal layer
20
is colored by the color filter
104
and displayed in the form of images.
Detailed explanation of the transflective LCD device and the fabrication method will be provided with reference to
FIGS. 4
,
5
A and
5
B.
FIG. 4
is a partially enlarged plan view of an array substrate for a transflective LCD device according to a conventions art. As shown in
FIG. 4
, the array substrate has gate and data lines
25
and
27
crossing each other. A pixel region “p” is defined by the crossing. As a pixel electrode
19
, there are a transparent electrode
19
a
and a reflective electrode
19
b
in the pixel region “p”. The reflective electrode
19
b
has a reflective region “C” and a transmitting hole “A” as a transmitting region through which light from the backlight is transmitted. The pixel electrode
19
receives a signal from a TFT “T” having gate, source and drain electrodes
61
,
63
and
65
. The gate and source electrodes
61
and
63
are respectively extended from the gate and data lines
25
and
27
. The drain electrode
65
is connected to the transparent and reflective electrodes
19
a
and
19
b
through first and second drain contact holes
65
and
71
.
A fabrication method will be explained with reference to
FIGS. 5A and 5B
which are cross sectional views taken lines IV—IV and V—V of
FIG. 4
, respectively. First, on a substrate
59
a gate line
25
having a gate electrode
61
is formed. On the gate line
61
, a first insulating layer
60
is formed using an organic material such as acetyl or benzocyclobutene (BCB) or an inorganic material such as silicon nitride or silicon dioxide. On the first insulating layer
60
over the gate electrode
61
sequentially formed are an active layer
62
, source and drain electrodes
63
and
65
, and a second insulating layer
64
having the first drain contact hole
67
. On the second insulating layer
64
formed is the transparent electrode
19
a
contacting the drain electrode
65
through the first drain contact hole
67
. The transparent electrode
19
a
has a hole corresponding to the second drain contact hole
71
that will be formed later.
Next, on the transparent electrode
19
a
an insulating material is deposited and patterned to form the protection layer
69
having the drain contact hole
71
exposing the drain electrode
65
. On the protection layer
69
is formed the reflective electrode
19
b
having the transmitting hole “A” at the pixel region. The reflective electrode
19
b
contacts the drain electrode
65
via the second drain contact hole
71
.
Meanwhile, since there are two electrodes
19
a
and
19
b
contacting the drain electrode
65
for pixel electrode
19
in this structure, the electric field applied to the liquid crystal can be deflected due to the difference of locations of the two electrodes
19
a
and
19
b,
leading to lower the driving efficiency of the liquid crystal. Further, since the second drain contact hole is deep enough to result in a crack of the protection layer
69
or the reflective electrode at the corresponding position, the resistance of the reflective electrode can increase than expected, and particles
Akkapeddi P. R.
Birch & Stewart Kolasch & Birch, LLP
LG. Philips LCD Co. Ltd.
Sikes William L.
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