Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-09-28
2003-09-16
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S114000
Reexamination Certificate
active
06621541
ABSTRACT:
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
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 through 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.
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 the transmitting holes “A”, the conventional transflective LCD device has a very low light utilizing efficiency compared to either the reflective LCD device or the transmissive LCD device alone.
FIG. 4A
shows a conventional reflective electrophoretic display. As shown in
FIG. 4A
, the reflective electrophoretic display
300
includes a front panel
24
having a first conducting electrode
25
a
and a first substrate
2
a
, and a rear panel
26
having a second conducting electrode
25
b
and a second substrate
2
b
. The display
300
also includes a suspension of charged pigment particles
30
colloidally dispersed in a dyed liquid
28
interposed between the front and rear panels
24
and
26
.
The reflective electrophoretic display
300
operates as follows. As shown in
FIG. 4B
, when a d.c. voltage is applied to the first and second conducting electrodes
25
a
and
25
b
, charged pigment particles
30
contained in a dyed liquid
28
move and are packed on the first conducting electrode
25
a
having the same polarity so that the pigment particle layer
30
a
is formed. If polarity of the d.c. voltage is changed, the charged pigment particles
30
are packed (not shown) on the second conducting electrode
25
b
. When the pigment is packed on the first conducting electrode
25
a
, the color of the pigment will be seen by the observer with ambient light. When the pigment is packed on the second conducting electrode
25
b
, the ambient room light is absorbed and scattered by the dyed liquid
28
and the color of the dye is observed.
However, such a display utilizing electrophoresis has a problem that its response speed is slow, and it requires a high operating voltage. Further, pixelization is technically difficult. Also, the performance of the electrophoretic display above is far inferior to the LCD device.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a transflective liquid crystal display device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
In accordance with the purpose of the invention, as embodied and broadly described, in one aspect the invention includes a transflective liquid crystal display device, including: a liquid crystal panel including a first substrate having a color filter, a second substrate having a switching element and a pixel electrode, and a liquid crystal layer interposed between the first and second substrates; an electrophoretic display arranged under the liquid crystal panel, the electrophoretic display including a first panel having a first conducting electrode which defines a transmitting region for transmitting light at a location corresponding to the pixel electrode, a second panel having a second conducting electrode, and a transparent liquid interposed between the first and second panels and having charged pigment particles; and a backlight device arranged under the electrophoretic display.
In another aspect, t
Birch & Stewart Kolasch & Birch, LLP
Dudek James
LG. Philips LCD Co. Ltd.
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