Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-04-17
2003-08-26
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S113000, C349S141000
Reexamination Certificate
active
06611306
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-20117, filed on Apr. 17, 2000, 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 that has a high brightness.
2. Description of Related Art
Until now, the cathode-ray tube (CRT) has been developed for and is used mainly for the display systems. However, the flat panel display is beginning to make its appearance due to the requirements of small depth dimensions, undesirably low weight and low voltage power supply. At present, the thin film transistor-liquid crystal display (TFT-LCD) with high resolution and small depth dimension has been developed.
During operation of the TFT-LCD, when the pixel is turned ON by the corresponding switching elements, the pixel transmits light generated from a backlight device. The switching elements are generally amorphous silicon thin film transistors (a-Si:H TFTs) which use an amorphous silicon layer. Advantageously, the amorphous silicon TFTs can be formed on low cost glass substrates using low temperature processing.
In general, the TFT-LCD transmits an image using light from the backlight 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., the inefficient optical modulation.
Referring to
FIGS. 1-5B
, a TFT-LCD device that is manufactured by a conventional method will now be explained in some detail.
FIG. 1
is a graph illustrating a light 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 TFT-LCD device has a transmittance of about 7.4% as seen in
FIG. 1
, which shows a transmittance after light passes through each layer of the device. For this reason, the transmissive TFT-LCD device requires a high, initial brightness, thereby increasing electric power consumption of the backlight device. A relatively heavy battery is needed to supply a sufficient power to the backlight of such a device. Moreover, there still exists a problem that the battery cannot be used for a long time.
In order to overcome these problems, a reflective TFT-LCD has been developed. Since the reflective TFT-LCD device uses ambient light, it is light and easy to carry. Also, the reflective TFT-LCD device is superior in aperture ratio as compared to a transmissive TFT-LCD device. Namely, since the reflective TFT-LCD substitutes an opaque reflective electrode for a transparent electrode material in the pixel of the conventional transmissive TFT-LCD, it reflects the ambient light.
As described above, since the reflective TFT-LCD device uses ambient light other than an internal light source such as a backlight device, battery life can be increased resulting in longer use times. In other words, the reflective TFT-LCD device is driven using light reflected from the reflective electrode. Thus, only the drive circuitry that drives the liquid crystal uses the battery power in the reflective TFT-LCD device.
Additionally, the reflective TFT-LCD device has a problem that it is affected by its surroundings. For example, the brightness of indoors-ambient light differs largely from that of outdoors-ambient light. 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 TFT-LCD device cannot be used at night without ambient light.
Accordingly, there is a need for a transflective TFT-LCD device that can be used during daytime hours as well as nighttime because the transflective LCD device can be changed to either a transmissive mode or a reflective mode depending on the desired condition of operation.
FIG. 2
is a schematic cross-sectional view illustrating one pixel of the transflective TFT-LCD device according to the conventional art. As shown, the transflective TFT-LCD device
51
includes a liquid crystal panel and a backlight device
70
. The liquid crystal display panel includes lower and upper substrates
50
and
60
and an interposed liquid crystal layer
80
. The upper and lower substrates
60
and
50
are called a color filter substrate and an array substrate, respectively.
The upper substrate
60
has color filters
61
. The lower substrate
50
serves as the array substrate and includes TFTs (not shown), and transmissive and reflective electrodes
54
and
52
serve as a pixel electrode. The reflective electrode
52
surrounds the transmissive electrode
54
or has a light transmitting hole
53
having a dimension “&Dgr;L”. The reflective electrode
52
includes a conductive material such as chrome (Cr), aluminum (Al) or tantalum (Ta), which has a high optical reflectivity, and therefor reflects the ambient light
74
. The transmissive electrode
54
, formed in the light transmitting hole
53
, transmits the light
72
emitted from the backlight device
70
.
The transflective LCD device
51
is operated as follows. First, in the reflective mode, the incident light
74
from the outside is reflected from the reflective electrode
52
and is directed toward the upper substrate
60
. At this time, when the electrical signals are applied to the reflective electrode
52
by the switching elements (not shown), the arrangement of the liquid crystal layer
80
varies, and thus, the reflected light of the incident light
74
is colored by the color filter
61
and is displayed as colored light. Second, in the transmissive mode, light
72
emitted from the backlight device
70
passes through the transmissive electrode
54
(or transmitting hole
53
). At this time, when the electrical signals are applied to the transmissive electrode
54
by the switching elements (not shown), arrangement of the liquid crystal layer
80
varies. Thus, the light
72
passing through the liquid crystal layer
80
is colored by the color filter
61
and displayed in the form of images with other colored lights.
FIG. 3
is a cross-sectional view of the conventional transflective LCD device. In
FIG. 3
, the color filter is not depicted because it does not affect the polarization state of the light. As shown, the conventional transflective LCD device
110
includes a first substrate
106
(an array substrate) and a second substrate
204
(a color filter substrate). A liquid crystal layer
300
that affects the polarization state of the light according to the applied voltages is interposed between the first substrate
106
and the second substrate
204
.
On the surface of the first substrate
106
that faces the second substrate
204
, a TFT (not shown), a transparent conductive electrode
150
(i.e., a pixel electrode) and a reflective electrode
108
(i.e., a pixel electrode) are disposed. Lower polarizer
102
is disposed on the other surface of the first substrate
106
. Moreover, a lower retardation film (quarter wave plate; QWP)
104
having a phase difference &lgr;/4 is positioned between the first substrate
106
and the lower polarizer
102
. A backlight device
101
is adjacent to the lower polarizer
102
. The lower polarizer
102
, the lower retardation film
104
, the first substrate
106
, the transparent conductive electrode
150
, and the reflective electrode
108
are all together referred to as a lower substrate
100
.
On one surface of the second substrate
204
is a second retardation film, i.e., Quarter Wave Plate (&lgr;/4 plate); referred to hereinafter as a second QWP
206
. On the second QWP
206
is an upper linear polarizer
208
. A transparent conductive common electrode
202
is on the other surface of the second substrate
204
facing the lower substrate
100
. The common electrode
202
, the second
Kim Robert H.
LG. Philips LCD Co. Ltd.
Morgan & Lewis & Bockius, LLP
Rude Timothy L
LandOfFree
Transflective liquid crystal display device with dual liquid... 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 with dual liquid..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transflective liquid crystal display device with dual liquid... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3086345