Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-08-21
2003-10-28
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S122000, C349S110000
Reexamination Certificate
active
06639639
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-48236, filed on Aug. 21, 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 reflective and transflective LCD devices having black resin.
2. Description of Related Art
Until now, the cathode-ray tube (CRT) has been developed and mainly used for display systems. However, flat panel displays are beginning to make an appearance because of their small depth dimensions, desirably low weight, and low voltage power supply requirements. Presently, thin film transistor-liquid crystal displays (TFT-LCDs) with high resolution and small depth dimension are being developed.
During operation of the TFT-LCD, a pixel is turned ON by switching elements to transmit light generated from a backlight device. The switching elements are generally amorphous silicon thin film transistors (a-Si:H TFTs) that use an amorphous silicon layer. Advantageously, the amorphous silicon TFTs can be formed on low cost glass substrates using low temperature processing techniques.
In general, the TFT-LCD transmits image data using light emitted from the backlight device that is positioned under a TFT-LCD panel. However, the TFT-LCD only employs 3~8% of the incident light generated from the backlight device, thereby providing inefficient optical modulation. In the TFT-LCD device, two polarizers will typically have a transmittance of 45% and two corresponding substrates will typically have a transmittance of 94%. The TFT array and the pixel electrode may have a transmittance of 65% and the color filter may have a transmittance of 27%. Therefore, the typical transmissive TFT-LCD device has a relative transmittance of about 7.4% as shown in FIG.
1
. Additionally,
FIG. 1
also shows the relative transmittance after light passes through each layer of the device. For this reason, the transmissive TFT-LCD device requires a light source having a relatively high initial brightness. However, such a high initial brightness increases electric power consumption requirements of the backlight device. Accordingly, a relatively heavy battery is needed to supply sufficient power to the backlight device. Moreover, use of the battery source will limit the time in which the TFT-LCD can properly operate.
In order to overcome these problems, a reflective TFT-LCD has been developed. Since the reflective TFT-LCD device uses ambient light as a light source, the device is light and portable. Additionally, the reflective TFT-LCD device has a superior 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, the opaque reflective electrode reflects ambient light. Accordingly, since the reflective TFT-LCD device uses ambient light rather than an internal light source, battery life of the reflective TFT-LCD can be increased resulting in a longer period of use. In other words, the reflective TFT-LCD device is driven using light reflected from the reflective electrode, thereby only drive circuitry that drives the liquid crystal uses the battery source in the reflective TFT-LCD device.
FIG. 2
is a schematic cross-sectional view of a conventional reflective liquid crystal display device. In
FIG. 2
, the reflective LCD device
20
comprises an upper substrate
2
, a lower substrate
4
, and a liquid crystal layer
3
interposed therebetween. On a first surface of the upper substrate
2
that opposes the lower substrate
4
, a black matrix
6
isolates color filters
8
(Red, Green and Blue) that are disposed on the first surface of the upper substrate
2
. The color filters
8
and the black matrix
6
are disposed on a similar plane, and a transparent common electrode
10
is disposed on the color filters
8
and black matrix
6
.
A gate insulation layer
18
is disposed on a first surface of the lower substrate
4
that opposes the first surface of the upper substrate
2
. A passivation layer
14
is disposed on the gate insulation layer
18
, and data lines
16
that transmit data signals to the TFT (not shown) are disposed between the gate insulation layer
18
and the passivation layer
14
and on both sides of a pixel region. A reflective electrode
12
is disposed on the passivation layer
14
and, in combination with the transparent electrode
10
, controls orientation of liquid crystal molecules
9
by application of an electric field. The reflective electrode
12
reflects ambient light to display image data and functions as a pixel electrode. Furthermore, since the reflective LCD device
20
displays image data using the ambient light, lateral side edges of the reflective electrode
12
overlap portions of the data lines
16
, thereby increasing aperture ratio. The reflective electrode
12
is formed of an opaque metallic material that has superior light reflectance, while the passivation layer
14
is formed of an insulating material that has a low dielectric constant of about 3 (&egr;≈3), such as benzocyclobutene (BCB) or acryl-based resin, for example. Accordingly, since the passivation layer is disposed between the reflective electrode
12
and the data lines
16
, electrical interference, i.e., cross talk, is prevented. Here, a thickness of the passivation layer
14
is about 1.5 micrometers (&mgr;m).
In
FIG. 2
, an overlap area “A” represents an area of the pixel electrode
12
that overlaps the data line
16
. Since the data line
16
is shielded from incident light by this overlap area “A” of the pixel electrode
12
, a substantial portion of the black matrix
6
corresponding to the overlap area “A” can be removed. However, if the portion of the black matrix
6
corresponding to the overlap area “A” is removed, a width of the black matrix
6
is narrowed, thereby creating misalignment problems during manufacturing processes. For example, the misalignment of the red, green and blue color filters
8
is created due to a small aligning margin of the black matrix
6
, and the misalignment of the upper and lower substrates is created when attaching the upper substrate
2
to the lower substrate
4
. The width of the overlap area “A” is about 2 &mgr;m, and a width of the black matrix is ideally about 4 &mgr;m. However, in practice the ideal width of the black matrix is difficult to obtain because of the above-mentioned problems. Accordingly, a width of more than 4 &mgr;m needs to be maintained for the black matrix so that the overlap area “A” is covered by the black matrix. Thus, increasing the aperture ratio is difficult.
Meanwhile, the reflective TFT-LCD device can be adversely affected by its surroundings. For example, the brightness of indoor ambient light differs greatly from the brightness of outdoor ambient light. In addition, the brightness of the outdoor ambient light is dependent upon the time of day (i.e., noon or dusk) such that the reflective TFT-LCD device cannot be used at night without sufficient ambient light. Accordingly, there is a need for a transflective TFT-LCD device that can be used during daylight hours, as well as nighttime, since the transflective LCD device can be changed to either a transmissive mode or a reflective mode depending on the desired condition of operation.
FIG. 3
is a schematic cross-sectional view of a pixel area of a conventional transflective liquid crystal display device. In
FIG. 3
, the transflective TFT-LCD device includes a liquid crystal panel
45
and a backlight device
44
. The liquid crystal display panel
45
includes an upper substrate
22
, a lower substrate
24
and a liquid crystal layer
31
interposed therebetween. The upper substrate
22
and the lower substrate
24
are commonly referred to as a color filter substrate and an array substrate, respectively. The upper substrate
22
includes a black matrix
26
and color filters
28
on a su
Baek Heum-Il
Ha Kyoung-Su
Kim Dong-Guk
Kim Yong-Beom
Chung David
LG. Philips LCD Co. Ltd.
Morgan & Lewis & Bockius, LLP
Parker Kenneth
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