Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-02-12
2003-01-21
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S042000
Reexamination Certificate
active
06509943
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-6653, filed on Feb. 12, 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. More particularly, the present invention relates to an array substrate for use in a reflective LCD device.
2. Description of Related Art
Until now, the cathode-ray tube (CRT) has been developed for and is mainly used for the display systems. However, the flat panel display is beginning to make its appearance due to the requirement of the small depth dimensions, undesirably low weight and low voltage power supply. At this point, the thin film transistor-liquid crystal display (TFT-LCD) having a high resolution and small depth dimension has been developed.
During operation of the TFT-LCD, when a pixel is turned ON by 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 have an amorphous semiconductor layer. Advantageously, the amorphous silicon TFTs can be formed on low cost glass substrates using low temperature processing.
In general, the TFT-LCD transmits and image using light from the back light 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.
FIG. 6
shows a light transmittance respectively measured after light passes through each layers 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 GRAPH 1, which shows a transmittance (in brightness %) after light passes through each layer of the device. For this reason, the transmissive TFT-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. Moreover, there still exists a problem that the battery cannot be used for a long time.
In order to overcome the problem described above, the 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, compared to the transmissive TFT-LCD device. Namely, since the reflective TFT-LCD includes an opaque reflective material in the pixel of the conventional transmissive TFT-LCD, it reflects the ambient light.
Referring to the attached drawings, a reflective TFT-LCD device that is manufactured by a conventional method will now be explained in some detail.
In general, the TFT-LCD device includes a lower substrate, referred to as an array substrate, and an upper substrate, referred to as a color filter substrate.
FIG. 1
is a plan view illustrating one pixel of a conventional reflective TFT-LCD panel. An Nth gate line
8
and (N−1)th gate line
6
are arranged in a transverse direction in a matrix type. An Mth data line
2
and a (M+1)th data line
4
are arranged in a longitudinal direction in a matrix type as well. A gate electrode
18
is extended from the Nth gate line
8
. A source electrode
12
is extended from the Mth data line
2
and overlaps one end portion of the gate electrode
18
. A drain electrode
14
is spaced apart from the source electrode
12
and overlaps the other end portion of the gate electrodes
18
. The drain electrode
14
also electrically contacts a reflective electrode
10
via a drain contact hole
16
. The reflective electrode
10
has a plurality of convex surfaces
20
that reduce mirror effect and that increase a reflective area when the reflective electrode
10
reflects the ambient light. The reflective electrode
10
is made of an opaque metallic material such that it has an effect of reflecting light like a mirror. Thus, as forming a plurality of convex surfaces
20
that irregularly reflects the incident light, the mirror effect is lowered.
Referring to
FIGS. 2A
to
2
D that are cross-sectional views taken along line II—II of
FIG. 1
, the reference will now explain a plurality of the convex surfaces
20
in detail.
FIG. 2A
shows a step of forming a gate electrode
18
by depositing and then patterning a first metal layer. The first metal layer is deposited on a substrate
1
by a sputtering process. The first metal layer is a material selected from a group consisting of Chrome (Cr), Molybdenum (Mo), Aluminum (Al), Titanium (Ti), Tin (Sn), Tungsten (W) and Copper (Cu).
FIG. 2B
shows a step of forming a thin film transistor (TFT). A gate insulation layer
30
is formed on the substrate
1
and over the gate electrode
18
. The gate insulation layer
30
is made of silicon nitride (SiN
x
) or silicon oxide (SiO
2
). Then a semiconductor layer is deposited and patterned to form an island-shaped semiconductor layer
32
as an active layer. Source and drain electrodes
12
and
14
are formed by depositing and then patterning a second metal layer. Thus, the TFT is complete. Namely, the TFT is comprised of the gate electrode
18
, the gate insulation layer
30
, the island-shaped semiconductor layer
32
, the source electrode
12
and the drain electrode
14
. After that, a passivation layer
34
is formed over the TFT and on the gate insulation layer
30
in order to protect the TFT and to form a plurality of convex surfaces in a later step. At this time, since the passivation layer
34
has to have the convex surfaces
20
(see FIG.
1
), the passivation layer
34
is sufficiently thick. In other aspect, the passivation layer
34
can be a double-layer.
FIG. 2C
shows a step of forming a plurality of convex surfaces
20
. As shown, the passivation layer
34
is patterned to form the convex surfaces
20
. Thus, the thickness of the passivation layer
34
becomes thin. After that, patterning the passivation layer
34
forms a drain contact hole
16
that exposes a portion of the drain electrode
14
.
FIG. 2D
shows a step of forming a reflective electrode
10
as a pixel electrode. As shown, the reflective electrode
10
is formed on the passivation layer
34
by depositing and patterning the reflective conductive material. Thus, the reflective electrode
10
contacts the drain electrode
14
via the drain contact hole
16
. Further, the reflective electrode
10
covers the convex surfaces
20
, and causes scattered reflection when the ambient light is irradiated.
FIG. 3
is an enlarged view illustrating a portion “A” of FIG.
2
D and shows a convex surface
20
of conventional reflective TFT-LCD device. As shown, the convex surface
20
increases the reflective area of the reflective electrode
10
, and irregularly reflects the incident light
40
.
As described above, since the reflective TFT-LCD device does not use the backlight device, the battery can be used for a long time. Namely, the reflective TFT-LCD device reflects the ambient light on the reflective electrode
10
and then uses the reflected light to display the image.
However, in the conventional reflective LCD device described above, the passivation layer
34
is patterned twice to form a plurality of convex surfaces
20
and to form the drain contact hole
16
that electrically connects the drain electrode
14
to the reflective electrode
10
. Namely, the convex surfaces
20
is formed by patterning the passivation layer
34
, and then the passivation layer
34
is additionally patterned to form the drain contact hole
16
that exposes a portion of the drain electrode
14
. These are disadvantages of fabricating the reflective LCD device.
As above-mentioned, the conventional reflective LCD device needs separate patterning
Baek Heum-II
Kim Yong-Beom
LG. Philips LCD Co. Ltd.
Parker Kenneth
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