Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-02-20
2004-08-24
Nguyen, Dung T. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S043000
Reexamination Certificate
active
06781653
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-7713, filed on Feb. 18, 2000, which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device implementing an embossed reflective electrode.
2. Discussion of the Related Art
Recently, liquid crystal display (LCD) devices with light, thin, and low power consumption characteristics are used in office automation equipment and video units and the like. Such LCDs typically use a liquid crystal (LC) with an optical anisotropy. The LC has thin and long LC molecules, which causes an orientational alignment of the LC molecules. Therefore, the alignment direction of the LC molecules is controlled by applying an electric field to the LC molecules. When the alignment direction of the LC molecules for each pixel is properly adjusted by applying an electric field, the transmittance for each pixel is changed. Therefore, the LCD can display image data.
At this time, an active matrix (AM) LCD, where a plurality of thin film transistors (TFTs) and pixel electrodes are arranged in the shape of an array matrix, is widely used because of its high resolution and superiority in displaying moving pictures. When each TFT serves to switch a corresponding pixel, the switched pixel transmits an incident light in a normally-black mode LCD. Since an amorphous silicon layer is relatively easily formed on a large inexpensive glass substrate, an amorphous silicon thin film transistor (a-Si:H TFT) is widely used.
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 therebetween. 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 transmissive LCD device requires a high, initial brightness, and thus electrical 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, and the battery can not be used for a lengthy period of time.
In order to overcome the problems described above, the reflective LCD has been developed. Since the reflective LCD device uses ambient light, it is light and easy to carry. In addition, the reflective LCD device is superior in aperture ratio to the transmissive LCD device.
FIG. 1
is a cross-sectional view illustrating a conventional reflective LCD device. As shown, between upper substrate
13
and lower substrate
11
, a liquid crystal layer
19
is interposed, and between the liquid crystal layer
19
and lower substrate
11
, a reflective electrode
16
is interposed. A common electrode
18
is interposed between the upper substrate
13
and liquid crystal layer
19
, and on the exterior surface of the upper substrate
13
, diffusing plate
21
, retardation film
23
, and polarizer
25
are sequentially formed.
The liquid crystal layer
19
has an optical anisotropy and controls the passage of light according to an electric field applied to the liquid crystal layer
19
. A certain medium having a similar optical anisotropy may be used instead of the liquid crystal layer
19
. The diffusion plate
21
, retardation film
23
, and polarizer
25
control the polarization state of light. Specifically, the diffusion plate
21
diffuses light to provide a wide viewing angle for users, while the retardation film
23
changes the polarization state of the incident light. In this case, a quarter-wave plate is used as the retardation film
23
. The polarizer
25
transmits only rays parallel to a transmittance axis of the polarizer
25
.
FIG. 2
is a plan view illustrating a pixel region of the conventional reflective LCD device. As shown, the pixel region “P” is defined by transverse gate line
33
and perpendicular data line
36
, which cross each other. On the pixel region “P,” the reflective electrode
16
is formed, and at the cross point between the gate and data lines
33
and
36
, a thin film transistor (TFT) “T” is formed as a switching device. The TFT “T” includes gate electrode
27
, source electrode
29
, and drain electrode
31
. The source electrode
29
and the gate electrode
27
are electrically connected with the data line
36
and gate line
33
, respectively. In addition, an active layer
30
is formed to overlap the gate electrode
27
. The active layer
30
serves as a channel. Electric charges pass through the channel to transfer image data between the drain and source electrodes
31
and
29
.
Still referring to
FIG. 2
, the reflective electrode
16
electrically contacts the drain electrode
31
via a drain contact hole
35
. The reflective electrode
16
made of an opaque metal reflects an ambient light to the liquid crystal layer
19
(see FIG.
3
). In addition, the reflective electrode
16
and common electrode
18
(see
FIG. 3
) apply electric signals to the liquid crystal layer
19
(see FIG.
3
).
Now, with reference to
FIG. 3
, a fabricating process for the conventional reflective LCD device is explained. At first, on the lower substrate
11
, a first metal is deposited and patterned to form the gate line
33
(see
FIG. 2
) and gate electrode
27
that is integrally protruded from the gate line
33
. The first metal is selected from a group consisting of chromium (Cr), molybdenum (Mo), aluminum (Al), aluminum alloy, and tungsten (W).
Then, a gate-insulating layer
28
is formed on the lower substrate
11
to cover the gate line
33
(see
FIG. 2
) and gate electrode
27
. The gate-insulating layer
28
is made of an inorganic insulating material, usually silicon oxide (SiO
X
) and silicon nitride (SiN
X
), or an organic insulating material, usually benzocyclobutene (BCB) and acryl.
On the gate-insulating layer
28
, an amorphous silicon layer and a doped amorphous silicon layer are deposited and patterned to form the active layer
30
in an island shape. Thereafter, on the gate-insulating layer
28
where the active layer
30
is formed, a second metal is deposited and patterned to form the data line
36
, source electrode
29
, and drain electrode
31
. The source electrode
29
is integrally protruded from the data line
36
, and the drain electrode
31
is spaced from the source electrode
29
. The second metal for the data line
36
, and source and drain electrode
29
and
31
is usually the same material as the first metal for the gate line and gate electrode
27
. Then, to cover the second metal layer, an organic insulating material, usually benzocyclobutene (BCB) or acryl is deposited as a passivation layer
36
. The passivation layer
36
is patterned such that the drain contact hole
35
is formed over the drain electrode
31
.
Thereafter, an opaque metal having a superior light-reflection property is deposited and patterned on the passivation layer
36
to form the reflective electrode
16
in the pixel region “P” of FIG.
2
. As previously explained, the reflective electrode
16
electrically contacts the drain electrode
31
via the drain contact hole. Aluminum (Al) is conventionally used for the reflective electrode
16
.
Thereafter, the lower substrate
11
is attached with the upper substrate
13
having the common electrode
18
on its inner surface, and the liquid crystal layer
19
is interposed between the upper and lower substrates
13
and
11
. At this point, the diffusion plate
21
is conventionally formed on the exterior surface of the upper substrate
13
. The diffusion plate
21
diffuses light such that high brightness and a wide v
Chung Jae-Young
Park Sung-II
Chung David
LG.Philips LCD Co. , Ltd.
McKenna Long & Aldridge LLP
Nguyen Dung T.
LandOfFree
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