Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2001-12-28
2004-12-21
Eckert, George (Department: 2815)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S042000, C349S114000, C257S059000, C257S072000
Reexamination Certificate
active
06833883
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to liquid crystal display devices, and more particularly, to an array substrate for reflective and transflective liquid crystal display devices.
2. Description of the Background Art
Generally, a reflective liquid crystal display device does not need to equip an additional light source such as a back light because it can substitute an external light source for the back light. A transflective liquid crystal display device has both properties of the reflective liquid crystal display device and a transmissive liquid crystal display device. Because the transflective liquid crystal display device utilizes both of the back light and the external light source, it can save power consumption.
FIG. 1
illustrates a liquid crystal panel for a conventional transflective liquid crystal display device. The conventional transflective liquid crystal display device
11
has an upper substrate
15
that includes a color filter
18
a transparent common electrode
13
and a lower substrate
21
that includes a pixel region “P”, a pixel electrode
19
, thin film transistor and an array of gate lines
25
and data lines
27
. The color filter
18
includes a black matrix
16
and sub-color filters R, G and B. The pixel electrode
19
has a transmission portion “A” and a reflection portion “C”. Liquid crystal
23
is interposed between the upper substrate
15
and the lower substrate
21
. The lower substrate
21
is also referred to as an array substrate with thin film transistors “T”, switching elements, arranged in a matrix on the array substrate
21
. A plurality of horizontal gate lines
25
and a plurality of vertical data lines
27
cross each other defining the pixel region “P”. If the transparent pixel electrode
19
and the transmission portion “A” are omitted from the transflective liquid crystal display device, it becomes a reflective liquid crystal display device.
FIG. 2
is a plan view illustrating a partial array substrate for a conventional reflective liquid crystal display device. As shown in the figure, a plurality of gate lines
25
and a plurality of data lines
27
cross each other defining a pixel region “P”. A thin film transistor “T”is formed at a crossing portion of the gate line
25
and the data line
27
. The thin film transistor “T” usually includes a gate electrode
32
, a source electrode
33
, a drain electrode
35
and an active layer
34
. A pixel electrode
19
is formed in the pixel region “P” and the thin film transistor “T” connected to the drain electrode
35
drives the liquid crystal
23
of
FIG. 1. A
reflective electrode, which is formed of opaque conductive metal having a high reflexability, is substituted for the pixel electrode
19
in the reflective liquid crystal display device. The opaque conductive metal is selected from a group consisting of aluminum (Al) and aluminum alloys (AlNd, for example), for example.
Because the reflective liquid crystal display device uses an external light source, incident light from the external light source passes through the upper substrate (not shown) and is then reflected at the reflective electrode
10
on the array substrate
21
. The reflected light subsequently passes through the liquid crystal and thereby polarization properties of the light are changed according to birefringence properties of the liquid crystal. Color images can be displayed when the light passing through the liquid crystal colors the color filter.
FIG. 3
is a cross-sectional view taken along III—III of
FIG. 2
according to the conventional. As shown in the figure, a gate electrode
32
and a gate line
25
of
FIG. 2
are formed on a substrate
21
. A gate insulating layer
41
is formed on the substrate
21
and on the gate electrode
32
. An active layer
34
is formed on the gate insulating layer
41
and partially overlapped with a source electrode
33
and a drain electrode
35
. The source electrode
33
, the drain electrode
35
and the data line
27
are formed on the active layer
34
. A thin film transistor includes the gate electrode
32
, the source electrode
33
, the drain electrode
35
and the active layer
34
. A passivation layer
43
made of insulating material is formed on the thin film transistor. The passivation layer
43
is subsequently patterned to form a drain contact hole
45
exposing a part of the drain electrode
35
. A reflective electrode
19
contacts the drain electrode
35
through the drain contact hole
45
. The material for the reflective electrode
19
is selected from a group including aluminum (Al) and aluminum alloy (AlNd, for example), etc.
FIG. 5
is a cross-sectional view taken along line V—V of
FIG. 4
according to the conventional. A thin film transistor “T” including a gate electrode
32
, a source electrode
33
, a drain electrode
35
and an active layer
34
is formed and a first passivation layer
43
is formed on the thin film transistor “T”. The first passivation layer
43
is formed by depositing a transparent organic insulating material such as benzocyclobutene (BCB) and acrylic resin. A drain contact hole
45
that exposes a part of the drain electrode
35
is formed and a etching hole
53
is formed by etching the first passivation layer
43
corresponding to the transmission hole
53
in the pixel region “P”. A reflective electrode
19
a
that contacts the drain electrode
35
through the drain contact hole
45
is formed in the pixel region “P”. The reflective electrode
19
a
is formed of aluminum (Al) and aluminum alloys (AlNd, for example), etc. A second passivation layer
47
is formed on the reflective electrode
19
a
and patterned to expose the reflective electrode
19
a
corresponding to the drain contact hole
45
. The second passivation layer
47
is formed of insulating material such as silicon oxide (SiO
2
) or silicon nitride (SiN
X
), for example. A transparent pixel electrode
19
b
that contacts the exposed reflective electrode
19
a
through the patterned second passivation layer
47
is formed on the second passivation layer
47
.
Several masks for patterning array elements of the array substrate are used in the manufacturing of the conventional reflective and transflective liquid crystal display device. An align key for accurate aligning of the mask and the substrate is formed on the corner of the substrate simultaneously with the gate line or the data line forming process. The shape of the align key has unevenness. Accordingly, a detector aligns the mask and the substrate by irradiating light onto the uneven surface of the align key and sensing the light reflected from the surface of the align key.
FIG. 6
is a plan view illustrating a partial array substrate having a coplanar type polysilicon thin film transistor for a conventional transflective liquid crystal display device. A gate line
71
and a data line
84
cross each other defining a pixel region “P” and a thin film transistor “T” is formed at a crossing portion of the gate line
71
and the data line
84
. The thin film transistor “T” is a polysilicon thin film transistor that includes a polysilicon active layer and has a coplanar structure in which a gate electrode
70
is formed under a source electrode
80
and a drain electrode
82
. A gate pad
74
and a data pad
86
, which receive an external signal, are formed respectively at one end of the gate line
71
and the data line
84
. The gate pad
74
and the data pad
86
respectively contact a gate pad terminal
94
and a data pad terminal
96
that are formed of transparent conductive material. The thin film transistor “T” includes the gate electrode
70
, the source electrode
80
, the drain electrode
82
and an active layer
66
. The active layer
66
has an active layer expanded portion
67
in the pixel region “P”. A storage line
72
is formed parallel to the gate line
71
with a same material as that of the gate line
71
arid has a storage line expanded potion
73
in the pixel region “P”. The pixel electrode
63
contacts the drain electrode
82
. A stor
Choi Jae-Sik
Park June-Ho
Birch & Stewart Kolasch & Birch, LLP
Eckert George
Landau Matthew C
LG. Philips LCD Co. Ltd.
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