Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-05-28
2004-06-29
Ngo, Huyen (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S038000, C349S043000, C349S044000
Reexamination Certificate
active
06757041
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to a manufacturing method for a liquid crystal display (LCD) unit, and more particularly to a manufacturing method for an in-plane switching mode liquid crystal display (LCD) unit.
BACKGROUND OF THE INVENTION
As the technique is developing, it is the trend that the liquid crystal display (LCD) takes the place of the conventional picture tube display and becomes the main stream in the market. Please refer to FIG.
1
(
a
). FIG.
1
(
a
) is a diagram illustrating the circuit of a pixel unit in a liquid crystal display according to the prior art. It is composed of a display unit
12
, a storage capacitor
13
, and a switching unit accomplished by a thin film transistor
11
. Regarding the structure of the display unit
12
, it is mainly divided into two types at present. The common structure is a twisted nematic liquid crystal display (TN-LCD), as shown in FIG.
1
(
b
). In FIG.
1
(
b
), the data electrode
121
and the common electrode
122
are mounted at both sides of the liquid crystal molecule
123
. The cell gap between the upper and lower glasses is “d.” Through controlling the potential difference between the data electrode
121
and the common electrode
122
(the direction of the electric field is shown in a dotted line in the diagram), the liquid crystal molecule
123
can stand erect to form the included angle between the liquid crystal molecule
123
and the Z-axis. Therefore, the light-pervious rate will follow to be changed according to the included angle and the pixel brightness can be controlled. However, due to the rotation way of the liquid crystal molecule in the above display unit structure, the distribution of plural refractions is very different while the watcher has different visual angles, for example, in the inclined directions of A—A′ and B—B′ (as shown in FIG.
1
(
b
)). Besides, the pervious rate will be very different and the disadvantage that the bigger visual angle cannot be provided will be existed. Therefore, the above display unit structure has its limitation indeed, especially that the superficial size of the display panel is getting increased at the present time.
Compared with the second type structure (TN-LCD), the first type structure (TN-LCD) has the disadvantage that the rotation way of the liquid crystal molecule has a smaller visual angle. On the contrary, the display unit structure
12
in the second type has a better range of visual angle. Please refer to FIG.
1
(
c
). FIG.
1
(
c
) is a diagram illustrating the display unit structure
12
of an in-plane switching mode (IPS mode) according to the prior art. It is clear in the diagram that the data electrode
121
and the common electrode
122
are mounted at the same side of the liquid crystal molecule
123
. Therefore, while the potential difference between the data electrode
121
and the common electrode
122
is changed (the direction of the electric field is shown in a dotted line in the diagram), the liquid crystal molecule
123
will take Z-axis as the axle center and rotate around it. The light-pervious rate will follow to be changed and the pixel brightness control will be accomplished. The rotation way of the liquid crystal molecule in this kind of display unit structure will not have a light-pervious rate change while the watcher has different visual angles. Therefore, it has the advantage that a bigger visual angle can be provided, and it will help a lot for manufacturing the display panel with bigger size.
Please refer to FIGS.
2
(
a
) and
2
(
b
). FIG.
2
(
a
) is a top view showing the pixel unit structure of the in-plane switching mode (IPS mode) in the first conventional thin film transistor LCD according to the prior art. FIG.
2
(
b
) is a sectional view along the A-B line segment showing the pixel unit structure of the in-plane switching mode (IPS mode) in the first conventional thin film transistor LCD according to the prior art. The pixel unit structure is accomplished by the following process:
(a) forming a first mental layer on the substrate
20
and defining thereon a gate line
21
, a common electrode
22
of the display unit, and a wiring pad
23
needed for the periphery (the first photo etching process (PEP)).
(b) depositing a gate insulation layer
24
, a semi-conductive layer, and a relatively high doped semi-conductive layer, and additionally, defining a channel structure
25
(the second photo etching process (PEP)).
(c) forming a second mental layer and defining a source/drain electrode region
26
of thin film transistor, a data line
27
, and pixel electrode
28
of the display unit (the third photo etching process (PEP)).
(d) depositing a passivation layer
29
and defining a contact window
231
on the wiring pad
23
(the fourth photo etching process (PEP)).
It is clear in FIGS.
2
(
a
) and
2
(
b
) that the common electrode
22
and pixel electrode
28
of the display unit are respectively accomplished from the first mental layer and the second mental layer, which forms two flats with different altitudes. Therefore, the curve of the data voltage and the pervious rate is asymmetric, as shown in FIG.
2
(
c
). Besides, the display image will have the drawbacks of image-sticking and flicker. Since the common electrode
22
and pixel electrode
28
of the display unit are respectively accomplished from the first mental layer and the second mental layer in two different photo etching processes, the two electrodes will unavoidably have the problem of misalignment, which will cause uneven light-pervious rate and mura.
In order to improve the above drawbacks, another conventional pixel unit structure is developed, as shown in FIG.
3
. FIG.
3
(
a
) is a top view showing the pixel unit structure of the in-plane switching mode (IPS mode) in the second conventional thin film transistor LCD according to the prior art. FIG.
3
(
b
) is a sectional view along the A-B line segment showing the pixel unit structure of the in-plane switching mode (IPS mode) in the second conventional thin film transistor LCD according to the prior art. The pixel unit structure is accomplished by the following process:
(a) forming a first mental layer on the substrate
30
and defining thereon a gate line
31
, a common electrode
32
of the display unit, a lower electrode
320
for storing capacitance, and a wiring pad
33
needed for the periphery (the first photo etching process (PEP)).
(b) depositing a gate insulation layer
34
, a semi-conductive layer, and a relatively high doped semi-conductive layer, and additionally, defining a channel structure
35
(the second photo etching process (PEP)).
(c) forming a second mental layer and defining a source/drain electrode region
36
of thin film transistor, a data line
37
, and an upper electrode
38
for storing capacitance (the third photo etching process (PEP)).
(d) depositing a passivation layer
39
and respectively defining contact windows
331
,
381
, and
321
on the wiring pad
33
, the upper electrode
38
for storing capacitance, and the common electrode
32
(the fourth photo etching process (PEP)).
(e) forming a third mental layer and defining two comb-shaped electrodes
382
and
322
to have electric contact with the upper electrode
38
and the common electrode
32
through the contact windows
381
and
321
respectively (the fifth photo etching process (PEP)).
It is known from the above description that the two comb-shaped electrodes
382
and
322
are accomplished at the flats with same altitudes in the same photo etching process. Since there is no altitude difference between the two comb-shaped electrodes
382
and
322
, it will not result in the problem of misalignment. Although the drawback of the former technique is solved, however, the steps of the photo etching process (PEP) are too many, which will lower the yield efficiency and increase the cost. Hence, how to rectify the foresaid conventional drawback has become the main purpose of the present invention.
SUMMARY OF THE INVENTION
It is an object of the present invention to provid
Hannstar Display Corp.
Haverstock & Owens LLP
Ngo Huyen
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