Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-09-18
2004-07-20
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06765642
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to an in-plane switching liquid crystal display (IPS-LCD). In particular, the present invention relates to an IPS-LCD with a compensation electrode structure and a method of forming the same.
2. Description of the Related Art
Liquid crystal displays (LCDs) may be classified by the orientation of the liquid crystal molecules between the spaced apart glass substrates. In a conventional twisted nematic LCD (TN-LCD), the liquid crystal molecules are twisted between the two substrates. In contrast, in an in-plane switching LCD (IPS-LCD), common electrodes and pixel electrodes are formed on a lower glass substrate (TFT substrate) and an in-plane electric field therebetween is generated to rearrange the liquid crystal molecules along the electric field. Accordingly, the IPS-LCD has been used or suggested for improving drawbacks of the conventional TN-LCD, such as a very narrow viewing angle and a low contrast ratio.
In order to achieve a better result of the in-plane electric field, a comb-shaped electrode array is built in the IPS-LCD to solve the problems such as an insufficient aperture ratio and crosstalk produced between data lines and common electrodes.
FIGS. 1A and 1B
are sectional diagrams of a conventional IPS-LCD, and
FIG. 1C
is a top view showing an electrode array within a pixel area of an IPS-LCD according to the prior art.
FIG. 1A
shows the alignment of the liquid crystal molecules at an off state, and
FIG. 1B
shows the alignment of the liquid crystal molecules at an on state. The IPS-LCD has a lower glass substrate
10
, an upper glass substrate
12
, and a liquid crystal layer
14
disposed in a space between the two parallel glass substrates
10
and
12
. On the lower glass substrate
10
, serving as a TFT substrate, a plurality of strip-shaped common electrodes
16
arranged as a comb-shape structure is patterned on the lower glass substrate
10
, an insulating layer
18
is deposited on the common electrodes
16
and the lower glass substrate
10
, and a plurality of strip-shaped pixel electrodes
20
arranged as a comb-shape structure is patterned on the insulating layer
18
.
As shown in
FIG. 1A
, before an external voltage is applied to the IPS-LCD, the liquid crystal molecules
14
A are aligned in a direction parallel to the lower glass substrate
10
. As shown in
FIG. 1B
, when an external voltage is applied to the IPS-LCD, an in-plain electric field is generated between the common electrode
16
and the pixel electrode
20
, resulting in a rotation of the liquid crystal molecules
14
B toward the in-plane electric field.
Depending on the material and the structure design of the common electrode
16
and the pixel electrode
20
, the conventional comb-shaped electrode array is classified as three types.
FIGS. 2A
to
2
C are sectional diagrams showing three types of the common electrode
16
and the pixel electrode
20
in the conventional comb-shaped electrode array. In the first type, as shown in
FIG. 2A
, the common electrode
16
and the pixel electrode
20
are patterned on the same plane and made of a transparent conductive material, such as ITO or IZO. In the second type, as shown in
FIG. 2B
, the common electrode
16
made of a non-transparent conductive material, such as Al and MoW, is patterned on the lower glass substrate
10
followed by depositing the insulating layer
18
, and then the pixel electrode
20
made of a transparent conductive material, such as ITO or IZO, is patterned on the insulating layer
18
. In the third type, as shown in
FIG. 2C
, the common electrode
16
and the pixel electrode
20
are patterned on the same plane and made of a non-transparent conductive material, such as Al and MoW. By comparison, the first type shown in
FIG. 2A
can provide an greater luminance to the IPS-LCD than the second type shown in FIG.
2
B and the third type shown in
FIG. 2C
, but provides a worsen view-angle characteristic than the second type and the third type. Also, the third type severely decreases the luminance of the IPS-LCD because most of the light is blocked by the non-transparent conductive material. Therefore, the second type shown in
FIG. 2B
is the most common type used in the conventional comb-shaped electrode array.
However, as to the second type, since the common electrode
16
and the pixel electrode
20
are patterned on different planes, it is possible to form different intervals between the common electrodes
16
and the pixel electrodes
20
on the electrode array caused by misalignment in the photolithography process.
FIG. 3A
is a sectional diagram showing an ideal case when a constant interval is formed between the common electrode
16
and the pixel electrode
20
.
FIG. 3B
is a transmittance-position diagram according to the electrode array shown in FIG.
3
A.
FIG. 4A
is a sectional diagram showing a practical case when different intervals are formed between the common electrodes
16
and the pixel electrodes
20
.
FIG. 4B
is a transmittance-position diagram according to the electrode array shown in FIG.
4
A. As shown in
FIGS. 3A and 3B
, the interval between the common electrode
16
and the pixel electrode
20
is a constant S
1
, and each S
1
spacing region has the same degree of in-plane electric field, resulting in the same capacitance and transmittance. In contrast, as shown in
FIGS. 4A and 4B
, the intervals between the common electrode
16
and the pixel electrode
20
are different, such as S
1
and S
2
, and the S
1
spacing region and the S
2
spacing region have different degrees of in-plane electric field, resulting in different capacitances and transmittances. In this practical case, demerits such as trip mura, shot mura and flicker are commonly found in the conventional IPS-LCD.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an IPS-LCD with a compensation electrode structure to form an alignment free electrode array to solve the demerits found in the prior art.
An IPS-LCD with a compensation electrode structure comprises a first glass substrate and a second glass substrate arranging in parallel to each other, and liquid crystal layer formed in a space between first glass substrate and the second glass substrate. A plurality of gate lines extending in a first direction is formed on the first glass substrate, and a plurality of data lines extending in a second direction are formed on the first glass substrate, wherein the second direction is perpendicular to the first direction. Thus, the data lines and gate lines constitute an array of pixel areas arranging in a matrix form. A TFT is formed in each pixel area.
A comb-shaped common electrode structure, a comb-shaped pixel electrode structure and a compensation electrode structure are disposed in each pixel area on the first glass substrate. The comb-shaped common electrode structure comprises a common line parallel to the gate line and at least two common electrodes extending in the second direction. The comb-shaped pixel electrode structure comprises a bar near the gate line and at least one pixel electrode which extends in the second direction and is inter-digitated with the two common electrodes. The compensation electrode structure comprises at least a first compensation electrode and a second compensation electrode that extend in the second direction and are patterned on the same plane with the pixel electrode. The two compensation electrodes overlap the two common electrodes respectively, and a first interval between the first compensation electrode and the pixel electrode is equal to a second interval between the pixel electrode and the second compensation electrode.
It is an advantage of the present invention that the same degree of in-plane electric field is formed within the first interval and the second interval to provide the same capacitance and transmittance. This eliminates trip mura, shot mura and flicker found in the conventional IPS-LCD.
This and other objective of the present invention will
Di Grazio Jeanne Andrea
Hannstar Display Corp.
Kim Robert H.
Rabin & Berdo P.C.
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