Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2003-05-29
2004-12-07
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S141000
Reexamination Certificate
active
06829028
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a wide-viewing angle LCD technology, and more particularly to a wide-viewing angle LCD device with an electrode array suspended in an LC cell gap between two substrates which provides a transverse electrical field to drive LC molecules.
2. Description of the Related Art
Conventional TFT-LCDs (thin film transistor liquid crystal displays) devices, which use LC molecules with characteristics of rotary polarization and dual refractive effects so that incident light achieves bright and shade results, has a drawback known as a viewing angle dependency, that is, the contrast ratio decreases as the viewing angle increases. Thus presenting a difficulty in applying the TFT-LCD device to large-size display products.
Recently, various wide-viewing angle technologies have been proposed, such as an optical compensation film, a multi-domain vertical alignment (MVA) mode, and an in-plane switching (IPS) mode. The MVA mode LCD device uses a negative LC material, vertical alignment films, symmetrical protrusions and boundary electrical field effect, in which a pixel electrode array and a common electrode array formed on two substrates respectively provide a vertical electrical field to drive the LC molecules, thus increasing contrast ratio and response speed and solves problems of gray scale inversion and color shift. The IPS mode LCD device uses a TN (twisted nematic) LC material and a wide-viewing angle diffuser, in which a pixel electrode array and a common electrode array formed on a TFT array substrate provide a horizontal electrical field to drive the LC molecules, thus solves color shift caused by different viewing angles and increases the viewing angle.
EP No.0884626A2 discloses an MVA mode LCD device.
FIG. 1A
is a sectional diagram illustrating a conventional MVA mode LCD device.
FIG. 1B
is a diagram illustrating the variation in alignment of LC molecules shown in FIG.
1
A.
In
FIG. 1A
, an MVA mode LCD cell
10
comprises an upper glass substrate
12
, a lower glass substrate
14
, and an LC layer
16
with a negative anisotropy of dielectric constant filling in the space between the two glass substrates
12
and
14
. Two electrodes
18
I and
18
II and two vertical alignment layers
20
I and
20
II are formed on the inner surface of the glass substrates
12
and
14
. In general, the upper glass substrate
12
serves as a color filter substrate. The lower glass substrate
14
serves as a thin film transistor (TFT) substrate where a plurality of TFTs and active matrix drive circuits are formed. The electrode
18
II on the lower glass substrate
14
serves as a pixel electrode.
Furthermore, the LCD cell
10
has alignment-control structures including a plurality of first stripe-shaped protrusions
22
I formed on the inner surface of the upper glass substrate
12
and sandwiched between the electrode
18
I and the vertical alignment layer
20
I, and a plurality of second stripe-shaped protrusions
22
II formed on the inner surface of the lower glass substrate
14
and sandwiched between the electrode
18
II and the vertical alignment layer
20
II. When no voltage is applied, all the LC molecules are s aligned perpendicular to the vertical alignment layers
20
I and
20
II, respectively. For example, the LC molecules
16
A are aligned perpendicular to the glass substrates
12
and
14
. The LC molecules
16
B above the protrusions
22
I and
22
II are perpendicular to the vertical alignment layers
20
I and
20
II, so that the LC molecules
16
B pretilt at an angle to the glass substrates
12
and
14
.
In
FIG. 1B
, after a voltage is applied to the LCD cell
10
, the LC molecules
16
A and
16
B rotate toward a direction corresponding to an electrical field
24
to tilt at an angle depending on the voltage value. The arrows show the rotating directions of the LC molecules
16
A and
16
B. Within a pixel area, two alignment domains are formed at both sides of the first protrusion
22
I or the second protrusion
22
II. The LC molecules
16
A and
16
B disposed adjacent to the protrusions
22
I and
22
II has a pretilt effect before applying voltage, however, which conflicts with the rotating effect generated by the electrical field adjacent the electrode fringe after applying voltage, causing decreased response speed, disclination and poor viewing.
U.S. Pat. No. 5,995,186 discloses an IPS mode LCD device.
FIG. 2A
is a sectional diagram illustrating a conventional IPS mode LCD device.
FIG. 2B
is a sectional diagram illustrating the variation in alignment of LC molecules shown in FIG.
2
A.
An IPS mode LCD cell
30
comprises an upper glass substrate
32
, a lower glass substrate
34
and an LC layer
36
interposed in a space between the two glass substrates
32
and
34
and sandwiched between an upper alignment layer
38
I and a lower alignment layer
38
II. The lower glass substrate
34
, serving as a TFT array substrate, comprises a plurality of TFTs, scanning lines, data lines, common electrodes, pixel electrodes and an active matrix driving circuit. The two adjacent electrodes
40
I and
40
II serve as a data line and a common electrode, alternatively a common electrode and a pixel electrode. After a driving voltage is applied to the IPS mode LCD cell
30
, an in-plane electrical field
42
is generated between two adjacent electrodes
40
I and
40
II and parallel to the long axis of the LC molecules
36
A,
36
B and
36
C so that the LC molecules
36
A,
36
B and
36
C are rotated on the plane.
Since the data lines, common electrodes, pixel electrodes are provided on the lower glass substrate
34
, the intensity of the in-plane electrical field
42
weakens as the in-plane electrical field
42
is distanced from the lower glass substrate
34
. Thus, the intensity of the in-plane electrical field
42
for driving the LC molecules
36
A or
36
B is less than that for driving the LC molecule
36
C. The LC molecule
36
C adjacent to the lower glass substrate
34
where a higher intensity of in-plane electrical field
42
is applied, however, is difficult to drive on because of boundary conditions. The center of the LC layer
36
, such as the LC molecule
36
B, is more easily driven on but lacks a strong intensity of electrical field.
SUMMARY OF THE INVENTION
The present invention is a wide-viewing angle LCD device with an electrode array suspended in an LC cell gap between two substrates which provides a transverse electrical field to drive LC molecules.
Accordingly, the present invention provides a multi-domain vertical alignment (MVA) mode liquid crystal display (LCD) device. An upper glass substrate and a lower glass substrate are disposed parallel to each other, and a liquid crystal layer of positive dielectric anisotropy is formed in a space between the upper glass substrate and the lower glass substrate. A plurality of first protrusions is formed on the inner surface of the upper glass substrate. A plurality of common electrodes is formed on the tops of the first protrusions, respectively. A plurality of second protrusions is formed on the inner surface of the lower substrate, in which the first protrusions and the second protrusions are arranged alternately. A plurality of pixel electrodes is formed on the tops of the second protrusions, respectively, in which the pixel electrodes and the common electrodes are arranged alternately. After applying a voltage to the display device, a transverse electrical field is generated between the common electrode and the pixel electrode to drive the liquid crystal molecules, and two alignment domains are formed at both sides of the first protrusion.
Accordingly, the present invention also provides a multi-domain vertical alignment (MVA) mode liquid crystal display (LCD) device. An upper glass substrate and a lower glass substrate are disposed parallel to each other, and a liquid crystal layer of positive dielectric anisotropy is formed in a space between the upper glass substrate and the lower glass substrate. A plurality of first common electrodes is f
Chen Ching-Yih
Fan Yang-Yi
Lai Chih-Ming
Sheu Chia-Rong
Chowdhury Tarifur R.
Chung David
Industrial Technology Research Institute
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