Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-03-12
2004-08-17
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06778243
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) and, more particularly, to a multi-domain LCD.
2. Description of the Related Art
Applying a voltage to a liquid crystal display (LCD) changes the alignment of liquid crystal molecules, and then the resulting optical characteristics, such as double refraction, optical rotation, dichromatism, optical confusion and optical scattering cause display variations. Compared with the electric-optical materials used in other optical devices, liquid crystal molecules can distribute substantial variations in optical characteristics with low voltage and low power consumption, and without further treatments. In addition, LCD has the advantages of a thin profile and a lightweight. Therefore, as we know, LCDs play an important role in the flat display market.
Display modes in LCDs differ with each other according to different types of liquid crystal molecules utilized therein. One mode, electrically controlled birefringence (ECB), employs an applied electric field to control the multi-refraction characteristics of the liquid crystal molecules. For example, nematic liquid crystal molecules having a negative anisotropy of dielectric constant are utilized together with a vertical alignment layer. When the applied voltage exceeds a threshold voltage, the liquid crystal molecules that are originally aligned perpendicular to the vertical alignment layer will rotate to an angle corresponding to the applied electric field. As well, to further control the alignment of the liquid crystal molecules, an alignment-control structure is fabricated to increase the number of alignment domain in each pixel area. It is thus possible to reach the goals of wide view angle and high contrast.
Referring to FIG.
1
and
FIG. 2
,
FIG. 2
is a top view of the alignment-control structure in a conventional LCD cell
10
, and
FIG. 1
is a schematic cross-sectional diagram along line I-I′ of FIG.
2
. As shown in
FIG. 1
, the LCD cell
10
comprises an upper glass substrate
12
, a lower glass substrate
14
, and a liquid crystal layer
16
with a negative anisotropy of dielectric constant filling in the space between the two glass substrates
12
and
14
. Two electrodes
18
and
22
and two vertical alignment layers
20
and
24
are respectively formed on the inner surface of the glass substrates
12
and
14
. Two polarizers
26
and
28
are respectively formed on the outer 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
22
on the lower glass substrate
14
serves as a pixel electrode
22
. Furthermore, the LCD cell
10
has a plurality of first strip-shaped protrusions
30
and second strip-shaped protrusions
32
respectively formed above the electrodes
18
and
22
to serve as the alignment-control structures.
As shown in
FIG. 2
, two transversely-extending gate lines
36
and two lengthwise-extending signal lines
38
define a pixel area. A TFT structure
39
is formed near the intersection of the gate line
36
and the signal line
38
, and the pixel electrode
22
is formed on the pixel area. On the upper glass substrate
12
, the first strip-shaped protrusions
30
extend transversely and pass through the gate lines
36
. On the lower glass substrate
14
, the second strip-shaped protrusion
32
extends transversely and passes through the center of the pixel electrode
22
. In this way, the first protrusions
30
and the second protrusions
32
extend in parallel to each other and are arranged alternately.
FIGS. 3 and 4
are schematic diagrams showing the variation in alignment of the liquid crystal molecules. As shown in
FIG. 3
, when no voltage is applied, the liquid crystal layer
16
having a negative anisotropy of dielectric constant is arranged between the vertical alignment layers
20
and
24
, all the liquid crystal molecules in the liquid crystal layer
16
are aligned perpendicular to the vertical alignment layers
20
and
24
, respectively. For example, the liquid crystal molecules
16
A are aligned perpendicular to the glass substrates
12
and
14
. The liquid crystal molecules
16
B above the protrusions
30
and
32
are vertical to the perpendicular alignment layers
20
and
24
above the protrusions
30
and
32
, so that the liquid crystal molecules
16
B above the protrusions
30
and
32
are positioned at an angle to the glass substrates
12
and
14
.
As shown in
FIG. 4
, after the voltage is applied to the LCD cell
10
, the liquid crystal molecules will rotate perpendicular to the electric field. The arrows show the rotating directions of the liquid crystal molecules. For example, the liquid crystal molecules
16
B
1
, aligned from the upper right toward the lower left in the beginning, and will be rotated in a clockwise direction after the voltage is applied so that the liquid crystal molecules
16
B
1
fall in the direction parallel to the vertical alignment layers
20
and
24
. Consequently, the adjacent liquid crystal molecules
16
A
1
will rotate in a clockwise direction according to the behavior of the liquid crystal molecules
16
B
1
. In a similar manner, the liquid crystal molecules
16
B
2
are positioned from the upper left toward the lower right in the beginning, and then fall in the direction parallel to the vertical alignment layers
20
and
24
and rotate in a counterclockwise direction while the voltage is applied. As a result, the adjacent liquid crystal molecules
16
A
2
will rotate in a counterclockwise direction according to the behavior of the liquid crystal molecules
16
B
2
.
FIG. 5
is a top view showing the alignment domain of the liquid crystal layer
16
. After a voltage is applied, these liquid crystal molecules will rotate to parallel to the direction of electric field. Upon application of voltage to the LCD cell
10
, part of the liquid crystal molecules
16
A
1
and
16
B
1
rotate in a clockwise direction and another part of liquid crystal molecules
16
A
2
and
16
B
2
rotates in a counterclockwise direction. Accordingly, two alignment domains are formed both sides of the second protrusion
32
in a pixel area. The arrows show the alignment direction.
However, since the alignment-control structure only forms two domains in a pixel area, this cannot satisfy the requirements of a wide view angle and a high contrast in the LCD. Also, the alignment-control structure is the strip-shaped protrusions
30
and
32
, so the aperture ratio of the LCD is reduce, resulting in decreased brightness and lower contrast. Thus, a multi-domain LCD solving the aforementioned problems is called for.
SUMMARY OF THE INVENTION
The present invention provides rectangular protrusions in one pixel area to serve as the alignment-control structure.
The LCD includes an upper substrate having an upper electrode on the inner surface of the upper substrate, a lower substrate having a lower electrode on the inner surface of the lower substrate, and a liquid crystal layer with a negative anisotropy of dielectric constant filling the space between the upper substrate and the lower substrate. An electric field is formed between the upper electrode and the lower electrode. A plurality of first alignment-control structures are arranged on the inner surface of the upper substrate, an upper concave is formed between two adjacent first alignment-control structures, and an upper inclined plane is formed between the upper concave and the first alignment-control structure. A plurality of second alignment-control structures are arranged on the inner surface of the lower substrate, a lower concave is formed between two adjacent second alignment-control structures, and a lower inclined plane is formed between the lower concave and the second alignment-control structure. The first alignment-control structure is positioned abo
Au Optronics Corp.
Kim Richard H
Kim Robert H.
Ladas & Parry
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