Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-08-09
2004-11-16
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S043000, C349S138000
Reexamination Certificate
active
06819384
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) panel capable of reducing a persistence degree and a development method thereof.
2. Description of the Related Art
Each of
FIGS. 31 and 32
is a schematic sectional view showing a structure of one pixel of an LC panel.
FIG. 31
shows a state where no voltage is applied, and
FIG. 32
shows a state where a voltage is applied.
The LCD panel includes substrates
10
and
20
opposing to each other, and a sealed-in nematic liquid crystal
30
having an anisotropic dielectric positive constant. In the substrate
10
, a flat electrode
12
, a dielectric layer
13
and a vertically oriented layer
14
are formed on a face of a transparent insulating substrate
11
, for example, a glass substrate, and on the other face thereof, a polarizer
15
is formed. In the substrate
20
, a common electrode
23
is formed on one face of a transparent substrate
21
, for example, a glass substrate, an insulating layer
24
is formed thereon, a pixel electrode
25
is formed on the insulating layer
24
, and further an insulating layer
26
and a vertically orientated later
27
are formed thereon. On the other face of the substrate
21
, a polarizer
28
is formed. Transmission axes of the polarizers
15
and
28
perpendicularly cross over each other.
When backlight in the direction shown by arrows in
FIG. 31
enters into the LCD panel, the light is transformed into linearly polarized light by the polarizer
28
. When the flat electrode
12
, the common electrodes
23
and the pixel electrode have the same potential, the liquid crystal
30
effects no change in the plane of polarization of the linearly polarized light, and therefore the linearly polarized light cannot be transmitted through the polarizer
15
, resulting in a dark state.
When, as shown in
FIG. 32
, the flat electrode
12
and the common electrode
23
has the same potential but the pixel electrode
25
is applied with a potential different from the both former electrodes, an electric field arises. Dotted lines of
FIG. 32
show the lines of electric force. Liquid crystal molecules are inclined relative to an incident light direction under influence of the electric field to cause birefringence, and part of the light can transmit through the polarizer
15
, resulting in a bright state.
Since the common electrode
23
and the pixel electrode
25
are made of an opaque metal, behaviors of liquid crystal molecules over the electrodes are not problematic in terms of display.
If the flat electrode
12
does not exist, liquid crystal molecules between the pixel electrode and the common electrode
23
tend to reduce inclination thereof, which will produces the drop region of transmittance. The flat electrode
12
makes the electric field between the common electrode
23
and the pixel electrode
25
asymmetric so as to contributes to prevent the transmittance from locally dropping. The dielectric layer
13
reinforces the lateral component of the electric field in the liquid crystal
30
to make it possible for the liquid crystal
30
to be driven with lower applied voltage. The common electrode
23
and the pixel electrode
25
each are stripe electrodes extending in the direction perpendicular to the sheet of
FIG. 32
, and alternately formed on the top and bottom surfaces of the insulting layer
24
. The insulating layer
24
is for preventing common electrodes and pixel electrodes from short-circuiting at positions where the both overlap as will be described later. The insulating layer
26
is for reducing the persistence degree.
FIG. 33
shows an electrode pattern of one pixel, formed in the substrate
20
of FIG.
31
.
FIGS. 34 and 35
are patterns of the pixel electrode
25
and the common electrode
23
, respectively, of FIG.
33
.
In
FIG. 33
, a data line DL
1
and a scan line SL
1
cross over each other with an insulating layer interposing therebetween. Each of the pixel electrode
25
and the common electrode
23
has a stripe section and a peripheral section connecting ends of the stripe section. The lines of the stripe section are inclined 45 degrees to each of the scan line SL
1
and the data line DL
1
.
When the potential of the scan line SL
1
goes high, a TFT
29
is turned on to apply the potential of the data line DL
1
onto the pixel electrode
25
and generate an electric field between the stripe electrodes of the pixel electrode
25
and the common electrode
23
. The longitudinal direction of the upper half of the stripe electrodes is different from that of the lower half of the stripe electrodes by 90 degrees as shown in
FIG. 33
, whereby the LCD panel has wider range of viewing angles than in a case where the both halves of the stripe electrodes are parallel to each other.
The common electrode
23
A has peripheral protrusions which are connected to the common electrodes of adjacent pixels not shown.
FIG.
36
(A) is an enlarged partial view near a crossover of a stripe electrode and the peripheral section of FIG.
33
. FIG.
36
(B) shows the lines of electric force with dotted lines near the crossover when a voltage is applied between the pixel electrode
25
and the common electrode
23
.
A peripheral section of the pixel or common electrode has crossover portions to stripe electrodes of the common or pixel electrodes with the insulating layer interposing therebetween since a pixel has a rectangular shape, and each of the pixel electrode
25
and the common electrode
23
has stripe electrodes in parallel to each other and has a continuous shape. For example, a side
251
of the pixel electrode
25
is connected to a side
252
of the peripheral section, and a side
231
of the common electrode
23
is parallel to the side
251
, while the side
231
crosses over the side
252
at an acute angle.
FIG. 37
is a schematic sectional view showing inclination of liquid crystal molecules between the pixel electrode
25
and the common electrode
23
of one pixel of the LCD panel when a voltage is applied therebetween.
In
FIG. 32
, a structure between the pixel electrode
25
and the liquid crystal
30
is different from that between the common electrode
23
and the liquid crystal
30
, which causes persistence.
In FIG.
36
(B), since the side
252
crosses over the side
231
at an acute angle, an electric field therebetween near the crossover is stronger than that between the parallel sides. Further, a direction of electric field strength near the crossover is different from that between the parallel sides. Due to such conditions, a transmittance-voltage characteristic near the crossover is different from that between the parallel portion, causing not only degradation of an image quality but also persistence.
In
FIG. 37
, since the insulating layer
26
exists above the pixel electrode
25
, application of an electric field in this portion is useless and effective application of the electric field to the liquid crystal
30
is prevented. If the insulating layer
26
is omitted in order to solve this problem, it causes more persistence since the insulating resistance of the vertically oriented layer
27
is low. If the pixel electrode
25
is exposed to the liquid crystal
30
, not only is the degree of persistence enhanced, but liquid crystal molecules also decompose. Further, since the top surface of a pixel electrode
25
is flat, it is not possible to effectively apply an electric field to the liquid crystal
30
in relation to transmittance, which prevents achieving higher contrast display.
In development of an LCD panel, measurement of a persistence degree is performed at each trial when a structure or material of the LCD panel is changed in order to reduce the persistence degree to a value lower than a given value, and it takes, for example, 48 hours to measure the persistence degree in each trial, which makes a development term thereof longer.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a liquid crystal display panel capable of reducing a p
Nakanishi Yohei
Sasabayashi Takashi
Tasaka Yasutoshi
Yoshida Hidefumi
Duong Tai
Fujitsu Display Technologies Corporation
Greer Burns & Crain Ltd.
Ton Toan
LandOfFree
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