Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-02-10
2003-12-30
Ngo, Julie (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S106000, C349S110000, C349S130000
Reexamination Certificate
active
06671025
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vertically aligned liquid crystal display device and a method of manufacturing the same and, more particularly, a liquid crystal display device having a structure in which the alignment direction of liquid crystal molecules is split into plural directions in a pixel and a method of manufacturing the same.
2. Description of the Prior Art
The active matrix type liquid crystal display device can prevent the crosstalk by providing a switch, which is turned off at the time of non-selection to cut off the signal, to each pixel, and thus exhibits the excellent display characteristic rather than the simple matrix type liquid. crystal display device. In particular, since the TFT (Thin Film Transistor) has the high driving capability in the liquid crystal display device which employs the TFTs as switches, such liquid crystal display device can exhibit the excellent display characteristic which is almost equivalent to the CRT (Cathode-Ray Tube).
FIG. 1
is a sectional view showing a structure of the normal TN (twisted nematic) liquid crystal display device.
The TN liquid crystal display device has a structure in which a liquid crystal
69
with positive dielectric anisotropy is sealed between two sheets of glass substrates
61
,
71
which are arranged to oppose to each other. The TFTs (not shown), pixel electrodes
62
, bus lines
63
, a flatting layer
64
, and an alignment film
66
are formed on an upper surface side of the glass substrate
61
. The pixel electrodes
62
are formed of ITO (Indium-tin Oxide) as transparent conductive material. A voltage is supplied to these pixel electrodes
62
at a predetermined timing via the bus lines
63
and the TFTs to correspond to the image. The flatting layer
64
is formed of insulating material to cover the pixel electrodes
62
and the bus lines
63
. A horizontal alignment. film
66
formed of polyimide, etc. is formed on the flatting layer
64
. An alignment process is applied to a surface of the alignment film
66
to decide the alignment direction of liquid crystal molecules when no voltage is applied. As the representative process of such alignment process, the rubbing process in which the surface of the alignment film is rubbed by a cloth roller along one direction is known.
While, a black matrix
72
, color filters
73
, a flatting layer
74
, an opposing electrode
75
, and an alignment film
76
are formed on a lower surface side of the glass substrate
71
. The black matrix
72
is formed of metal such as Cr (chromium) such that the light does not transmit into areas between the pixels. The color filters
73
consist of three color filters of red (R), green (G), and blue (B). Any one of R·G·B color filters
73
opposes to one pixel electrode
62
. The flatting layer
74
is formed to cover the black matrix
72
and the color filters
73
. The opposing electrode
75
formed of ITO is formed under the flatting layer
74
. The horizontal alignment film
76
is formed under the opposing electrode
75
. A surface of the alignment film
76
is also subjected to the rubbing process. In this case, the rubbing direction of the alignment film
66
is different by 90° from the rubbing direction of the alignment film
76
.
The glass substrates
61
,
71
are arranged to put spherical or cylindrical spacers
19
between them. A layer thickness of the liquid crystal
69
(referred to as a “cell thickness” hereinafter) is kept constant by the spacers
79
. The spacers
79
are formed of plastics or glass, for example.
In addition, polarizing plates (not shown) are stuck onto the lower surface side of the glass substrate
61
and the upper surface side of the glass substrate
71
. In the normally white mode liquid crystal display device, two sheets of polarizing plates are arranged such that their polarization axes intersect orthogonally with each other. In the normally black mode liquid crystal display device, two sheets of polarizing plates are arranged such that their polarization axes are positioned in parallel with each other.
In this disclosure, the substrate on which the TFTs, the pixel electrodes, the alignment film, etc. are formed is referred to as a “TFT substrate”, and the substrate on which the color filters, the opposing electrode, the alignment film, etc. are formed is referred to as a “CF substrate”.
FIGS. 2A and 2B
are schematic views showing an operation of the normally white mode TN liquid crystal display device. As shown in
FIGS. 2A and 2B
, in the normally white mode liquid crystal display device, two sheets of polarizing plates
67
,
77
are arranged such that their polarization axes intersect orthogonally with each other. Since the liquid crystal
69
with the positive dielectric anisotropy and the horizontal alignment films
66
,
76
are employed in the TN liquid crystal display device, the liquid crystal molecules
69
a
in the neighborhood of the alignment films
66
,
76
are aligned in the rubbing direction of the alignment films
66
,
76
. As shown in
FIG. 2A
, in the TN liquid crystal display device in which two sheets of polarizing plates
67
,
77
are arranged such that their polarization axes intersect orthogonally with each other, the liquid crystal molecules
69
a
sealed between two alignment films
66
,
76
change their alignment direction helically as their positions come close from one substrate
61
side to the other substrate
71
side. At this time, the light which passes through the polarizing plate
67
enters into the layer of the liquid crystal
69
as the linearly polarized light. Since the liquid crystal molecules
69
a
are aligned to be gradually twisted, the polarization direction of the input light is also twisted gradually and thus the light can pass through the polarizing plate
77
.
If the voltage applied between the pixel electrode
62
and the opposing electrode
75
is gradually increased, the liquid crystal molecules
69
a
start to rise along the direction of the electric field when the voltage exceeds a certain voltage (threshold value). When the sufficient voltage is. applied, the liquid crystal molecules
69
a
are directed substantially vertically to the substrates
61
,
71
, as shown in FIG.
2
B. At this time, the light which passes through the polarizing plate.
67
fails to pass through the polarizing plate
77
since its polarization axis is not rotated by the layer of the liquid crystal
69
.
In other words, in the TN liquid crystal display device, the direction of the liquid crystal molecules is changed from the almost parallel state to the substrates
61
,
71
to the vertical state thereto in response to the applied voltage, and the transmittance of the light which is transmitted through the liquid crystal display device is also changed correspondingly. Thus, desired images can be displayed on the liquid crystal display device by controlling the transmittance of the light every pixel.
Meanwhile, the good viewing angle characteristic cannot be achieved by the TN liquid crystal display device having the above structure. That is, the good display quality can be achieved if the image is viewed from the vertical direction to the substrates, nevertheless the contrast is extremely lowered if the image is viewed from the oblique direction and also the density is inverted.
As the method of improving the viewing angle characteristic of the TN liquid crystal display device, the alignment partition is known. This can be attained by providing more than two areas which have different alignment directions in one pixel. More particularly, one pixel region is divided into two areas or more, and then their alignment films are rubbed along different rubbing directions respectively. Accordingly, since the light which is leaked from one area can be cut off in the other area, reduction in the contrast in the half tone display can be improved.
In recent years, the vertically aligned liquid crystal display device is watched with interest as the liquid crystal display device which is superior in the
Ikeda Masahiro
Inoue Hiroyasu
Sawasaki Manabu
Tanaka Yoshinori
Taniguchi Yoji
Fujitsu Display Technologies Corporation
Greer Burns & Crain Ltd.
Ngo Julie
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