Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-06-13
2003-01-07
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S111000
Reexamination Certificate
active
06504592
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a liquid crystal display, a method of manufacturing the liquid crystal display and a method of driving the liquid crystal display. More particularly, the present invention relates to a liquid crystal display which has a wide viewing angle, in which disturbance of alignment of liquid crystal molecules can be reduced and which is easily manufactured.
BACKGROUND OF THE INVENTION
Liquid crystal displays have been increasingly becoming popular as displays for information, image and the like. The liquid crystal displays have advantages of providing thin profile, small placing area and the like when compared with CRT (Cathode Ray Tube) displays.
Liquid crystal displays according to the present invention can be used in, for example, a display or monitor for a personal computer, a monitor for factory automation (FA), a home television set, a terminal monitor in a hospital, a library, a museum and the like, a monitor for an air traffic control tower and the like, a monitor used for reference of newspapers, documents in public offices and the like, a personal monitor in a school and a supplementary private school, a personal monitor for utilizing various media, a monitor in amusement facilities such as pachinko facilities, and the like. The liquid crystal displays according to the present invention can also be used as a light valve for projector type liquid crystal displays.
A recent liquid crystal display has image quality substantially equal to that of a CRT display. However, a viewing angle of the liquid crystal display is much narrower than that of the CRT display. Therefore, enlarging a viewing angle is one of the most important concerns in a liquid crystal display.
As a technology for enlarging a viewing angle of a liquid crystal display, there is considered using a liquid crystal display element which has a plurality of domains having different alignment directions in each pixel to obtain a wide viewing angle. Such prior art is disclosed in, for example, Japanese examined patent publication No. 58-43723, “Liquid Crystal Display Element”, Japanese patent laid-open publication No. 59-211019, “Liquid Crystal Display Device”, and Japanese patent laid-open publication No. 63-106624 (Japanese patent publication No. 2692693), “Liquid Crystal Display Panel”.
Referring to a “Liquid Crystal Display Panel” disclosed in Japanese patent laid-open publication No. 63-106624 as a prior art example, among the Japanese publications mentioned above, an explanation will be made on a prior art technology.
FIG. 28
is a plan view showing a conventional liquid crystal display according to this prior art example.
FIG. 28
corresponds to FIG. 1 described in the Japanese patent laid-open publication No. 63-106624.
FIG. 29
corresponds to FIG. 2 described in the Japanese patent laid-open publication No. 63-106624.
FIG. 30
corresponds to FIG. 3 described in the Japanese patent laid-open publication No. 63-106624.
FIG. 30
is a cross sectional view taken on line a-a′ of
FIG. 28
, and shows a cross section of one pixel of the conventional liquid crystal display device, that is, a liquid crystal display element.
With reference to
FIGS. 28 through 30
, a structure of the conventional liquid crystal display device will be described.
On a lower glass substrate
122
, there are formed a transparent lower display electrode
120
which is provided corresponding to each pixel, and a lower alignment film or layer
110
formed on the transparent lower display electrode
120
. On the lower glass substrate
122
, there is also formed a thin film transistor (TFT)
113
for driving the transparent lower display electrode
120
.
On an upper glass substrate
121
, there are formed a transparent upper display electrode
111
and a upper alignment film or layer
109
. The alignment films
109
and
110
are both made of polyimide.
A pixel B formed between the opposing transparent electrodes
111
and
120
has, for example, a square shape of 200 &mgr;m (micrometers) square, and a plurality of such pixels B are disposed in a matrix. At the center portion of the transparent display electrode, there is disposed a band shaped spacer
123
made of polyimide. As a result thereof, each pixel B is divided into a region X
131
and a region Y
132
by the band shaped spacer
123
. These divided regions X
131
and Y
132
are formed as shown schematically in
FIG. 16
which corresponds to
FIG. 2
of Japanese patent laid-open publication No. 63-106624. That is, the upper glass substrate
121
and the opposing lower glass substrate
122
are respectively rubbed in directions shown by arrows.
In order to show an effect of improvement in viewing angle dependence of viewing quality realized by this prior art liquid crystal display,
FIG. 31
shows a plan perspective view which illustrates rubbing directions and direction of twist of liquid crystal alignment between the upper and lower substrates when a direction of observation is changed by 45 degrees in bearing angle. In
FIG. 31
, there are shown divided regions X
131
, divided regions Y
132
, rubbing directions
1311
and
1312
in a first substrate, rubbing directions
1312
and
1322
, and a twist angle
127
of liquid crystal alignment between the upper and lower substrates.
FIG. 32
is a cross sectional view taken on line b-b′ of FIG.
31
and showing a rising direction of aligning force at the surface of a substrate and a rising direction of liquid crystal alignment by an electric field between the upper and lower substrates. In
FIG. 32
, a twist of liquid crystal molecules is not illustrated. In
FIG. 32
, there are shown liquid crystal material
105
, a direction of rising
106
of liquid crystal alignment caused by an electric field, the upper glass substrate
121
, a lower glass substrate
122
, a region X
131
, and a region Y
132
.
In this prior art liquid crystal display, as shown in
FIG. 31
, with respect to liquid crystal alignment in each of the divided regions or domains, a direction of spiral twist is the same, but as shown in
FIG. 32
, directions of angles from the substrate surface, i.e., pretilt angles, differ from each other.
Because of the difference of the angles from the substrate surface, when a voltage is applied between the upper and lower electrodes, direction
106
of rising up of liquid crystal molecules, which is also called direction of tilt, differ from each other as shown in FIG.
31
. Therefore, when light is irradiated from a direction which is inclined from the direction perpendicular to the substrate, optical characteristics of respective domains compensate with each other. As a result thereof, when the voltage is applied, viewing angle dependence is compensated with each other between domains having mutually different alignments in each pixel between the upper and lower substrates, and optical characteristics having small viewing angle dependency can be realized. Especially, when an image having gray shades is displayed, a phenomenon of gray shade inversion is not observed.
Otherliquid crystal display panels are also known which function based on the same principle as that of the above-mentioned liquid crystal display panel and which can be fabricated by smaller number of steps than that of the above-mentioned liquid crystal display panel Such liquid crystal display panels are described in “SID '92 Digest of U.S.A., p. 798”, “Japan Display '92 Digest, p. 591”, “SID '93 Digest of U.S.A., p. 269”, and the like.
In these examples, as in the first example, with respect to alignment of molecules of the liquid crystal material in each of the divided domains, direction of twist of a spiral is the same, but an angle to the substrate surface differs from each other. However, these liquid crystal display panels differ from the first example in a direction of aligning force applied to molecules of the liquid crystal material at the surface of the substrate and magnitude of angle of the aligning force.
In order to clarify the difference between these examples and
Hirai Yoshihiko
Ishii Toshiya
Kanoh Hiroshi
Kawada Kiyomi
Matsuyama Hiroaki
Michael Best & Friedrich LLC
NEC Corporation
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