Liquid crystal cells – elements and systems – With specified nonchemical characteristic of liquid crystal... – Within smectic phase
Reexamination Certificate
2001-12-17
2003-10-07
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
With specified nonchemical characteristic of liquid crystal...
Within smectic phase
C349S129000
Reexamination Certificate
active
06630981
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display, and more particularly to a liquid crystal display using ferroelectric or anti-ferroelectric liquid crystal with an improved visible angle dependency.
The liquid crystal display has widely been used in various fields for watches, pocket calculators, word processors and personal computers. The liquid crystal phase used in the liquid crystal display is normally nematic phase. The liquid crystal display using the nematic liquid crystal has a serious problem in visible angle dependency, wherein display may change in color over angles of view since the nematic liquid crystal varies in transmittance of light over view angles. The range of view angle free of any change in color is relatively narrow.
The following description will focus on the reason why the nematic liquid crystal varies in transmittance of light over view angles. The liquid crystal molecule has a slender shape having a longitudinal axis. The transmittance of light through the liquid crystal depends upon an included angle defined by the longitudinal axis of the slender-shaped liquid crystal molecule and a direction of a ray of light transmitting through the liquid crystal. For a nematic liquid crystal, it is convenient to direct the attention onto the longitudinal axis of the liquid crystal molecules in the center area of a display cell, excluding liquid crystal molecules adjacent to a pair of substrates sandwiching the twisted liquid crystal. If no voltage is applied, the liquid crystal molecules in the center area of the cell are oriented so that the longitudinal axis of the liquid crystal molecules is directed in parallel to the substrate surface. If, however, a voltage is applied, the liquid crystal molecules are moved in a plane perpendicular to the substrate surface so that the longitudinal axis of the liquid crystal molecules is risen up and tilted from the substrate surface as illustrated in FIG.
1
. Since the direction of the ray of light depends upon a relative position of observer to the screen of the display, the included angle defined by both the longitudinal axis of the liquid crystal molecule and the direction of the ray of light is varied depending upon the change in the relative position of observer to the screen of the display. As described above, the transmittance of the light through the liquid crystal depends upon the included angle defined by both the longitudinal axis of the liquid crystal molecule and the direction of the ray of light.
FIG. 1
is a schematic view illustrative of the twisted nematic liquid crystal molecule which is tilted and risen up from the substrate surface to explain the dependency upon the view angle of the twisted nematic liquid crystal molecules. For example, as illustrated in
FIG. 1
, the liquid crystal molecule
5
in the center area of the liquid cell
11
is risen so that the longitudinal direction thereof is tilted from the substrate surface. The ray of light
14
a
having been transmitted through the liquid crystal cell is largely different in direction from the longitudinal axis of the liquid crystal molecule, for which reason the included angle defined by the longitudinal axis of the liquid crystal molecule and the direction of the ray of light
14
a
is large. Since the transmittance of the ray of light having been transmitted through the liquid crystal depends upon the included angle defined by the longitudinal axis of the liquid crystal molecule and the direction of the ray of light
14
a
, the transmittance of the ray of light
14
a
through the liquid crystal is low. Accordingly, if the observer views the screen in the direction of an arrow mark
13
a
in parallel to the ray of light
14
a
, then the transmittance of the ray of light
14
a
through the liquid crystal is low. In contrast, the ray of light
14
b
having been transmitted through the liquid crystal cell
11
is almost the same in direction as the longitudinal axis of the liquid crystal molecule, for which reason the included angle defined by the longitudinal axis of the liquid crystal molecule and the direction of the ray of light
14
a
is small. Since the transmittance of the ray of light having been transmitted through the liquid crystal depends upon the included angle defined by the longitudinal axis of the liquid crystal molecule and the direction of the ray of light
14
b
, the transmittance of the ray of light
14
b
through the liquid crystal is high. Accordingly, if the observer views the screen in the direction of an arrow mark
13
b
in parallel to the ray of light
14
b
, then the transmittance of the ray of light
14
b
through the liquid crystal is high. As described above, the nematic or twisted nematic liquid crystal display has the above problem in a remarkable dependency upon the view angle.
In order to settle the above problem in the remarkable dependency upon the view angle, it was proposed to divide the orientation of the twisted nematic liquid crystal molecules into two different orientations over two divided areas for the purpose of reduction in dependency upon the view angle. This technique is disclosed in Japanese laid-open patent publication No. 63-106624. Two types of areas in different two orientation directions co-exit in each pixel.
FIG. 2
is a schematic view illustrative of the twisted nematic liquid crystal molecules which are tilted and risen up in different two orientations from the substrate surface to explain the dependency upon the view angle of the twisted nematic liquid crystal molecules. Each pixel is divided into two types of the area differing in orientation by 180 degrees from each other wherein the two types of area co-exist in a local part of each pixel. The two types of the area differ in view angle dependency by 180 degrees from each other and co-exist locally in the each pixel so that the different dependencies of view angle may be canceled totally. If the observer views the screen of the display in a direction of an arrow mark
13
a
, then the rays of light
14
a
and
14
c
are taken into eyes of the observer. In this case, as well illustrated in
FIG. 2
, the ray of light
14
a
have been transmitted through the twisted nematic liquid crystal molecule
5
which is risen up toward the right-up direction and tilted from the substrate surface. Since the included angle defined by the transmission direction of the ray of light
14
a
and the longitudinal axis of the liquid crystal molecule is large, the transmittance of the ray of light
14
a
is low. In contrast, the ray of light
14
c
have been transmitted through the twisted nematic liquid crystal molecule
5
which is risen up toward the left-up direction and tilted from the substrate surface. Since the included angle defined by the transmission direction of the ray of light
14
c
and the longitudinal axis of the liquid crystal molecule is small, the transmittance of the ray of light
14
c
is high. Since the observer can view both the rays of light
14
a
and
14
c
having low and high transmittances, the dependency of the view angle is apparently reduced.
On the other hand, if the observer views the screen of the display in a different direction of an arrow mark
13
b
, then the rays of light
14
b
and
14
d
are taken into eyes of the observer. In this case, as well illustrated in
FIG. 2
, the ray of light
14
b
have been transmitted through the twisted nematic liquid crystal molecule
5
which is risen up toward the right-up direction and tilted from the substrate surface. Since the included angle defined by the transmission direction of the ray of light
14
b
and the longitudinal axis of the liquid crystal molecule is small, the transmittance of the ray of light
14
b
is high. In contrast, the ray of light
14
d
have been transmitted through the twisted nematic liquid crystal molecule
5
which is risen up toward the left-up direction and tilted from the substrate surface. Since the included angle defined by the transmission direction of the ray of light
14
d
and the longitudinal axis of the
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