Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-08-22
2003-12-16
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S119000, C349S120000
Reexamination Certificate
active
06665032
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to an optically compensated bend (OCB) mode LCD device and, more particularly, to an OCB mode LCD device having an improved contrast ratio.
(b) Description of the Related Art
LCD devices are increasingly used in recent days while replacing the conventional CRT display device due to its advantages of smaller thickness, feasibility of larger capacity for display data etc.
A twisted nematic (TN) mode is generally employed as the operational mode of the LCD device. The TN mode is such that the direction of the axes (sometimes referred to as “directors” hereinafter) of the LC molecules are twist-rotated by 90 degrees in the direction perpendicular to the substrate surface between the front substrate and the rear substrate by using a perpendicular electric field which is normal to the substrate surface.
The TN mode has a disadvantage, however, in that the resultant LCD device has a narrow viewing angle, which hinders the picture on the screen from being clearly observed in the diagonal direction with respect to the perpendicular of the screen (substrate surface). In addition, in the case of a larger screen display device, a picture element appearing on the center of the screen and another picture element appearing on the periphery of the screen provide different image characteristics as observed from a point diagonally with respect to the perpendicular of the screen, whereby a correct image display is not possible.
JP-A-6-75116 describes a TN mode LCD device wherein a phase compensating plate is provided for enlarging the viewing angle. However, even this technique cannot solve the above problem to a desired extent or sufficiently compensate the twisted structure peculiar to the TN mode LCD device.
There is another technique of interest for improving the narrow viewing angle, called OCB mode wherein a LC cell having a bend orientation arrangement (or may be a parallel orientation arrangement) is combined with a phase compensating plate. The OCB mode is especially noticed due to its higher-speed response.
FIG. 1
shows a schematic chart showing orientation arrangements of directors of the LC molecules between the substrates, including a splay orientation arrangement, a twist orientation arrangement and a bend orientation arrangement, as viewed from the left of the drawing. Of these orientation arrangements, the bend orientation arrangement has a plane symmetry structure with respect to the central plane between the substrates, wherein the directors of the LC molecules reside in a standing posture, or are normal to the substrate surface, at the central area and “falls” toward both the substrates to be parallel to the substrate surfaces in the vicinity of the substrates.
The OCB mode is achieved by providing a LC layer having a bend orientation arrangement between the substrates and a phase compensating plate or plates for compensating the phase of the LC layer.
Known techniques for using the phase compensating plate in the LC device having the bend orientation arrangement include one using a phase compensating plate having a negative birefringence as described in JP-A-6-294962, one using a bi-axial phase compensating plate as described by Kuo in SID′ 94 Digest, and one using a pair of phase compensating plates each having a negative birefringence and a hybrid orientation arrangement as described in JP-A-10-197862.
FIG. 2
shows the structure of the conventional OCB mode LCD device described in JP-A-10-197862, as mentioned above. A first substrate
21
mounts thereon either red, green or blue color filter
29
R,
29
G or
29
B for each pixel area, on which an overcoat film
13
, a common electrode
10
and a first orientation film
15
are consecutively formed.
A second substrate
22
mounts thereon a pixel electrode
27
R,
27
G and
27
B either for red, green and blue color for each pixel area, on which a second orientation film
16
is formed.
First and second substrates
21
and
22
oppose each other with a LC layer
23
being sandwiched therebetween. On the outer surface of the first substrate
21
, a first phase compensating plate
24
and a first polarizing plate
11
are consecutively formed. On the outer surface of the second substrate
22
, a second phase compensating plate
25
and a second polarizing plate
12
are consecutively formed.
FIG. 3
shows orientations of the LC layer together with the axes of the polarizing plates
11
and
12
and the phase compensating plates
24
and
25
, as viewed from the first substrate side.
FIG. 4
shows schematic sectional view depicting the directors or the LC molecules and birefringences of the phase compensating plates as well as birefringence eclipses of the LC layer and the phase compensating plates during displaying a black color, wherein “ne” denotes the abnormal optical axis and “no” denotes a normal optical axis.
In
FIG. 3
, the orientations
101
and
102
of the first and second orientation films are formed in the same direction as the inclined directions
201
and
202
of the birefringences of the phase compensating plates so that the abnormal optical axis “ne” of the LC layer resides in the same direction as the abnormal optical axis “ne” of the birefringence of the phase compensating plates.
The polarizing axis
301
of the first polarizing plate is set at 45 degrees away from the orientation
101
of the first orientation film, and the polarizing axis
302
of the second polarizing plate is set at 90 degrees away from the polarizing axis of the first polarizing plate.
In
FIG. 4
, symbols LC
1
to LC
5
show a birefringence eclipse at the respective divided planes of the LC layer divided into ten layers, whereas symbols RF
1
to RF
5
show a birefringence eclipse at the respective divided planes of the phase compensating plate divided into five layers. In this example, it is assumed for simplicity that each layer has an equal thickness.
The longer axis of the birefringence LC
1
in the central area of the LC layer is normal to the substrate surface, and the longer axis of the birefringence LC
5
of the LC layer in the vicinity of the orientation layer is parallel to the substrate surface, with the axes of the birefringences having intermediate numbers LC
2
, LC
3
, LC
4
resides between those directions. On the other hand, the longer axis of the birefringence RF
1
of the phase compensating plate at the outer surface thereof is normal to the substrate surface and the longer axis of the birefringence RF
5
at the inner surface is parallel to the substrate surface.
The negative birefringence of the phase compensating plate oriented in a hybrid orientation arrangement corresponds to the birefringence of the LC layer when the LC layer displays a black color. The birefringences LC
1
, LC
2
, . . . , LC
5
of the LC layer correspond to the birefringences RF
1
, RF
2
, . . . , RF
5
, respectively, of the phase compensating plate for effecting compensation of retardation.
The overall retardation “R” of the LCD device can be expressed by equation (1) based on the refractive indices and the thicknesses of the LC layer and the phase compensating plate:
R=Rlc+Rrf
=[(
nlcx×dlc+nrfx×drf
)−(
nlcy×dlc+nrfy×drf
)] (1)
wherein nlcx, nlcy, nrfx and nrfy are the refractive indices of the LC layer in x-direction, the LC layer in y-direction, the phase compensating plate in x-direction and the phase compensating plate in y-direction, respectively, all of these being observed from a single point, and wherein dlc and drf are the thicknesses of the LC layer and the phase compensating plate, respectively.
Rlc and Rrf are retardations of the LC layer and the phase compensating plate, and are expressed by;
Rlc
=(
nlcx−nlcy
)×
dlc
, and
Rrf
=(
nrfx−nrfy
)×
drf.
If the birefringences LC
5
and RF
5
, for example, are observed from the front, birefringence LC
5
has a larger refractive index in x-direction whereas birefringence RF
5
has a l
Chung David
Hayes & Soloway P.C.
NEC Corporation
Ton Toan
LandOfFree
Optically compensated bend mode LCD device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optically compensated bend mode LCD device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optically compensated bend mode LCD device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3176020