Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2003-05-02
2004-10-05
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S180000, C349S121000
Reexamination Certificate
active
06801283
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device having a reflective liquid crystal display element, such as a reflective liquid crystal display device and a transflective liquid crystal display device including a reflective liquid crystal display element and a transmissive liquid crystal display element.
2. Description of Related Art
Being thin, lightweight, and low power consumption, a liquid crystal display device is widely used as a portable device display. Since the liquid crystal display device is not a light emitting element, it requires an external light source. Depending on the type of the external light source, the liquid crystal display device is divided roughly into two categories: transmissive-type and reflective-type.
A transmissive liquid crystal display device has a backlight using an light emitting element such as a cold-cathode fluorescent lamp and LED mounted behind the device, that is, the opposite to the side of an observer. The light from the backlight is modulated by a liquid crystal panel, thereby displaying images. On the other hand, a reflective liquid crystal display device uses a light source on the observer's side such as sunlight as the external light source. The light is reflected by a reflector mounted opposite to the observer, and the reflected light coming back to the observer's side is modulated by a liquid crystal panel, thereby displaying images.
However, the transmissive type has the problem of dim display in bright ambient light, and the reflective type has the problem of dark display in low ambient light. As a solution to the above problem, a “transflective” liquid crystal display device having display areas of both reflective-type and transmissive-type in one pixel area has been proposed. The transflective liquid crystal display device is described in Japanese Patent Application Laid-Open No. 2000-187220, for example. The transflective liquid crystal display device serves as a reflective-type with backlight off in bright ambient light to provide brighter images and reduce power consumption, while serves as a transmissive-type with the backlight on in low ambient light to provide brighter and higher-quality images. Therefore, the transflective liquid crystal display device is widely used as a cellular phone display.
FIG. 1
shows a configuration example of the transflective liquid crystal display device described in Japanese Patent Application Laid-Open No. 2000-187220. As shown in
FIG. 1
, the transflective liquid crystal display device has a circular polarizer
11
and a substrate
21
a
above liquid crystal layers
22
and
23
. The circular polarizer
11
is a composite structures consisting of a polarizer
1
, a retarder
2
, and a retarder
3
. The retarder
3
produces approximately half the retardation of the retarder
2
. The substrate
21
a
has a transparent electrode to apply a voltage to the liquid crystal layers.
The liquid crystal layers
22
and
23
are sandwiched between substrates
21
a
and
21
b
, having different retardations. A reflective section further has a reflector
31
reflecting light in a visible light range. Between the reflector
31
and the substrate
21
b
is an organic layer. A transmissive section, on the other hand, has a transparent electrode to applying a voltage to the liquid crystal layer on the substrate
21
b.
Below the liquid crystal layers
22
and
23
are provided the substrate
21
b
and a circular polarizer
12
. The circular polarizer
12
is a composite structure consisting of a polarizer
4
, a retarder
5
, and a retarder
6
. The retarder
6
produces approximately half the retardation of the retarder
5
.
As described above, the transflective liquid crystal display device has a reflective liquid crystal display element in the reflective section, and a transmissive liquid crystal display element in the transmissive section, both in one pixel area. The reflective liquid crystal display element is configured in the order of the circular polarizer
11
(polarizer
1
, retarder
2
, and retarder
3
), substrate
21
a
, liquid crystal layer
22
, reflector
31
, and substrate
21
b
, or in the order of the circular polarizer
11
(polarizer
1
, retarder
2
, and retarder
3
), substrate
21
a
, liquid crystal layer
22
, substrate
21
b
, and reflector
31
. On the other hand, the transmissive liquid crystal element is configured in the order of the circular polarizer
11
(polarizer
1
, retarder
2
, retarder
3
), substrate
21
a
, liquid crystal layer
23
, substrate
21
b
, and circular polarizer
12
(retarder
6
, retarder
5
, and retarder
4
).
When the angle between a transmission axis of the polarizer
1
and a slow axis of the retarder
2
is &thgr;1, the angle between the slow axis of the retarder
2
and a slow axis of the retarder
3
is &thgr;1+45 degrees. Further, when the retarder
2
produces approximately half wavelength of retardation, and the retarder
3
does approximately quarter wavelength of retardation, the composite of the polarizer
1
, retarder
2
, and retarder
3
serves as the circular polarizer
11
for the subject wavelength. The subject wavelength is generally 550 nm. The retarder producing half wavelength of retardation is called a half wave retarder, and the retarder producing quarter wavelength of retardation, a quarter wave retarder. Similarly, the composite of the polarizer
4
, retarder
5
, and the retarder
6
serves as the circular polarizer
12
. The multilayer circular polarizers
11
and
12
composed of the half wave retarder and quarter wave retarder are especially called wide-band circular polarizers since circularly polarized light can be obtained in a wide wavelength range.
A coordinate system will be explained hereinbelow with reference to
FIG. 2
to clarify the directions of the polarizer and retarder. The following descriptions use a right-handed coordinate system where the direction from the backlight toward the polarizer
1
is the positive direction of z-axis. When a transmission axis of the polarizer
1
is &agr;1, a slow axis of the retarder
2
is &agr;2, and a slow axis of the retarder
3
is &agr;3, the axis of the polarizer, half wave retarder, and quarter wave retarder constituting the wide-band circular polarizer have the relation: &thgr;1=(&agr;2−&agr;1) and (&agr;3−&agr;2)=(&thgr;1+45 degrees).
FIG. 3
schematically illustrates display principle of a transflective liquid crystal display device using a circular polarizer. First, a white display with high reflectivity and transmissivity will be explained. In the reflective section, the liquid crystal layer
22
has such a thickness as to produce quarter wavelength of retardation. In this configuration, as the circularly polarized light having passed through the circular polarizer
11
enters the liquid crystal layer
22
, it is converted to linearly polarized light just before the reflector
31
. After reflected by the reflector
31
, the light returns, passing through the liquid crystal layer
22
again, changing into the circularly polarized light having a different chirality. Therefore, the reflected light can pass through the circular polarizer
11
, achieving a bright white display.
In the transmissive section, on the other hand, the liquid crystal layer
23
has such a thickness as to produce half wavelength of effective retardation. In this configuration, as the circularly polarized light having passed through the circular polarizer
12
enters the liquid crystal layer
23
, it is converted to the circularly polarized light having a different chirality just before the substrate
21
a
. Therefore, the light having passed through the liquid crystal layer can pass through the circular polarizer
11
, achieving a bright white display.
If a voltage is applied to the liquid crystal layer, liquid crystal molecules stand up, reducing effective retardation of the liquid crystal layer. For simplifying the principle explanation, the effective retardation of
Koyama Hitoshi
Kurata Tetsuyuki
Nishioka Takahiro
Satake Tetsuya
Advanced Display Inc.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Parker Kenneth
LandOfFree
Liquid crystal display 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 Liquid crystal display device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid crystal display device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3303397