Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2004-01-09
2004-12-28
Nguyen, Dung T. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S118000, C349S179000
Reexamination Certificate
active
06836306
ABSTRACT:
TECHNICAL FIELD
The present invention relates to transflective liquid crystal display devices and more specifically to improvement of such devices for achieving enhanced display quality.
BACKGROUND ART
Liquid crystal display devices have become widely spread in recent years because of their advantages such as the ability to make thinner devices and offer lower power consumption than display devices that utilize cathode ray tubes.
Liquid crystal display devices are generally divided into two types: a transmissive type and a reflective type.
The transmissive liquid crystal display device utilizes light irradiated from a so-called backlight to provide a display and is widely used as the display for word processors, notebook personal computers and the like. When the transmissive liquid crystal display device is utilized in environments where the intensity of incident light on the device is high, such as the outdoors, it is difficult to observe a normal display.
The reflective liquid crystal display device reflects outside light and utilizes the light to provide a display and thus does not have a backlight, which, in turn, offers lower power consumption than the transmissive type. Accordingly, with the rapid spread of portable equipment, the reflective liquid crystal display device is receiving wide attention as the display for such equipment. The reflective liquid crystal display device is capable of providing a satisfactory display in environments with strong outside light, such as the outdoors, but incapable of providing a normal display in environments where the intensity of incident light on the device is low, such as nighttime.
Hence, a so-called transflective liquid crystal display device having the functions of both the transmissive and reflective liquid crystal display devices is receiving attention. For example, Japanese Unexamined Patent Publication No. 7-318929 suggests a liquid crystal display device that utilizes a substrate having a transflective reflecting film on the rear side thereof. In addition, Japanese Unexamined Patent Publication No. 11-109417 suggests a liquid crystal display device having pixels which include both transmissive and reflective electrodes.
The transflective liquid crystal display device exhibits excellent visibility regardless of the brightness of the environment in which it is used, but on the other hand, the device has lower brightness than the transmissive and reflective liquid crystal display devices and is lack of the colorfulness of the image. For example, in a transflective liquid crystal display device having both transmissive and reflective electrodes, by increasing the ratio of the area occupied by the reflective electrodes and increasing the intensity of the backlight, the display brightness can be increased both in a reflective display mode and in a transmissive display mode. These measures, however, contribute to an increase in the amount of power consumption in the transmissive display mode, resulting in the loss of the advantage of low power consumption provided by the liquid crystal display device.
Furthermore, as is suggested in the above publication, in a display mode such that the backlight is driven all the time and a reflective display is complemented by a transmissive display, an excellent image display can be realized even in bright environments but a power consumption equal to or higher than that of the transmissive liquid crystal display device is required. That is, this leads to the loss of the advantage of low power consumption provided by the reflective display mode.
While in the transmissive display mode, light irradiated from the backlight is transmitted through the liquid crystal layer only once, in the reflective display mode, incident light is transmitted though the liquid crystal layer twice, before and after reflecting at a reflecting means such as reflective electrodes. There is a demand to reduce variations in display quality due to the optical path difference between the two modes. Hence, Japanese Unexamined Patent Publication No. 11-242226 suggests a transflective liquid crystal display device in which the alignment of liquid crystal molecules in reflective display regions is different from the alignment of liquid crystal molecules in transmissive display regions. However, when, as is suggested in the above-described publication, a plurality of regions having liquid crystal molecules whose alignments vary from region to region are provided, the alignment of the liquid crystal molecules becomes discontinuous at the boundaries between the regions, resulting in formation of so-called disclination lines. The liquid crystal molecules in those regions suffer from alignment defects, ending up not contributing at all to a normal display or requiring a long period of time to obtain an intended alignment.
Moreover, as was described above, in the transmissive display mode, light irradiated from the backlight is transmitted through the color filter only once, and in the reflective display mode, incident light is transmitted through the color filter twice, before and after reflecting at a reflecting means such as reflective electrodes, and thus variations in the hue of display occur between the two modes. The above-described publication also suggests that the device provides a color display only in transmissive display portions and in reflective display portions a non-color display is provided. Specifically, color filters are provided in the transmissive display regions, and light in the reflective display portions only contributes to the pixel lightness. This technique, however, has difficulty providing a display with higher brightness because the brightness of the pixels is controlled only by the area of the transmissive display portions.
Hence, there has been a demand for transflective liquid crystal display devices capable of providing a display with higher image quality while maintaining the advantage of power-saving features provided by the liquid crystal display device.
For the liquid crystal display device, generally, an improvement in the display quality of the moving images, i.e., in response time, and an increase in viewing angle are demanded. Thus, optically compensated bend (OCB) mode liquid crystal display devices having excellent response time and viewing angle are receiving attention. In the OCB mode liquid crystal display panel, when a voltage is not applied between a pixel electrode
103
on an array substrate
102
and a counter electrode
106
on a counter substrate
105
, liquid crystal molecules
100
exhibit a splay alignment as shown in
FIG. 13
a
, and when a voltage is applied, the liquid crystal molecules exhibit a bend alignment as shown in
FIG. 13
b
. In addition, as the driving mode for the reflective liquid crystal display device, a reflective OCB (R—OCB) mode is suggested. As is shown in
FIG. 14
, in the R—OCB mode, a liquid crystal molecule on the side of one of the electrodes exhibits a hybrid alignment such that the long axis of the liquid crystal molecule is oriented perpendicular to a surface of the reflective electrode, while a liquid crystal molecule on the side of the other electrode exhibits a bend alignment.
In the transmissive liquid crystal display device, the so-called field-sequential technique, which eliminates the need to use color filters, is widely studied. For example, Japanese Unexamined Patent Publication No. 9-101497 suggests a TN mode liquid crystal display device with a backlight made up of three color tubes of R (red), G (green), and B (blue) in which each of the R, G, and B tubes is sequentially turned on at regular intervals.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a liquid crystal display device having excellent display quality and capable of precisely controlling the alignment of liquid crystal molecules and of providing a display with high brightness and high color purity both in a transmissive display mode and in a reflective display mode.
According to the present invention, there is provided a transflective liqu
Hotta Sadayoshi
Kubota Hirofumi
Uemura Tsuyoshi
Wakita Naohide
Nguyen Dung T.
Parkhurst & Wendel L.L.P.
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