Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-10-22
2004-09-14
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S119000
Reexamination Certificate
active
06791640
ABSTRACT:
TECHNICAL FIELD
The present invention relates to reflective liquid crystal display devices for direct view application used in wordprocessors, laptop personal computers, and other office machinery, as well as in a variety of visual and game machines, without a need for a backlight, and also relates to such reflective liquid crystal display devices incorporating a touch panel arranged therefrom.
BACKGROUND ART
Liquid crystal display devices, being characterized by their thinness and light weight, have successfully found commercial applications as color display devices. Among these color liquid crystal display devices, transmissive liquid crystal display devices provided with a light source for illumination from behind are in particularly widespread use, and are adopted for an increasingly wider variety of applications because of the above-mentioned features.
In contrast to the transmission liquid crystal display device, the reflective liquid crystal display device does not require a backlight for display, and therefore can reduce the power consumption of the light source. The exclusion of the backlight further characterizes the reflective liquid crystal display device by allowing it to be more compact and lightweight.
In other words, in comparison to conventional transmissive liquid crystal display, the reflective liquid crystal display device can lower the power consumption, and be suitably used in equipment which needs to be lightweight and thin. For example, if the equipment with the reflective liquid crystal display device is designed while retaining conventional operation time, the reflective liquid crystal display device can not only cut down on the backlight space and weight, but consumes less power, and becomes capable of running on a smaller battery, making it possible to further reduce the size and weight. If the equipment with the reflective liquid crystal display device is manufactured while retaining conventional size or weight, use of a larger battery is expected to increase operation time dramatically.
In addition, as to display contrast properties, the light emitting display device, such as the CRT, degrades greatly in contrast ratio when used outdoors during the daytime. Even the transmissive liquid crystal display device subjected to a low reflection treatment inevitably suffers similarly from greatly decreased contrast ratios when used in ambient light, such as direct sunlight, that is excessively strong compared to display light.
In contrast, with the reflective liquid crystal display device, the display light obtained is proportional to the amount of ambient light, which is an especially suitable feature for application in a personal digital tool, a digital still camera, a portable camcorder, and other devices that are often used outdoors.
When considering these potential application fields, the reflective color liquid crystal display device appears very promising; however, a relatively low contrast ratio and reflectance, as well as insufficient performances in multi-color, high precision, and moving picture display, have so far been obstacles in realizing commercially viable reflective color liquid crystal display device.
The following description will explain the reflective liquid crystal display device in further detail. The conventional twisted nematic (TN) type liquid crystal element includes two linear polarizer plates (hereinafter, will be simply referred to as polarizer plates), and therefore boasts an excellent contrast ratio and viewing angle dependency property; however, the reflectance is inevitably low. In addition, since the liquid crystal modulation layer is separated from the light reflective layer by a distance equivalent to the thickness of a substrate, etc., there occurs parallax due to a disparity between incoming and outgoing optical paths of illumination light. Therefore, especially in a typical arrangement used for transmissive liquid crystal display devices where a single liquid crystal modulation layer is combined with a color filter that includes a separate subpixel for each color element, provided that light does not travel parallel to the normal to the substrate, ambient light enters and exits after reflection through different color subpixels. This causes moire and other undesirable phenomena, rendering the transmissive liquid crystal display device unsuited for high resolution, high precision, color display use.
For these reasons, no reflective color display device using this display mode has so far been commercialized.
Meanwhile, Guest-Host type liquid crystal elements (hereinafter, will be abbreviated as GH) have been developed that uses no or only one polarizer plate and includes liquid crystalline material doped with dyestuff. However, the GH type liquid crystal element is not highly reliable due to the addition of the dye, and the low dichroic ratio of the dye cannot produce a high contrast ratio.
Among these problems, the insufficient contrast level in particular causes serious degradation in color purity and creates a need to incorporate a color filter of high color purity in a color display device using a color filter. This entails a problem of reduced brightness caused by the color filter of high color purity, and cancels to some degree the advantage of this mode that high brightness is achieved by use of no polarizer plates.
On these backgrounds, research and development is under way to successfully manufacture a liquid crystal display element in a mode in which a single polarizer plate is used (hereinafter, will be referred to as a single polarizer plate mode), which is highly promising to realize a high resolution and high contrast display.
Japanese Laid-Open Patent Application No. 55-48733/1980 (Tokukaisho 55-48733) discloses such an example of a liquid crystal display element of a reflective TN mode (45°-twisted type) using a single polarizer plate and a quarter-wave plate.
With this liquid crystal display device, black and white display is performed, using a 45°-twisted liquid crystal layer and controlling the electric field applied thereacross, by realizing two states, in one of which the plane of polarization of incoming linearly polarized incident light is parallel to the optical axis of the quarter-wave plate and in the other of which the plane of polarization forms 45° with the optical axis of the quarter wave plate. The liquid crystal cell is structured to include a polarizer, a 45°-twisted liquid crystal cell, a quarter-wave plate, and a reflector plate, when viewed from the side at which light enters.
Further, U.S. Pat. No. 4,701,028 (Clerc et al.) discloses a liquid crystal display device of a reflective-type, homeotropic alignment mode wherein a combination of a single polarizer plate, a quarter-wave plate, and a perpendicularly aligned liquid crystal cell is used.
Meanwhile, the inventors of the present application filed an application for a reflective-type, parallel alignment mode wherein a combination of a single polarizer plate, a homogeneous alignment liquid crystal cell, and an optical retardation compensation plate is used (see Japanese Laid-Open Patent Application No. 6-167708/1994 (Tokukaihei 6-167708)).
This reflective liquid crystal display device includes a liquid crystal cell constituted by a homogeneously-aligned liquid crystal layer, a reflector plate (disposed inside the liquid crystal cell beneath the liquid crystal layer), a polarizer plate (disposed on the liquid crystal cell), and a single optical retardation compensator plate (placed between the liquid crystal cell and the polarizer plate). Further, according to this display mode, throughout the total length of the optical path, i.e., the incoming optical path and the outgoing optical path, light passes through the polarizer plate only twice and through the transparent electrode where light is inevitably absorbed on a glass substrate (top substrate) of the liquid crystal cell also only twice. Therefore, a high reflectance can be obtained by means of a reflective liquid crystal display device of this structure.
Further, Japanese Lai
Mitsui Seiichi
Okamoto Masayuki
Satoh Takashi
Birch & Stewart Kolasch & Birch, LLP
Chowdhury Tarifur R.
Chung David
Sharp Kabushiki Kaisha
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