Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-10-04
2003-09-30
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S139000, C349S143000
Reexamination Certificate
active
06628357
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to the technical field of liquid crystal devices. In particular, the present invention relates to a structure of a liquid crystal device which can change a display mode between a reflective mode and a transmissive mode, and to an electronic device using the liquid crystal device.
2. Background Art
Reflective liquid crystal devices consuming small amounts of electrical power have been widely used in portable devices and display sections in various apparatuses. Since, however, the display is performed by external light, an image is not visible in dark environments. Thus, some proposed liquid crystal devices use external light in a lighted environment as in general reflective liquid crystal devices, and an internal light source in dark environments so as to maintain a visible state. As disclosed in Japanese Patent Application Laid-Open Nos. 57-049271, 57-049271, and 57-049271, each device has a polarizer, a transflector, and a backlight, in that order, at the outer face, away from the viewer, in a liquid crystal panel. The liquid crystal device performs reflective display using external light reflected by the transflector in a lighted environment, and transmissive display using light from the backlight, which is turned on so as to maintain a visible state, transmitted through the transflector in dark environments.
Another liquid crystal device having improved brightness in a reflective display mode is disclosed in Japanese Patent Application Laid-Open No. 8-292413. The liquid crystal device has a transflector, a polarizer, and a backlight, in that order, at the outer face, away from the viewer, of the liquid crystal panel. The device performs reflective display using external light reflected by the transflector when the environment is light, and transmissive display using light from the backlight, which is turned on so as to maintain a visible state, transmitted through the polarizer and the transflector. Since the polarizer is not provided between the liquid crystal cell and the transflector, brighter display is achieved in a reflective mode compared to the above-mentioned liquid crystal devices.
In the liquid crystal device disclosed in Japanese Patent Application Laid-Open No. 8-292413, however, a transparent substrate is disposed between a liquid crystal layer and the transflector; hence, problems, such as double imaging and blurred imaging, occur.
Color liquid crystal display has been required with recent development of portable devices and office automation devices. Apparatuses using reflective liquid crystal devices also require color display. In a combination of the liquid crystal device disclosed in the above patent application with a color filter, the transflector is arranged behind the liquid crystal panel. Thus, the thick transparent substrate lies between the liquid crystal layer with the color filter and the transflector, resulting in occurrence of double imaging or blurred imaging due to parallax and insufficient coloring.
In order to solve the problems, Japanese Patent Application Laid-Open No. 9-258219 discloses a reflective color liquid crystal device in which a reflector is disposed so as to come into contact with the liquid crystal layer. This liquid crystal device, however, cannot display visible images in dark environments.
In addition, Japanese Patent Application Laid-Open No. 7-318929 discloses a transflective liquid crystal device in which a pixel electrode functioning as a transflective film is provided on the inner face of the liquid crystal cell. Since this liquid crystal device has a transflective film such as a metallic thin film having fine defects including pinholes, dimples, and fine openings, an oblique electric field which is generated on the periphery of the defects and openings causes unsatisfactory orientation of the liquid crystal, producing many technical problems which inhibit high-quality image display. That is, a high contrast and brightness are not achieved, and coloring due to wavelength dispersion of light inevitably occurs both in a reflective display mode and a transmissive display mode. Furthermore, it is difficult to achieve both prevention of brightness defects at the gap between pixel electrodes or an improvement in contrast and an improvement in brightness in a reflective display mode. Furthermore, the production process requires addition of a particular step; hence, the device satisfies with great difficulty a typical demand for reduction in production cost in this technical field.
The present invention has been accomplished in view of the above-mentioned problems and has an object to provide a transflective liquid crystal device, which is changeably used both in a reflective display mode and a transmissive display mode, does not produce double imaging and blurred imaging due to parallax, can display high-quality images, and to provide an electronic apparatus using the liquid crystal device.
SUMMARY OF THE INVENTION
The object of the present invention is achieved by a first liquid crystal device including a pair of first and second transparent substrates; a liquid crystal layer disposed between the first and second substrates; a transparent electrode formed on a face of the first substrate on the side of the liquid crystal layer; a reflective electrode formed on a face of the second substrate and having an oblong slit, the face contacting the liquid crystal layer; and an illumination unit provided on another face of the second substrate on the opposite side of the liquid crystal layer.
In accordance with the first liquid crystal device of the present invention, the reflective electrode reflects external light incident on the first substrate towards the liquid crystal layer in a reflective display mode. Since the reflective electrode is provided on the liquid crystal layer face of the second substrate, no gap is substantially formed between the liquid crystal layer and the reflective electrode and thus double imaging and blurred imaging due to parallax do not occur. In a transmissive display mode, illuminated light incident on the second substrate from the illumination unit enters the liquid crystal layer through the slits. Thus, the illuminated light enables bright display in dark environments.
Since the reflective electrode has oblong slits, an oblique electric field (hereinafter referred to as an “oblique electric field due to the short sides of the slit”) is applied to the liquid crystal layer between the edges of each reflective electrode defining short sides of a slit and opposingly disposed at a relatively large distance (edges of each reflective electrode opposing each other at each end of two long sides of a slit) and the transparent electrode. An oblique electric field (hereinafter referred to as an “oblique electric field due to the long sides of the slit”) is simultaneously applied to the liquid crystal layer between edges of each reflective electrode defining long sides of a slit and opposingly disposed at a relatively short distance (edges of each reflective electrode opposing each other at each end of two short sides of a slit) and the transparent electrode. The components of the oblique electric field due to the short sides of the slit and the same of the oblique electric field due to the long sides of the slit are perpendicular to each other in the substrate plane. When these two oblique electric fields interact with liquid crystal molecules in the vicinity of the slit, the intensities of these two oblique electric fields determine the direction of movement of liquid crystal molecules. If the slit is a square, these two oblique electric fields are equivalent to each other. Thus, the relationship between these intensities is reversed at some positions. As a result, the directions of movement of liquid crystal molecules are different at these positions, and insufficient alignment of the liquid crystal appears as a relatively large domain. That is, display defects occur in the domain. Insufficient alignment is most noticeable when these
Maeda Tsuyoshi
Okamoto Eiji
Okumura Osamu
Seki Takumi
Chung David
Harness & Dickey & Pierce P.L.C.
Kim Robert H.
Seiko Epson Corporation
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