Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-04-09
2004-02-24
Flynn, Nathan J. (Department: 2826)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S114000, C349S121000, C349S117000, C349S122000, C349S072000, C349S082000
Reexamination Certificate
active
06697137
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semi-transmission/reflection-type liquid crystal display device that displays an image by selectively using transmission light and reflection light.
Being thin, light, and low in power consumption, liquid crystal display devices in which a liquid crystal display panel is used as an image generating means are employed as display devices in a wide variety of electronic equipment, such as notebook-sized personal computers, word processors, electronic notes, cellular phones, and camera-incorporated video recorders.
In contrast to CRTs and plasma display panels, liquid crystal display panels display an image by controlling the quantity of light that has entered the panel from the outside instead of emitting light by itself. When equipped with color filters of plural colors as light control elements, liquid crystal display panels can display a color image of multiple colors.
Liquid crystal display devices that are used most commonly at present are transmission-type devices in which an illumination light source, called a backlight that uses a fluorescent tube, is provided on the back side of a liquid crystal panel, and an image is displayed by controlling the quantity of light (part of light emitted from the backlight) that passes through the liquid crystal panel.
However, in such transmission-type liquid crystal display devices, the power consumption of the backlight accounts for approximately one half of the total power consumption. This is a major factor in shortening the usable time in a case where portable electronic apparatuses as exemplified above are of a battery-driven type. Transmission-type liquid crystal display devices have another problem, in that, when they are used in a bright outdoor environment, for example, ambient light is reflected by the surface of the display area and a displayed image becomes hard to recognize.
Among liquid crystal display devices that are always used in a carried state in a bright environment such as found outdoors, there are reflection type liquid crystal display devices that usually do not use a backlight, but are equipped with a reflection plate, and control the quantity of reflection light (part of ambient light) with the liquid crystal layer. An example of such liquid crystal display devices is one that performs both transmission-type display and reflection-type display using a semitransparent reflecting film (e.g., Japanese Unexamined Patent Publication No. Hei. 7-333598).
Another example of the above type of liquid crystal display device is one in which each pixel electrode is composed of two regions that comprise a reflection region and a transmission region (e.g., Japanese Unexamined Patent Publication No. Hei. 7-333598).
However, in the above conventional liquid crystal display devices, the display quality varies depending on the use environment (light-source-related environment). That is, a display that is performed by using reflection light (reflection light mode) and a display that is performed by using transmission light (transmission light mode) having different contrast ratios. Further, a coloration phenomenon may occur in black-and-white display and hue deviation may occur in color display. The difference in contrast ratio is caused by the fact that the black display luminance (off transmittance) and the white display luminance (on transmittance) are different between the case where reflection light is used and the case where transmission light is used. This phenomenon lowers the legibility of a displayed image. The hue deviation is a phenomenon that the hue shifts to the bluish side particularly in the case where transmission light is used. This deteriorates the color reproduction performance.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above problems in the art, and an object of the invention is therefore to provide a liquid crystal display device which is capable of image display with a large contrast ratio in both a transmission display mode and a reflection display mode, as well as being capable of good color display in both display modes.
To attain the above object, the invention provides the following configuration. A liquid crystal is interposed between a first transparent substrate having first electrodes and a second transparent substrate having other electrodes that are opposed to the first electrodes. Pixel regions are formed at portions where the first electrodes and the other electrodes are opposed to each other. A semitransparent reflecting film (or an opaque reflecting film) is formed between the first transparent substrate and the first electrodes. The semitransparent reflecting film is formed with light transmission apertures in each pixel region. Or, the semitransparent reflecting film is formed with slits at positions corresponding to the gaps between adjacent pixel regions. With the above measure, part of the illumination light that comes from the first transparent substrate side is introduced to the liquid crystal through the light transmission apertures or the slits.
An opaque reflecting film may be formed instead of a semitransparent reflecting film. In the case of an opaque reflecting film, the combination of the opaque reflecting film and the light transmission apertures serves as the above-mentioned “semitransparent reflecting film.” In the case of the semitransparent reflecting film, the semitransparent reflecting film itself and the light transmission apertures serve as the above-mentioned “semitransparent reflecting film.” The same interpretation applies to the term “semitransparent reflecting film” that will be used in the following description and embodiments.
With the above configuration, in the transmission light mode, part of the light that comes from the outside of the first transparent substrate is output from the second transparent substrate after passing through color filters. Therefore, not only is the legibility of a display image improved, but also a hue deviation in transmission light is decreased, which improves the color reproduction performance.
Where the semitransparent reflecting film also occupies the portions corresponding to the gaps between the adjacent pixel regions, the contrast in the transmission light mode is increased.
The peripheral portions of adjacent ones of color filter layers that are formed between the second transparent substrate and the other electrodes may overlap with each other to provide a light shield function. Since the overlapping portions of the color filter layers serve as light shield layers, the contrast is increased.
A light absorption film may be formed under the slits that are formed on the side of the first transparent substrate, or the slits may be charged with a light absorption film. This prevents color mixture between adjacent pixels and hence increases the contrast.
A semi-transmission/reflection-type liquid crystal display device is constructed by disposing an illumination light source on the back side of the first transparent substrate of the above liquid crystal display panel. In an environment where the brightness is sufficiently high, the semi-transmission/reflection-type liquid crystal display device is used in the reflection light mode by turning off the illumination light source. In a dark environment, it is used in the transmission light mode by turning on the illumination light source. The color reproduction performance is improved in either mode.
In the semi-transmission/reflection-type liquid crystal display device using the above liquid crystal display panel, an upper polarizer and a lower polarizer are formed on the display screen side (i.e., the second transparent substrate side) of the liquid crystal display panel and on the side opposite to it (i.e., the first transparent substrate side), respectively, and their optical absorption axes (polarizing axes) are set approximately perpendicular to each other.
A first alignment layer is formed on the inside surface of the substrate (first transparent substrate) provided on the illuminatio
Fujieda Masayoshi
Hiraga Koji
Hoshino Noboru
Nakamura Yoshiaki
Nemoto Souta
Antonelli Terry Stout & Kraus LLP
Erdem Fazli
Flynn Nathan J.
Hitachi , Ltd.
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