Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-12-27
2004-07-20
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S114000
Reexamination Certificate
active
06765638
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a liquid crystal device, such as a reflective liquid crystal device, a transflective liquid crystal device, or the like, using a passive-matrix, an active-matrix or a segmented driving system, and to electronic equipment using the liquid crystal device. Particularly, the present invention relates to a liquid crystal device which employs an internal reflection system including a reflecting electrode serving as a reflector or transflector which is provided on the side of a substrate which faces a liquid crystal, and to electronic equipment using the same.
2. Description of Related Art
A reflective liquid crystal device using external light, and not a light source, such as a back-light, or the like, for display is advantageous from the viewpoints of low power consumption, miniaturization, weight reduction, etc., and is conventionally used for portable electronic equipment, such as portable telephones, wristwatches, electronic notebooks, notebook-type personal computers, and the like, in which, particularly, portability is regarded as important. A conventional reflective liquid crystal device includes a transmissive liquid crystal panel composed of a liquid crystal held between a pair of substrates, a reflector attached to the back of the transmissive liquid crystal panel so that external light incident on the front side is reflected by the reflector through the transmissive liquid crystal panel, a polarizer, etc. However, this device has a long optical path from the liquid crystal isolated by the substrates to the reflector, and thus causes parallax in a display image, causing double display. The conventional reflective liquid crystal device is thus unsuitable for high-definition image display, and it is very difficult to display a high-quality image, particularly in color display, because colors are mixed in the above-described long optical path. Furthermore, since external light is attenuated during the time from incidence on the liquid crystal panel to reflection by the reflector, it is difficult for the liquid crystal device to perform bright display.
Therefore, a reflective liquid crystal device having an internal reflection system has recently been developed, in which a display electrode arranged on one of a pair of substrates, which is opposite to the external light incidence side, includes a reflector so as to bring the reflection position near the liquid crystal layer. As an example of such a liquid crystal device, Japanese Unexamined Patent Publication No. 8-114799 discloses a technique including forming pixel electrodes serving as reflectors on a substrate, laminating two films including a high-refractive index layer and a low-refractive index layer, or alternately laminating the films in layers, and forming an alignment layer thereon. In this technique, a multilayer film, including a high refractive index layer and a low refractive index layer, is provided on the reflectors to increase the reflectance of external light incident on the counter substrate side, thereby achieving a bright reflective display.
In the technical field of this type of liquid crystal device, under the general demand for increasing the quality of display images, and decreasing cost, it is very important to simplify the construction of the device and the manufacturing process while improving the brightness and definition of a displayed image.
However, in order to obtain high reflectance, the above-mentioned technique, in which the pixel electrodes also serve as reflectors, requires a multilayer film of at least two layers including a high refractive index layer and a low refractive index layer, which are provided on the pixel electrodes, and thus has the problem of complicating the multilayer film structure and, by extension, the construction and manufacturing process of the device.
SUMMARY OF THE INVENTION
The present invention has been achieved in consideration of the above problem and it is one aspect of the present invention to provide a reflective or transflective liquid crystal device which permits simplification of the construction and manufacturing process of the device, and which can display a high-quality bright image. The liquid crystal device may also be used in a plurality of electronic equipment.
In order to solve the above problem, a liquid crystal device of the present invention may include a first substrate, a transmissive second substrate provided to oppose the first substrate, a liquid crystal held between the first and second substrates, a reflecting electrode arranged on the side of the first substrate, which is opposite to the second substrate, a transmissive insulating film having a single-layer structure provided on the reflecting electrode d an alignment layer provided on the transmissive insulating film. The refractive index of the transmissive insulating film is set to a value lower than the refractive index of the liquid crystal and the refractive index of the alignment layer, and the width of the transmissive insulating film is set to be not less than a first predetermined width with which reflectance of a multilayer film including the reflecting electrode, the transmissive insulating film, and the alignment layer is at a maximum for blue light incident on the second substrate side, and not more than a second predetermined width with which reflectance of the multilayer film is at maximum for red light incident on the second substrate side. In the present invention, the refractive index of the liquid crystal is defined as the average of the extraordinary refractive index n
e
and the ordinary refractive index n
0
of the liquid crystal.
In the liquid crystal device of the present invention, external light incident on the second substrate side is reflected by the multilayer film including the reflecting electrode, the transmissive insulating film, and the alignment layer, which are provided on the first substrate, through the transmissive second substrate and the liquid crystal, and is again emitted from the second substrate side through the liquid crystal and the second substrate. Therefore, for example, when a polarizer is arranged on the outer side of the second substrate, the strength of external light reflected by the reflecting electrode and emitted as display light through the liquid crystal can be controlled by controlling the alignment state of the liquid crystal using the reflecting electrode, i.e., an image can be displayed according to the image signal supplied to the reflecting electrode.
The external light reflectance of the multilayer film including the reflecting electrode, the transmissive insulating film, and the alignment layer provided on the first substrate adjacent to the liquid crystal is dependent on the wavelength and varies depending upon the refractive index of the transmissive insulating film. More specifically, it is found that with the refractive index of the transmissive insulating film lower than the refractive index of the liquid crystal and the reflective index of the alignment layer, the reflectance of the multilayer film for any of red light, blue light and green light, which together form white external light, is high. Therefore, in the present invention, the refractive index of the transmissive insulating film is set to be lower than the refractive index of the liquid crystal and the refractive index of the alignment layer.
The external light reflectance of the multilayer film including the reflecting electrode, the transmissive insulating film, and the alignment layer provided on the first substrate adjacent to the liquid crystal is dependent on the wavelength and varies depending upon the width of the transmissive insulating film. More specifically, it is found that the maximum reflectance occurs for blue light (i.e., electromagnetic waves at a wavelength of about 450 nm) with the transmissive insulating film having a relatively small width, and the maximum reflectance occurs for red light (i.e., electromagnetic waves at a wavelength of about 650 n
Oliff & Berridg,e PLC
Parker Kenneth
Seiko Epson Corporation
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