Patent
1987-03-02
1989-01-24
Miller, Stanley D.
350349, G02F 113
Patent
active
047997761
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to reflect type displays and more particularly, to liquid crystal displays which realize to reduce the thickness of the display portion of microcomputers, word processors, televisions, and the like by the provision of a display panel that uses smectic liquid crystal with an added dye, for instance, a ferroelectric liquid crystal (referred to as FLC hereinafter) of the guest-host type, in particular.
2. Description of the Prior Art
Of the solid state display panel, the system which controls each picture element independently is effective for displays with large area. As such a panel there has been known in the past a display in which the multiplexing drive system is applied to a simple matrix structure of the A4 size with 400 elements in the row and 200 elements in the column direction that is formed by the use of a two-frequency liquid crystal, for instance, a twistic nematic liquid crystal (referred to as TN liquid crystal hereinafter). However, to construct a reflection type liquid crystal display by the use such a TN liquid crystal, two-polarizing plates have to be arranged on the outside of a pair of substrates, rotated mutually by 90.degree.. Moreover, a reflecting plate has to be arranged on the outside (namely, on the furthest side with respect to the incident light) of the polarizing plate. Namely, the light path is as follows: The incident light goes through a first polarizing plate, an opposing glass, an opposing transparent conducting film, TN liquid crystals, a transparent conducting film, a glass substrate, a second polarizing plate, and an aluminium reflecting substrate.
Further, light reflected there proceeds backward to the incidence side through the second polarizing plate. However, use of such TN crystals has many drawbacks such as those listed below.
(1) The amount of reflected light is reduced due to the use of two polarizing plates.
(2) There is observed a loss of light due to absorption of light by the glass substrates.
(3) The reflecting plate becomes cloudy due to oxidation of aluminum by the atmosphere, which induces a reduction in the reflectivity.
(4) When active elements are provided on the inside of the substrate, there is generated an absorption loss caused by the organic resin that exists in these surroundings.
The present invention is aimed at solving these problems.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(A) and 1(B) show a plan view and a longitudinal section view of the passive liquid display panel of the present invention.
FIGS. 2(A) and 2(B) show the operation of the ferroelectric liquid crystal used in the present invention.
SUMMARY OF THE INVENTION
In order to solve these problems, in the present invention use was made of ferroelectric liquid crystals that display the chiral smectic C phase (SmC*). Namely, a bistable state can be obtained by setting the separation between the cells to be 4 microns or less.
By mixing liquid crystal material in its isotropic liquid crystal state (high temperature state) in such a thin cell, and by lowering the temperature, SmA and then bistable SmC* are obtained. By so doing, it is possible to loosen the spiral structure. When a voltage is applied to SmC*, molecules are aligned in one direction with an angle of about 45.degree.. By the application of a voltage with opposite sign it is possible to obtain an angle of about -45.degree. (within 45.degree..+-.5.degree.) in the opposite direction. These two states are nonvolatile in the sense that they hardly change even after the voltage is shut off, retaining an angle of about 90.degree. (within .+-.10.degree.). With this observation, it became clear that transmission and nontransmission of light can be accomplished by the use of a single polarizing plate. Because of this, the present invention comprises a pair of substrates (one of the light incidence side is called the opposing substrate and the other one of the other side is called simply the substrate) that form a cell, electrodes (one on the li
REFERENCES:
patent: 4367924 (1983-01-01), Clark et al.
patent: 4634226 (1987-01-01), Isogai et al.
patent: 4707078 (1987-11-01), Geary
Hamatani Toshiji
Inujima Takashi
Konuma Toshimitsu
Koyanagi Kaoru
Mase Akira
Ferguson Jr. Gerald J.
Gallivan Richard
Miller Stanley D.
Semiconductor Energy Laboratory Co,. Ltd.
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