Bistable nematic liquid crystal device with bigrating alignment

Details Bistable nematic liquid crystal device with bigrating alignment Bistable nematic liquid crystal device with bigrating alignment

1996-09-20

1998-08-18

Gross, Anita Pellman

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

349177, 349180, 349128, G02F 11337, G02F 113

Patent

active

057964599

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to bistable nematic liquid crystal devices.
2. Discussion of Prior Art
Liquid crystal devices typically comprise a thin layer of a liquid crystal material contained between cell walls. Optically transparent electrode structures on the walls allow an electric field to be applied across the layer causing a re-ordering of the liquid crystal molecules.
There are three known types of liquid crystal material, nematic, cholesteric, and smectic each having a different molecular ordering. The present invention concerns devices using nematic materials.
In order to provide displays with a large number of addressable elements it is common to make the electrodes as a series of row electrode on one wall and a series of column electrodes on the other cell wall. These form eg an x,y matrix of addressable elements or pixels and, for twisted nematic types of devices, are commonly addressed using rms addressing methods.
Twisted nematic and phase change type of liquid crystal devices are switched to an ON state by application of a suitable voltage, and allowed to switch to an OFF state when the applied voltage falls below a lower voltage level, ie these devices are monostable. For a twisted nematic type of device (90.degree. or 270.degree. degree twist as in U.S. Pat. No. 4,596,466), the number of elements that can be rms addressed is limited by the steepness of a device transmission vs voltage curve as details by Alt and Pleschko in IEEE Trans ED vol ED 21 1974 pages 146-155. One way of improving the number of pixels is to incorporate thin film transistors adjacent each pixel; such displays are termed active matrix displays. An advantage of nematic type of devices is the relatively low voltage requirements. They are also mechanically stable and have wide temperature operating ranges. This allows construction of small and portable battery powered displays.
Another way of addressing large displays is to use a bistable liquid crystal device. Ferroelectric liquid crystal displays can be made into bistable device with the use of smectic liquid crystal materials and suitable cell wall surface alignment treatment. Such a device is a surface stabilised ferroelectric liquid crystal device (SSFELCDs) as described by: --L J Yu, H Lee, C S Bak and M M Labes, Pys Rev Lett 36, 7, 388 (1976); R B Meyer, Mol Cryst Liq Cryst, 40, 33 (1977); N A Clark and S T Lagerwall, Appl Phys Lett, 36, 11, 899 (1980). One disadvantage of ferroelectric devices is the relatively large voltage needed to switch the material. This high voltage makes small portable, battery powered displays expensive. Also these displays suffer from other problems such as lack of shock resistance, limited temperature range and also electrically induced defects such as needles.
If bistable surface anchoring can be achieved using nematics then a display can be made which has the merits of both the above mentioned technologies but none of the problems.
It has already been shown by Durand et al that a nematic can be switched between two alignment states via the use of chiral ions or flexoelectric coupling; A Gharbi, R Barberi, G Durand and P Martinot-Largarde, Patent Application No WO 91/11747, (1991) "Bistable electrochirally controlled liquid crystal optical device". G. Durand, R Barberi, M Giocondo, P Martinot-Largarde, Patent Application No WO 92/00546 (1991) "Nematic liquid crystal display with surface bistability controlled by a flexoelectric effect". These are summarised as follows:
In Patent Application No WO 91/11747 a device is described with the following characteristics:
1. The cell is made using two surfaces which have SiO coatings of appropriate thickness and evaporation angle to allow two stable states to exist on each surface. Furthermore the two states on a surface are designed to differ in azimuthal angle by 45.degree. and the surfaces are oriented such that each of the two resulting domains are untwisted.
2. The cell (of 6 .mu.m thickness) is filled with 5 CB doped with 0.5% benzyl quin

REFERENCES:
patent: 4239345 (1980-12-01), Berreman et al.
patent: 4333708 (1982-06-01), Boyd et al.
patent: 4601544 (1986-07-01), Cheng et al.
patent: 4834500 (1989-05-01), Hilsum et al.
patent: 5357358 (1994-10-01), Durand et al.
patent: 5384650 (1995-01-01), TeKolste et al.

Affiliated with

Also associated with

Rating

Bistable nematic liquid crystal device with bigrating alignment does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Bistable nematic liquid crystal device with bigrating alignment , we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Bistable nematic liquid crystal device with bigrating alignment will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1119534