Ferroelectric liquid crystal devices

Details Ferroelectric liquid crystal devices Ferroelectric liquid crystal devices

1996-06-18

1998-10-13

Kelly, C. H.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

25229961, 25229962, 25229963, 25229965, C09K 1912, C09K 1934, C09K 1932, G02F 113

Patent

active

058207864

DESCRIPTION:

BRIEF SUMMARY
FERROELECTRIC LIQUID CRYSTAL DEVICES

This application is a 35 USC371 of PCT/GB94/02693 filed Dec. 9, 1994, published as WO95/16760 Jun. 22, 1995.
This invention relates to ferroelectric liquid crystal devices and ferroelectric liquid crystal mixtures. Liquid crystal devices commonly comprise a thin layer of a liquid crystal material contained between two glass slides. Optically transparent electrodes are formed on the inner surface of both slides. When an electric voltage is applied to these electrodes the resulting electric field changes the molecular alignment of the liquid crystal molecules. The changes in molecular alignment are readily observable and form the basis for many types of liquid crystal device.
In ferroelectric liquid crystal devices the molecules switch between different alignment directions depending on the polarity of an applied electric field. These devices often exhibit bistability where the molecules tend to remain in one of two states until switched to the other switched state. This allows the multiplex addressing of quite large and complex devices.
One common multiplex display has display elements. ie pixels, arranged in an x, y matrix format for the display of eg, alpha numeric characters. The matrix format is provided by forming the electrodes on one slide as a series of column electrodes, and the electrodes on the other slide as a series of row electrodes. The intersections between each column and row form addressable elements or pixels. Other matrix layouts are known, eg seven bar numeric displays.
There are many different multiplex addressing schemes. A common feature involves the application of a voltage, called a strobe voltage to each row or line in sequence. Coincidentally with the strobe applied at each row, appropriate voltages, called data voltages, are applied to all column electrodes. The differences between the different schemes lies in the shape of the strobe and data voltage waveforms.
Other addressing schemes are described in GB-2,146,473-A; GB-2,173,336-A; GB-2,173,337-A: GB-2,173,629-A; Wo 89/05025; Harada et al 1985 S.I.D. Paper 8.4 pp 131-134; Lagerwall et al 1985 I.D.R.C pp 213-221 and P Maltese et al in Proc 1988 IDRC p 90-101 Fast Addressing for Ferro Electric LC Display Panels.
The material may be switched between its two states by two strobe pulses of opposite sign, in conjunction with a data waveform. Alternatively, a blanking pulse may be used to switch the material into one of its states. Periodically the sign of the blanking and the strobe pulses may be alternated to maintain a net d.c. value.
These blanking pulses are normally greater in amplitude and length of application than the strobe pulses so that the material switches irrespective of which of the two data waveforms is applied to any one intersection. Blanking pulses may be applied on a line by line basis ahead of the strobe, or the whole display may be blanked at one time, or a group of lines may be simultaneously blanked.
It is well known in the field of ferroelectric liquid crystal device technology that in order to achieve the highest performance from devices, it is important to use mixtures of compounds which give materials possessing the most suitable ferroelectric smectic characteristics for particular types of device.
Devices can be assessed for speed by consideration of the response time vs pulse voltage curve. This relationship may show a minimum in the switching time (t.sub.min) at a particular applied voltage (V.sub.min). At voltages higher or lower than V.sub.min the switching time is longer than t.sub.min. It is well understood that devices having such a minimum in their response time vs voltage curve can be multiplex driven at high duty ratio with higher contrast than other ferroelectric liquid crystal devices. It is preferred that the said minimum in the response time vs voltage curve should occur at low applied voltage and at short pulse length respectively to allow the device to be driven using a low voltage source and fast frame address refresh rate.
Typical known materials (

REFERENCES:
patent: 5147577 (1992-09-01), Gray et al.
patent: 5384071 (1995-01-01), Gray et al.
patent: 5456859 (1995-10-01), Gray et al.
patent: 5486309 (1996-01-01), Gray et al.
patent: 5501818 (1996-03-01), Shinjo et al.
patent: 5512208 (1996-04-01), Terada et al.
patent: 5514297 (1996-05-01), Shinjo et al.
patent: 5599479 (1997-02-01), Shinjo et al.
patent: 5611957 (1997-03-01), McDonnell et al.

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