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Abstract

The invention concerns a surface stabilized ferroelectric liquid crystal (SSFLC) display devices. Displays are formed by cells containing a thin layer, e.g. 2 .mu.m thick, of smectic liquid crystal material. The cell walls are surface treated and carry e.g. row and column electrodes forming an x,y matrix of addressable display elements or pixels. These devices can show bistability and switch between their two stable state on application of a dc pulse of appropriate polarity, amplitude and width. In this invention the device is addressed by first preconditioning the liquid crystal material at each pixel by applying one of two different levels of ac bias, thereby changing the switching characteristics of the material, and second by a switching with application of a switching pulse. This results in pixels that have received the first of the ac bias levels switching whilst the other pixels do not switch. The two levels of ac bias may be applied e.g. by a combination of bipolar strobe pulses and two bipolar data waveforms applied in a multiplex addressing manner to the row and column electrodes. The subsequent switching pulse may be shared between row and column electrodes to give a resultant pulse of appropriate polarity, amplitude and width.

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First Claim