Abstract

Liquid crystals are customarily used in several kinds of flat panel displays. Besides usual nematic liquid crystals, smectic tristate antiferroelectric liquid crystals have shown analogue grayscale and full color video rate at high-end devices with passive multiplexing. These devices ultimately are intended to be applied to small size devices on microdisplay applications. When a symmetric driving signal is applied, the electrooptic response of the devices usually consists of two symmetric hysteresis lobes. An asymmetric hysteresis cycle can be developed by using dissimilar aligning layers onto the two glass plates of the cell. This kind of devices can lead to analogue optical multistability, i.e., devices whose optical transmission may be arbitrarily set and maintained reducing or eliminating the bias voltage. In this work, a study of the asymmetric behavior of cells filled with commercial antiferroelectric liquid crystal is presented. Optical hysteresis cycles have been obtained applying a low frequency triangular waveform to the devices. Analogue grayscales have been generated only at one lobe of the hysteresis cycle. Electrical characterization has been carried out measuring the switching current of the cells test. Multiplexed driving waveforms have been applied with and without bias voltage in order to evaluate the stability of the optical transmission for video rate working. Results demonstrating analogue optical multistability on asymmetric antiferroelectric cells have been obtained. Narrow dynamic ranges, compatible with standard electronics for dynamic grayscale in data columns have been found. Preliminary measurements of the frequency dependence of impedance have been obtained on the capacitive device.