Relaxation of Surface Stabilised Antiferroelectric Liquid Crystals at Video Frequency

Abstract

As part of our line of research into high resolution, video rate antiferroelectric displays we have studied the ferroelectric – antiferroelectric relaxation that follows the data pulse, in surface stabilised antiferroelectric liquid crystal (AFLC) displays, driven by biasless or low bias video frequency waveforms. This generally incomplete relaxation reduces the intensity of the light transmitted by a pixel in any partially ferroelectric (grey-level) state during a video frame, and hence limits the frame-averaged brightness of the AFLC display. The relaxation is a function of the surface stabilisation (i.e., the anchoring strength, pre-tilt and thickness of the device and the pitch of the AFLC), the rotational viscosity of the AFLC, the degree of relaxation of the AFLC between successive frames, the magnitude of the data pulse (grey level) and bias voltage. We have optimised the driving scheme for a number of symmetric and asymmetric (biasless) displays with different antiferroelectric materials and a variety of alignment surfaces, and present mathematical fits to the decaying transparency during single frames as functions of the data pulse. Finally we discuss the mechanisms governing the relaxation.