This paper presents the development of an electrical SPICE model of a Ferroelectric Liquid Crystal (FLC) on silicon microdisplay. Previous work has investigated the use of an electro-optical SPICE model to simulate the optical response of an FLC cell to a given electrical signal. However, the design of the backplane drive scheme for the display also requires an accurate model of the electrical load represented by an FLC cell. The model presented here provides a good fit to electrical measurement results and, in addition, can be combined with elements of the electro-optical model to allow the optical response of the cell to be modelled at the same time. This paper also presents results of charge collection current measurements which highlight the differences in the behavior of the cell when it is switched between positive and negative voltages and then in the other direction.
Optimal performance of a Liquid Crystal on Silicon (LCoS) device requires an integrated approach incorporating both optical and electrical design elements. In particular, during the design of both the IC back plane and the voltage waveforms used to drive fast switching Ferroelectric LC (FLC) the electro-optical properties of the LC must be considered to ensure that the best use is made of the FLC. Although, SPICE equivalent circuits for FLC materials have been developed and can be used for this purpose their accuracy relies upon the measurement of a number of parameters. Unfortunately, the accuracy of measuring key parameters is often poor, resulting in a relatively large margin of error in the final model. However, this need not be the case. In this paper we present a methodology which uses standard IC parameter extraction software to simulate and optimize the FLC SPICE model parameters such that the model closely matches the measured response of the sample. By using this approach we identify a set of parameters which when combined provide a SPICE equivalent circuit which models the FLC repsonse to a given input waveform.
Defect free homogeneous alignment of ferroelectric liquid crystals in the surface stabilized configuration remains challenging to obtain even over the relatively small area of liquid crystal on silicon microdisplays. The limitations of the conventional rubbed polymer alignment technique are discussed and the benefits brought by recent advances in backplane post-processing are demonstrated in realistic conditions. The potential of the linearly photopolymerized photoalignment technique are highlighted in terms of alignment quality, susceptibility to zigzag defects, and electro-optical performances.
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