Novel liquid crystal mixtures for a surface-stabilized ferroelectric LCD

We synthesized novel fluorine-substituted chiral compounds having a fluorine atom at an asymmetric carbon and a difluorinated biphenyl ring as a core of a liquid crystal molecule by means of an original method. The ferroelectric mixtures were obtained by mixing the chiral compounds with the non-chiral liquid crystal mixture with a wide SmC temperature range between -29 degrees C (crystallized) and 78 degrees C. They show a large P-s greater than 10 nC cm(-2) at 5 wt % of the chiral compound. Two types of cell, called 'parallel' and 'antiparallel', were fabricated according to the relative direction of the rubbing direction on the substrates. The parallel cells filled with the FLC mixtures show the usual bistable SSFLC (surface-stabilized ferroelectric liquid crystal). The fast response time of 60 mu s (22V(pp) pulse width 250 mu s, at room temperature) was obtained. The apparent cone angle was 45.2 degrees in the switching state and 40.5 degrees in the memory state. On the other hand, the antiparallel cells show an unusual monostable behaviour, i.e. the director falls back to the original configuration when the applied voltage is switched off. The surface-stabilized monostable cells show very attractive characteristics for application for a TFT-active matrix LCD; a high contrast of 81:1, a fast response time (of the order of 1 ms), and an analogue-grey scale with excellent linearity within the low voltage range below 4V.