Fast bistable nematic display from coupled surface anchoring breaking

We present new experimental results on bistable nematic display, controlled from surface anchoring breaking. Using simple planar anchorings on both plates and chiralized 5CB material, we prepare thin cells with two equal energy states: one uniform planar and the other one twisted by 180 degrees. Applying short electric pulses we break transiently both surface anchorings (to write) or only one of them (to erase). After these short pulses, in absence of any field, we obtain at will the uniform state or the twisted one, with infinite lifetime and full bistability. Using polarizers an optical contrast of 50 is measured between the two states. The write/erase pulse duration is short, comparable with the surface anchoring response time similar to 10 mu s. The optical response time, classically related to the cell thickness, is here in the ms range. The temperature dependence of the threshold is also discussed. The existence of the two relatively close writing and erasing thresholds allows in principle simple multiplexability.