The recent Bistable Nematic (BiNem<sup>(R)</sup>) LCD technology presents long term bistability, high level passive matrix multiplexing and high optical quality. The BiNem device, based on anchoring breaking, needs specific low anchoring strength materials - alignment layers and liquid crystal mixtures. We present here our approach to develop nematic mixtures with wide enough temperature range and low zenithal anchoring energy.
For mobile devices, permanent image displays are very attractive. We present one: the Binem® display which is close to appear on the market. A first demonstrator was shown at SID’ 97. An important research and development work has been made in the Paris-Sud University and in Nemoptic to increase the temperature domain and define industrial processes to realise mean size displays. The Binem uses two equal lower energy states of a chiral nematic liquid crystal. The molecules are oriented almost parallel to the cell plates by monostable surface treatments. One state (U) is uniform, the other (T), is twisted by 180°.To switch, a high field pulse orients the molecules on one of the plate perpendicular to it: the anchoring is broken. After the pulse, this state is unstable, the molecules on the plate will relax to the anchoring orientation. If they fall in one direction the U state builds, if they fall in the opposite direction the T state is realized. The fall time of the pulse and the pretilts on the two plates control this process. We explain the mechanism of switching by surface anchoring breaking and the obtained display performances.
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 approximately 10 microseconds. 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.