Supertwisted bistable twisted nematic

The degree of stability of supertwisted bistable twisted nematic (SBTN) displays is shown to improve considerably in nematic twist configurations generated by photoaligned and domain-stabilized bias tilt angle patterns on one or both display substrates. Incorporation of uniaxial optical retarders into SBTN-LCD was shown to result in black and white display operation. 

Figure 6.1 Optically bistable, photoaligned, supertwisted nematic LCD [1]. Reproduced from M. Stalder and M. Schadt, Photoaligned bistable twisted nematic liquid crystal displays. Liquid Crystals 30, 285 (2003)...

The effects of bistability and hysteresis in supertwisted nematic layers were first investigated in [122]. To obtain twist angles larger than 90 , nematics were doped with a small amount of an optically active material. Thus a cholesteric (or chiral nematic) with a large pitch P was created, so that the pitch value had to adjust the boundary conditions for the directors on the substrates. The corresponding texture was first discovered by Grandjean and is discussed in Chapter 6. In 1984 the display based on the Supertwist Birefringent Effect (SBE) was proposed [123]. 

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