Highly asymmetric antiferroelectric liquid crystal displays

Antiferroelectric liquid crystals (AFLCs) have been, for a while, promising candidates for display applications. However, their success has been hindered by a poor dark state, and hence a reduced contrast. Various solutions to this problem have been proposed, hereunder the use of so-called orthoconic materials with cone angles close to 45deg and asymmetric cells, where the alignment materials on the two ITO-electrodes are not the same. Whereas the orthoconic materials in theory provide the most elegant solution, the available materials commute too slowly for most live image applications. The asymmetric cells on the other hand, maintain the fast switching inherent to most AFLC devices, and they show a much improved off state. However, they have up to now showed the very undesirable feature of memory effect, i.e. the transmission of a pixel in one frame depends on the transmission of the previous. In this work we use asymmetric cells, where one of the ITO-electrodes is covered with low energy surface material (a fluorinated block copolymer (FBC)), which are characterised by an unusually large voltage shift in the electro-optical response. We exploit the large voltage shift to employ an efficient erasing strategy, to reduce the memory of the device, and we eliminate any flickering of the device by only addressing the grey levels in one of the hysteresis loops.