Driving voltage of reflective cholesteric liquid crystal displays

The reflective cholesteric texture mode between planar and homeotropic textures, which can achieve a high contrast ratio, needs to be coupled with an active matrix drive scheme such as a method using thin film transistors. In this article, the threshold voltage of the cholesteric-nematic phase transition, an important characteristic related to the requirements of active matrix drive schemes, is discussed. We investigated the role of the cell gap in determining the reflectance, and studied the effects of varying the nematic liquid crystal and chiral component of the cholesteric mixture. The cell gap needs to be optimized for lower threshold voltage and higher reflectance. The chiral component and the nematic liquid crystal both have a strong effect on the threshold voltage. On the basis of these results, novel chiral materials are proposed. This study demonstrates that some of these materials successfully contribute to the reduction of the threshold voltage. (C) 1999 American Institute of Physics. [S0021-8979(99)05311-6].