Homogeneous electric field threshold switching phenomena in a multiplexible bistable liquid crystal display

Abstract

An electrically addressed, thermally erased bistable nematic liquid crystal display with a potentially very large multiplexing capacity is described. A simple, uniform electric field geometry produces a nearly ideal electro-optic threshold response, with a very sharply defined threshold field and rapid saturation. The threshold is analytically shown to depend on the binding energy of disclination lines at a spatially finite surface orientational discontinuity. Moreover, the binding energy changes in time as the orientational discontinuity at the binding site is altered by the movement of a twist wall away from the junction. The nature and dynamics of this domain wall are described, as are the different distorted boundary layer configurations that arise in a uniform field geometry. The movement of this wall effectively reduces the binding energy of the disclinations, allowing switching to occur at lower fields. A dramatic voltage reduction is achieved with a short, low voltage pulse applied to prime the device prior to the onset of the switching pulse. This reduction makes 2:1 addressing possible at high speed (2 msec), using row and column voltage levels of approximately ±50 V. Similarly, 3:1 addressing is achieved with select and nonselect levels of 70 and 35 V, respectively. The high addressing speed results from the requirement of only a minimal amount of disclination movement, with the self-propelled annihilation of the detached loops carrying the switching process to completion thereafter.