Study on Reverse Twist Depending on Rubbing Direction for Fringe-Field Switching Mode

Abstract

We studied the reverse twist near the pixel edge depending on the rubbing direction for the fringe-field switching (FFS) mode. At the active region, liquid crystal (LC) dynamics and transmittance are the same, irrespective of the rubbing direction, that is, clockwise or counterclockwise with respect to the x-axis, because only one electric field direction exists. On the other hand, LC dynamics and transmittance near the pixel edge, where various field directions are generated, depend on the initial rubbing direction because the position of the reverse twist is decided by the angle between the electric field direction and LC director under a bias voltage. For example, when the rubbing angle is 7°, the reverse twist appears at the bottom of the right sharp corner of the pixel edge so that the reverse region exists far from main active region. However, when the rubbing angle is -7°, the reverse twist appears on top of the right sharp corner of the pixel edge, resulting in the region becoming closer to the main active area and the unstable disclination lines (DLs) easily intruding into the active region. Therefore, it is necessary to keep the reverse twist region far from the active region and this is possible by controlling the rubbing direction in the design of a pixel electrode. As a result, we can minimize the permeation of DLs into the main active region.