Surface modification of polyimide alignment films by ion beams for liquid crystal displays

The optically-compensated-bend mode exhibits fast response by switching between two bend states for liquid crystal displays (LCD). However, the initial liquid crystal configuration is in a splay state. It is required to apply a voltage higher than the critical voltage to transit the cells from the splay state to the bend state. The transfer process takes a period of time to stabilize the bend state before the efficient operation could be started, and thus it is termed the warm-up time or transition time. In this study, the surface of polyimide alignment films was modified by ion beams to promote the transition. A large number of nucleation sites were demonstrated to reduce the transition time from 24s to 17s after the effective surface modification by Ar⁺ ion beam. Both H₂ gas and Ar gas were employed as the ion sources at the different 165-250eV energy levels. The surface characteristic analysis results also showed that the room temperature contact angle with water was reduced from 90.1° to 81.7°. In the meanwhile, there was no obvious morphological destruction on the polyimide film surface, which was evidenced by the atomic force microscopy study. In addition, the LCD cells remained an excellent response time of 3.4ms at 5.5V.