Examination Committee

Prof Brian K W MAK, CSE/HKUST (Chairperson)
Prof Hoi Sing KWOK, ECE/HKUST (Thesis Supervisor)
Prof Martin SCHADT, Nanjing University (External Examiner)
Prof Zhiyong FAN, ECE/HKUST
Prof V G CHIGRINOV, ECE/HKUST
Prof Ping SHENG, PHYS/HKUST

Abstract

Thought brushed polyimide is commercially widely used in LCD production there are many problems associated with mechanical rubbing; dust acting as nucleation seeds is one. By controlling nucleation, it becomes an advantage for bistable nematic liquid crystal displays. Fast responding, bistable twisted nematic displays (TN-LCDs) with high contrast and low driving voltage based on PI-alignment layers enabling controlled nucleation are reported. Controlled nucleation is powerful because of its simple structure and its compatibility with current LCD fabrication technologies.

Photoalignment has been acknowledged as replacement for the conventional method of rubbed PI. It avoids mechanical rubbing defect lines and static charging problems created by rubbing. The Azo-dye material azobenzene sulfuric dye SD1 developed at CDR is one of the promising photo-alignment materials. However, the re-writing behavior of SD1 which is inherent to Azo needs to be stabilized for most LCD applications. In this proposal, two we propose two methods for stabilizing SD1 alignment.

The first is a stacking alignment method. The alignment film configuration consists of a stack of a thin photo-polymerisable liquid crystal pre-polymer film on top of an azo dye photo-alignment layer. The liquid crystal polymer layer prevents the alignment direction of the azo dye to be rewritten after the liquid crystal polymer is polymerized. The resulting liquid crystal polymer (LCP) alignment surface is robust and exhibits excellent stability.

The key feature nother new stabilization is a mixing a liquid crystal pre-polymer with SD1. Films made with the novel alignment material exhibit as good alignment as those of pure azo-dye materials. Since no additional top layer is needed in this case and no additional synthesis effort is required, this method presents an easy way for fabricating stable LC-alignment films. Photo-stability against exposure to white and blue light is much improved compared with a pure SD1 layer.