Organic polymer o-plate compensator for improved gray scale performance in twisted nematic liquid crystal displays

Abstract

An O-plate compensator comprising an organic liquid crystal polymer, and methods for fabricating the same, are disclosed. The compensator is a uniaxial birefringent thin film with its extraordinary axis oriented obliquely with respect to the surface of the film. (It is noted that the birefringent thin film could be weakly biaxial.) The oblique orientation of the liquid crystal director, which is parallel to the films extraordinary axis, is achieved by casting an organic thin film onto a surface specially prepared for a orienting liquid crystals, such as obliquely deposited SiO, mechanically rubbed alignment agents. The film can either be cast from a solution of the liquid crystal polymer or from a reactive liquid crystal monomer having a nematic phase. Any solvent that may be used during the fabrication process is evaporated off and the organic thin film is held at a temperature in its nematic phase. If a reactive monomer is used, the film is then photopolymerized. Alternative embodiments of an organic O-plate include the use of smectic-A and smectic-C materials. Fabrication techniques employing these materials are described.