A Thin Film Process to Improve off Axis Viewing of Liquid Crystal Displays

A well known technique to obtain homogeneous alignment of nematic liquid crystals with positive dielectric anisotropy for use in twisted nematic displays is to deposit a silicon monoxide film onto the aligning substrate surface at an oblique angle between 3–6°. This range of deposition angles provides excellent normal contrast ratio but is poor when viewed off axis. This paper describes an alternative approach utilizing a double SiO deposition that improves off axis viewing. The first SiO layer (350 Å) was deposited at 6°. The second layer (20–50 Å) was deposited at 30°. The second layer seems to have a smoothing effect on the 6° structure, as substantiated by TEM studies, thus lowering the tilt angle.