Photoalignment of LCoS LCDs

Abstract

Abstract— Because the pixel area of liquid‐crystal‐on‐silicon (LCoS) microdisplays is about 100 times smaller than that of direct‐view liquid‐crystal displays (LCDs), the limitations of the conventional alignment by brushing are obvious: Scratches and particle contamination caused by brushing become visible due to the strong optical magnification required for LCoS LCDs both in front or rear projection. As an alternative, photoalignment with the linear photo‐polymerization (LPP) technology avoids the generation of defects, thus increasing production yields considerably. For application in LCoS LCDs, alignment layer materials must match the high‐voltage holding ratio (VHR) specifications of TFT‐LCDs. The VHR performance of the newly developed second‐generation LPP materials is shown to be similar to standard TFT polyimides used for conventional brushed alignment. We report investigations of pretilt‐angle generation by photoalignment on reflective CMOS substrates. UV light reflected from the CMOS surface during LPP exposure affects the resulting pretilt angle. Compared to pretilt angles on transmissive substrates, the reflected UV light can induce lower, higher, or identical pretilt angles, depending on LPP material properties. In any case, the pretilt angles are well defined, which results in perfect LCD alignment.

Liquid-crystal displays using printed plastic TFT backplanes

“…Instead, we used the StarAlign series alignment materials from ROLIC, Switzerland, where these issues are avoided with a non-mechanical non-contact photo-alignment process. [7][8][9][10][11] A schematic of the processing technique recommended by ROLIC is shown in Fig. 2.…”

P‐76: Economic Wide‐Viewing Angle AMLCD Using Dual‐Domain Photoalignment and a Single Discotic Compensation Foil

“…A 2 inch demonstrator display was made using LPP (Rolic Research Ltd. & Ciba Specialty Chemicals, [5], [6]) photoalignment layer at one substrate and a conventional polyimide rubbing layer at the opposing substrate. The LPP material has C=C double bonds in the side chain which have absorption bands of UV light around 313 nm.…”

A study of electro‐optical characteristics depending on LC pre‐tilt angle and cell gap in a full‐HD LCOS panel

“…For example, the fill factor is decreased and the diffraction loss and fringe-field effect are both increased. 5,6 Maintaining high brightness and high contrast ratios for a high-resolution LCOS is a challenging task.…”