Pretilt effect on a vertically aligned liquid crystal cell for optical displays

Abstract

Vertical aligned (VA) mode liquid crystal (LC) cells are very popular in transmissive directview and reflective projection displays because of high contrast ratio and wide viewing angle. A nonzero pretilt angle is generally used to avoid domain formation during molecular reorientation by electric field, as well as to reduce both driving voltage and response time. On the other hand, increasing the pretilt the quality of the dark state will be reduced, and thus an optimal value of pretilt has to be sought. To this aim, even different pretilt values on the two surfaces, yielding an asymmetric tilt distribution, could be considered. The pretilt effect on electro-optical properties of a VA LC cell has been investigated. Pretilt was controlled changing the angle of SiOx deposition on the substrate surfaces [1]. We employed Variable Angle Spectroscopic Ellipsometry [2] to obtain the tilt angle distribution versus the applied voltage. Finally, we compared experimental findings with simulated data at different anchoring energies. The results will be discussed.