Post Aligned Bistable Nematic Device

The operation of a novel post aligned bistable nematic (PABN) display under development at HP-labs has been successfully modelled using our program. The device consists of LC material sandwiched between two surfaces. The top surface is smooth, while the bottom surface is covered in a regular array of microscopic 3-D posts[1]. It has been possible to simulate the operation of the whole device by considering a single post with periodic boundaries.
Two distinct stable states exist: the tilted and planar states. We have identified that these two states are separated by an energy “barrier” associated with a pair of topological defects located at opposing corners of the posts.

Planar State

Tilted State

In order to switch between the two states, and traverse the barrier, energy must be provided by an external electric field. This is achieved by a pair of electrodes on the top and bottom surfaces of the device. The device can be switched between the two states by applying short pulses of opposing polarities to the electrodes.

The surface of the posts is treated in a way that restricts the director to remain tangential to the LC-solid surface interface at all times. In order to switch between the two stable states where the tilt angles are opposite along the corners, the director field must pass through a high-energy state involving topological defects.

[1]. Kitson S. Geisow A. “Bistable Alignment of Nematic Liquid Crystals Around Microscopic Posts”, Mol. Cryst. Liq. Cryst., vol. 412, pp. 153-161, 2004.

This page last modified 2 June, 2006 by e.willman