26.3: Low Voltage Zenithal Bistable Devices with Wide Operating Windows

Abstract

Key parameters for any bistable device are operating voltage and temperature range. The development of liquid crystal mixtures for use with grating aligned Zenithal Bistable Displays (ZBD™) is described for the first time. Latching at voltages less than 5V, with 20V addressing faster than 80μs per line and operation over a temperature range from −20°C to 80°C are all demonstrated in the same 4μm device.

Zenithal bistable device: Comparison of modeling and experiment

“…A thermal glue seal is used to hold the plates together and nematic liquid crystal introduced under vacuum through capillary forces. Throughout this work, Mixture B from [11] was used, together with Nissan SE3510 as the polyimide on the opposing monostable surface. The Gooch Tarry first minimum for this liquid crystal is for a 5 micron cell gap, though devices of different spacing are used for the experimental work.…”

“…It has been theoretically confirmed [7,8,9,10] that the flexoelectric properties of the liquid crystal allow it to respond to the sign of an applied electrical signal, thus providing a means to electrically select either bistable state. In practice, bipolar electrical pulses are used to reduce the effects of ions within the liquid crystal during switching [11] and also serve to keep defect nucleation and annihilation as surface phenomena. The trailing edge of the bipolar pulse selects the latched state.…”

Competing alignments of nematic liquid crystals on square-patterned substrates

“…Pattern-stabilized bistability has now been established for the blazed grating structure of zenithally bistable devices [2,3], the two-dimensional array of post-aligned bistable nematic [4] devices, and, more recently, a steric square-well arrangement [5,6]. In each of these, the bistability pertains between one state with a continuous director arrangement and a second containing orientational defects that are pinned in some way by the substrate inhomogeneity.…”

Nematic liquid crystal alignment on chemical patterns

“…The ZBD (Zenithal Bistable Device) [16,17] achieves this by using a blazed grating which has stable "continuous" and "defect" states. In recent years, much attention has been given to bistable switching in LC devices due to its potential to achieve high display resolution with significantly decreased power consumption.…”