Browse Prior Art Database

HIGH SPEED FERROELECTRIC LIQUID CRYSTAL DEVICES WITH CONTROLLED BISTABILITY

IP.com Disclosure Number: IPCOM000025764D
Original Publication Date: 1987-Dec-31
Included in the Prior Art Database: 2004-Apr-04
Document File: 2 page(s) / 101K

Publishing Venue

Xerox Disclosure Journal

Abstract

Surface stabilized ferroelectric liquid crystals (FLC's) may be used in displays, image bars, and shutters, because their high polarizations, coupled to applied fields, generate large torques which enable fast devices. The surface stabilized structure establishes two surface states which enable bistability to occur. With bistability, a state is maintained even after the driving voltage is reduced to zero.

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XEROX DISCLOSURE JOURNAL

HIGH SPEED FERROELECTRIC Proposed Classification LIQUID CRYSTAL DEVICES WITH
CONTROLLED B I STAB I LITY
Joseph J. Wysocki

U.S. C1.350/331R Int. C1. G02f 1/133

Surface stabilized ferroelectric liquid crystals (FLC's) may be used in displays, image bars, and shutters, because their high polarizations, coupled to applied fields, generate large torques which enable fast devices. The surface stabilized structure establishes two surface states which enable bistability to occur. With bistability, a state is maintained even after the driving voltage is reduced to zero.

There are some devices where the degree of bistability needs to be controlled. Displays with gray scale and high speed optical shutters are two examples where the zero voltage state needs to be controlled. In a gray scale scheme involving pulse width modulation, bistability reduces the effect of width modulation since the device stays in its last driven state, instead of returning to the original, pre-driven state when the voltage is removed. In a high speed shutter, again, the driven state should persist for a time period as long as the drive pulse, or shorter, but not longer. There are several ways to control bistability and obtain more effective devices where such control is necessary. One way, and probably not a preferred way, is to abandon use of the surface stabilized structure completely and to depend u on scattering of light for the optical effect as the helical structure of the FL

              8 unwinds and rewinds. This way unfortunately does not provide fast response time. Three possible ways of controlling bistability with the surface stabilized structure are as follows. The first is the use of ions added to the FLC which are "plated out" on the alignment surfaces during a drive pulse and...