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Locally Erasable Opto Thermally Addressed Liquid Crystal Display

IP.com Disclosure Number: IPCOM000080092D
Original Publication Date: 1973-Oct-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Laff, RA: AUTHOR [+2]

Abstract

Sasaki has shown that hysteresis is present in the scattering-coefficient vs temperature curve of some liquid crystal materials. When an aligned liquid-crystal is heated above a phase transition temperature Tp, disorder is produced. When the liquid crystal is then cooled below that temperature, to an ambient temperature Ta, that disorder (which causes scattering of light) is frozen in. Maydan/2/ has demonstrated that a display can be made in which the writing is supplied by heat from a laser beam. He demonstrates that erasure can be obtained by supplying an audiofrequency electric field Eh across the liquid crystal cell while it is at ambient, causing it to realign. This erasure occurs throughout the liquid crystal cell.

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Locally Erasable Opto Thermally Addressed Liquid Crystal Display

Sasaki has shown that hysteresis is present in the scattering-coefficient vs temperature curve of some liquid crystal materials. When an aligned liquid- crystal is heated above a phase transition temperature Tp, disorder is produced. When the liquid crystal is then cooled below that temperature, to an ambient temperature Ta, that disorder (which causes scattering of light) is frozen in. Maydan/2/ has demonstrated that a display can be made in which the writing is supplied by heat from a laser beam. He demonstrates that erasure can be obtained by supplying an audiofrequency electric field Eh across the liquid crystal cell while it is at ambient, causing it to realign. This erasure occurs throughout the liquid crystal cell.

A method is proposed whereby local erasure can be accomplished by a heat pulse of the same type used to write the information onto the liquid-crystal cell, during a time in which an electric field E1<Eh is applied. The basis of the effect is: The field E1 is of insufficient magnitude to cause erasure while the material is at ambient temperature, within any reasonable time. However, the viscosity of these materials is known to drop sharply with increasing temperature. Therefore, the mechanism of realignment in the electric field can take place very rapidly at an elevated temperature, as the material cools through the transition temperature Tp. This method thereby allows writing and erasure to be symmetrical operations with a laser-beam addressed to local regions of a liquid crystal panel. The electric field E1 is impressed across the entire area of the panel, as described by Maydan. This scheme allows the option of making a positive or negative display, with re...