US 4,542,960 AGranted

Fringe-field switched storage-effect liquid crystal display devices

AssigneeInternational Business Machines Corporation

InventorKie-Hsiung Yang

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Abstract

A four terminal liquid crystal display device includes orthogonally related row and column electrodes separated by a dielectric and disposed in respective sets above and below the liquid crystal medium. The electrodes in proximity to the LC medium are the column electrodes which have a small alternating square wave bias voltage.+-.Vo imposed therebetween so that a voltage of 2Vo magnitude is normally impressed across the LC medium. When an impulse voltage of magnitude 4Vo is impressed across the exterior row electrodes (+2Vo and -2Vo respectively), since the column electrodes are foraminated or have microapertures therethrough, the electric field established between the row and column electrodes in opposite sets, 3Vo, extends through the microapertures into the LC medium to establish a fringe electric field normal to the surfaces of the column electrodes tending to retain the LC directors in the vertical position. This arrangement avoids the imposition of large voltages directly across the LC media and permits the application of low voltages to the electrodes and thereby increases the life of only the column LC media which are otherwise degraded by high voltages.

Claims18

Dependent claims

A liquid crystal display device including at least one cell having a memory effect comprising:

first and second arrays of column electrodes spaced from each other in parallel planes;
a liquid crystal material contained between said first and second arrays of column electrodes and having respective boundary layers contacting the inner surfaces of said column electrodes;
first and second arrays of row electrodes respectively disposed in parallel planes in proximity to the outer surfaces of, and extending orthogonally to, said first and second arrays of column electrodes;
a first thin dielectric layer disposed between and isolating said first array of column electrodes from said first array of row electrodes;
a second thin dielectric layer disposed between and isolating said second array of column electrodes from said second array of row electrodes;
and
a pair of parallel housing plates for containing said arrays of row and column electrodes and said liquid crystal material therebetween, at least one of said plates being optically transparent;
and wherein each column electrode in said first and second arrays of column electrodes is porous such that potentials applied to said row and column electrodes are capable of producing electrical fringe fields at the porous inner surface of each said column electrode tending to retain the directors of said liquid crystal boundary layers normal to said inner surfaces in the regions of said fringe fields;
whereby said memory effect may be achieved by said fringe fields when appropriate potentials are applied to said arrays of row and column electrodes.

6 more elements

Dependencies are inferred from the claim text.