GB1387317A - Electro-optical display cell - Google Patents

Abstract

1387317 Modulating light LICENTIA PATENT-VERWALTUNGS-GmbH 19 April 1972 [21 April 1971] 18167/72 Heading H4F In a electro-optic cell, material in the nematic phase and having negative dielectric anisotropy is disposed between two electrods so as to form a uniaxial layer (homeotropic alignment) with the unique exis substantially normal to the electrode surfaces. On application of a D.C. or A.C. potential difference above a threshold level between the electrode, the nematic layer, while remaining uniaxial, has its axis tilted with respect to the original axis (tilting of the molecular long axes from the 90 degree alignment relative to the electrodes), so that whereas the layer formerly appeared isotopic to plane polarized light at normal incidence, it becomes birefringent. Further increase of the applied potential difference leads to dynamic scattering, but this may be counteracted by increasing the frequency of the potential difference. To modulate white or monochromatic light, the cell may be disposed between crossed, parallel or intermediate positioned polarizers, using the variation in birefringence. Alternatively a pleochroic dye may be added to the nematic layer for variable light absorption thereby if the emergent light is passed through an analyser, the colour thereof is further modulated. As particularly described, the electrodes are both transparent, or one transparent and one reflective. The transparent electrodes are tin dioxide coated glass, prepared by heating to close to the melting point of the glass and subsequent cooling. The electrodes may be subdivided, e.g. X and Y address lines on opposite plates, for selective addressing. Since the threshold potential difference V schw , e.g. 10 V., is more than half the potential difference V s at which the maximum effect is obtained (V s -V schw is approximately IV) lines may be enrgized at V s /2 without cross-talk. The water content of the nematic layer is preferably less than 0.1%.