GB1506331A - Liquid crystal display devices - Google Patents

Abstract

1506331 Matrix displays SIEMENS AG 14 Sept 1976 [22 Sept 1975 (2)] 37957/76 Heading G5C [Also in Division G2] In a display device in which cholesteric liquid crystal material with positive anisotropy is converted to a nematic phase by a magnetic or electric field above a threshold E cn , may be converted back to the cholesteric phase below a threshold E nc , and may have either phase at an intermediate field Eh, where E nc #E h <E cn , means are provided which can selectively apply any of the three field values to an addressed region of the liquid crystal material such that when the field E h is applied, material surrounding the region receives a field greater than E cn . This maintains a border of nematic phase material which prevents more outlying cholesteric regions expanding into the addressed region when it is in its nematic state (the latter being only quasi-stable at E h ). The preferred embodiments are electrically addressed X-Y transmissive matrices, but alphanumeric segmented electrodes are also referred to. One or both sets of column and row electrodes are provided either with overlying electrode members (e.g. in the form of a ladder or longitudinal ribs at either side of each electrode strip), or an overlying dielectric island centred on each addressed region, or overlying continuous dielectric strip central of each electrode strip. Fig. 7 shows dielectric strips 11 and electrodes 3, arranged with tapering side edges, formed by etching two continuous superimposed layers for a limited period. The angle between the tapering edges is preferably greater than 20 degrees. The associated field distribution is shown at 16.