Co-ordinate addressing of smectic display cells

Claim 1

A method of co-ordinate matrix addressing in internally electroded liquid crystal display cell which has a layer of smectic material sandwiched between two electroded plates crossing over a second array on the other plate defining therebetween a set of elemental volumes of liquid crystal each element of which is defined by the thickness of the liquid crystal layer and the area of overlap where a member of the first array crosses over a member of the second, wherein the smectic material exhibits positive dielectric anisotropy and has an electrical conductivity large enough for dynamic scattering to be capable of being produced by the application of an electric field across the layer, and wherein at least one of the plates is transparent and its surface in contact with the liquid crystal layer is such that, when the layer is taken into a smectic phase from less-ordered non-smectic phase by cooling in the absence of an applied field, those molecules of the layer adjacent said surface are caused to assume substantially homeotropic alignment, which method includes the steps of applying an electric potential between the members of the first array and those of the second in such a way as to cause dynamic scattering in said set of elemental volumes, converting the dynamic scattering in the set of elemental volumes into static focal-conic scattering by removal of said potential, and selectively restoring individual elemental volumes to non-scattering substantially homeotropically aligned state by the concurrent application of direct voltage signals of predetermined durations and magnitudes to selected electrodes in said arrays such that not more than ten direct voltage resultant switching pulses are applied between the two electrodes defining any elemental volume.

Claim 2

A method of co-ordinate matrix addressing in internally electroded liquid crystal display cell which has a layer of smectic material sandwiched between two electroded plates crossing over a second array on the other plate defining therebetween a set of elemental volumes of liquid crystal each element of which is defined by the thickness of the liquid crystal layer and the area of overlap where a member of the first array crosses over a member of the second, wherein the smectic material exhibits positive dielectric anisotropy and has an electrical conductivity large enough for dynamic scattering to be capable of being produced by the application of an electric field across the layer, and wherein at least one of the plates is transparent and its surface in contact with the liquid crystal layer is such that, when the layer is taken into a smectic phase from less-ordered non-smectic phase by cooling in the absence of an applied field, those molecules of the layer adjacent said surface are caused to assume substantially homeotropic alignment, which method includes the steps of applying an electric potential between the members of the first array and those of the second in such a way as to cause dynamic scattering in said set of elemental volumes, converting the dynamic scattering in the set of elemental volumes into static focal-conic scattering by removal of said potential, and selectively restoring individual elemental volumes to non-scattering substantially homeotropically aligned state by the concurrent application of direct voltage signals of predetermined durations and magnitudes to selected electrodes in said arrays such that not more than ten direct voltage resultant switching pulses are applied between the two electrodes defining any elemental volume.