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ZBD's epaper for retail technology
The Zenithal Bistable Display (ZBD®) is the first commercially available LCD that uses surface bistability. It has the same basic construction as the conventional twisted-nematic (TN) display used in watches. Two glass, or plastic, substrates with ITO electrodes on both internal surfaces, over-coated with a polymer layer to provide alignment to the liquid crystal, are spaced about 5 micron apart. It differs in construction in only one respect: instead of the usual rubbed polymer alignment layer usually used for the TN, one of the surfaces of the ZBD has a patterned or profiled surface designed to induce two or more alignment states. These states have either a low pre-tilt (planar) or a high pre-tilt (homeotropic) and are retained indefinitely after being latched with an appropriate electrical signal. Because the grating offers latching with a well defined threshold, the device can be matrix addressed passively, without cross talk between the rows and columns; no thin-film transistors (TFT) are required to address complex images. Excellent performance characteristics are achieved in a TN-like LCD in which one of the alignment surfaces is a relief grating. Correct design of the grating shape and surface properties not only imparts the bistability, but allows control of the optical performance, the latching voltages, and the temperature range. Being addressed using a simple passive matrix approach, without the need for thin-film transistors, large amounts of information may be displayed using conventional STN drivers. A low cost fabrication method has been devised that is compatible with conventional TN and STN manufacture, and with negligible equipment outlay. These properties make the devices ideal for low power applications where a high information content image is updated infrequently. |
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