Clear vision needs no staying power

An LCD display technology has been developed that produces images which will remain stable, even if left unpowered for several months. Monochrome is already developed, and colour is expected to come to market within nine months. Laptops and PDAs so equipped should be able to run for hundreds of hours on a single battery charge, greatly increasing productivity for those on the move and improving battery life – a constant problem for those with portable appliances. Long term readers of this magazine may be forgiven for a slight feeling of deja-vu, since it was back in August 1985 that STC Laboratories received Eureka’s Finniston Award for its non-volatile LCD screen based on Smectic A, as opposed to twisted Nematic liquid crystals. This new screen technology, from ZBD Displays, is spun out of the original home of liquid crystal displays, DERA (now QinetiQ) at Malvern. Unlike other bi-stable liquid crystal technologies, it uses the same liquid type molecules used in conventional LCDs. The difference is that one of the rubbed alignment layers is replaced by a grating, so the crystals sit in one of two or more stable orientations in the zenithal plane – the plane normal to the grating cells. Switching from one direction to the other occurs after a voltage pulse of appropriate polarity. The basic device is monochrome but, by subdividing the cells into regions of different shape, it is possible to have the molecules switch and latch at different voltages. In this way, it is possible to produce grey scales and, with the addition of filters, colour. The other big breakthrough was a partnership, not with a traditional British company, but with Varitronix, an aggressive Hong Kong-based display company with an annual turnover of $200 to $300 million per year. The result is that the venture is expected to produce full grey scale and colour demonstrators in three to six months, and commercial colour screen samples in nine. Cost and yield are expected to be about the same as those of traditional LCD displays. The viewing angle is almost 180° without any need for compensating film, the contrast ratio is 25:1 and, in reflective mode, reflectivity is 39% – close to the maximum possible with two polarisers. Monochrome text and graphic display samples shown to Eureka could easily be read in the gloom of a London restaurant bar, even though they had been left unpowered for some weeks. Customer interest not only include manufacturers of mobile phones and PDAs, but also those involved with supermarket shelf displays and signage. TS