Picture perfect


By Barry Fox MAKING giant flat television screens may one day be possible now that a way has been found to seamlessly stitch liquid crystal displays together. Electronics giant Philips is so impressed with the idea that it has bought a stake in the company that dreamt it up, Rainbow Displays of Endicott in New York state. Simply making LCD panels larger is impractical because LCDs are made by depositing all the components on a glass plate in a precise pattern. The risk of defects, which appear as an all-too obvious permanently-lit pixel, increases as the area of the panel increases. And until now, tiling together several LCD panels to make bigger displays, as several Japanese companies are attempting to do, has not worked because the joints always showed. One of Rainbow Displays’s vice-presidents, Stephen Sedaker, thinks they are chasing a red herring by trying to make the seams between panels mechanically perfect. “We think that just isn’t possible. Instead, we create the illusion of a perfect seam,” he says. The company has proved that it can do it by invisibly stitching together four panels, each with an 18-centimetre diagonal, to create a 36-centimetre screen with a resolution of 800 by 600 pixels. While the prototype is relatively small, the technology could be used to create much bigger screens. In the near term, RDI says they will soon knit together four 50 centimetre panels—to give a one metre screen that is much lighter, thinner and draws far less power than today’s bulky plasma screens or cathode ray tubes. “I saw the first working prototype in January,” says Hafiz Haq, a vice-president at Philips’s flat panel display group in San Jose, California. “The seams were visible and I told them so. Within two months, the seams had gone.” Although Rainbow Displays says that details of the technology are top secret, New Scientist has found the details in patents published in the US. In these, the company and inventors Che-Yu Li, Peter Krusius and Donald Seraphim point out that the seams between panels will be visible if the LCD cells are further apart at the join than they are over the rest of the panel. So Rainbow Displays is making LCD panels with slightly wider than usual cell spacing. This slightly reduces the picture definition for viewers close to the screen, but most large screens will be viewed from a distance, so this loss of resolution doesn’t matter. But LCD seams also show if light gets round the colour cells as well as through them. To prevent this, the entire screen is covered with a perforated mask that lets light pass only through the cells. But this makes the screen look dim unless viewed from directly in front, so the mask is overlaid with a mosaic of lenticular microlenses to widen the viewing angle. The glass on which the LCD panels are laid down is normally hewn from large sheets of glass using a diamond saw wheel. But this creates a messy edge. To make a cleaner, sharper edge for joining to other panels, Rainbow Displays cuts the glass by scribing and fracturing it,
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