s. Sony and Seiko Epson offer smaller-size displays, too, such as 0.7- or 0.55-inch diagonal for camcorders or virtual-reality goggles, but the current technology delivers image quality that isn't especially sharp at this resolution and size.
However, the new display technologies, just now maturing, could dramatically change the
miniature-display
landscape. These devices significantly advance pixel density, in some cases up to 2500 dpi. Consequently, they are being considered for dozens of new applications. Almost all these new displays will be used for virtual displays: displays that are viewed within a few inches of the eye. Virtual displays can be hand-held, head-mounted, or body-worn. Although they are tiny, magnification optics produce a high-resolution virtual image that is similar to viewing a desktop monitor.
Kopin Corp. (Taunton, MA) recentl
y introduced a quarter-inch VGA, monochrome LCD that is just 0.24 inch diagonal. The
CyberDisplay
has an impressive 1700-dpi pitch, and the company plans to improve that to 2500 dpi by the end of the year. In Kopin's approach, electronics are fabricated on silicon, transferred to glass, and assembled using traditional crystal materials.
Haviland Wright, CEO of DisplayTech (Longmont, CO), says personal-information devices will have to be VGA resolution or better, because this will reduce the amount of scrolling people have to do when viewing information in a virtual display. "People don't want to scroll through information," says Wright. DisplayTech is now sampling a VGA-resolution display that has about 2000 dpi.
Siliscape (Palo Alto, CA), a Silicon Valley start-up, will soon begin sampling its new miniature display. The SVGA device will feature a 2500-dpi resolution and is packaged with a compound optical system that measures only 1.18 by 1.56 by 0.43 inches. "We have no pro
blem showing 10-point test on our displays," boasts Alfred Hildebrand, the president and CEO of Siliscape.
Both Siliscape and DisplayTech produce color images using field-sequential techniques. With this method, red, green, and blue LEDs are used to sequentially illuminate the display at approximately 180 frames per second. Both companies also feature a silicon electronics substrate on which a reflective layer and liquid crystal material are added. Therefore, the display operates in reflective mode. DisplayTech uses a ferroelectric liquid crystal, whereas Siliscape uses a polymer-dispersed liquid crystal.
Planar America (Beaverton, OR) is currently sampling a miniature display based on electroluminescent technology. Here, yellow-green phosphors are deposited on top of the active matrix, which is fabricated in silicon. Applying voltage causes the phospors to emit their own light. Densities of up to 1000 dpi are possible today, with 2000 dpi promised by the end of the year.
An explosion of new
wireless hand-held personal-information devices could be in the offing. By the end of the year, several wireless networks are expected to support data rates of 28.8 Kbps, enough bandwidth for many applications. Glen Kephart, Kopin's vice president of marketing for display products, says, "We think our displays have the visual quality, low power, and price points (under $30 each in volume) that will work for this market."
DisplayTech's Wright sees even bigger upheavals coming. "We may be at the beginning of a new phase, where convergence and hardware, like miniature displays, will drive product innovation." Many urge caution, however. Products that used earlier-generation mini displays have not fared well. Perhaps the higher densities offered by this new crop will make the difference.
Mini Displays Get Sharper Focus
