Kopin's Competition
PC Magazine via Individual Inc. :
Display manufacturers exploring the potential of micropanel technology for a new generation of displays are finding that micropanels may hold the key to lightweight yet affordable desktop and projection displays.
LCD Limitations
Manufacturers of conventional liquid crystal displays are busy building larger flat panels, but problems are getting in the way. The relatively large transistors required at each pixel location block a significant portion of the transmitted light, requiring the use of brighter--and more power-hungry--back lights. Higher resolutions require more transistors per panel, which increases the problem of getting an adequate yield from production lines to make the end product affordable.
Another limitation: LCD technology doesn't always scale up to larger sizes reliably or smoothly, making it more costly to build larger panels. Last year, the world's LCD production capacity was effectively cut in half when demand for larger panels meant that displays could be made only two at a time, instead of the four-at-a-time methods that could be used for smaller panel sizes.
Reflective Riches
In contrast, micropanels hold great promise. They're made using standard fabrication techniques, making them inexpensive to build. One manufacturer estimates that costs could be as little as $30 per half-an- inch of display panel, in large quantities. Reflective technology allows more light from the source to project through to the user's eyes. With projection designs, the image can be made just about any size you want, from head-mounted "deskless" displays to boardroom screens.
Three manufacturers are taking different approaches to reflective
micropanel technology. The leader is Texas Instruments' Digital Light
Processor (DLP), based on a micromirror design. Using tiny square mirrors mounted on diagonal hinges, each mirror can be positioned to reflect light through or away from the projection optics. Projectors with 800-by-600 resolutions are already on the market.
Twice as Bright
A joint project between Hitachi and Raychem Corp. has created LCD fixed-mirror technology, which the companies estimate can be two to three times brighter than traditional LCD projectors. The companies say that fixed-mirror panels can produce up to 5 lumens per watt, compared with 1 to 2 lumens per watt for conventional designs.
Standard LCDs use a layer of liquid crystal material to twist light so that it then can be blocked or transmitted by polarizing filters. These filters are one of the main reasons that so much transmitted light is consumed by a typical LCD panel. The LCD fixed-mirror design encapsulates drops of the liquid crystal material in plastic polymer material. In an "on" state, the crystals line up vertically, letting light pass through the layer. When "off," the crystals arrange themselves randomly, scattering light rather than letting it pass. This design doesn't require polarizing layers, and it doesn't require the special alignment layers or spacers used in standard liquid crystal panels.
The encapsulated liquid crystal material is coated onto a glass surface and then bonded to a semiconductor substrate. This substrate is covered with reflective aluminum mirrors, along with small transistors used to switch the encapsulated liquid crystals on and off. The resulting panel is far brighter than traditional LCD panels for a number of reasons. More than 90 percent of the panel's surface is reflective, compared with smaller aperture ratios found in traditional LCD designs. And without relying on polarizing layers,
more of the light is transmitted through the thin layer of encapsulated liquid crystal.
Rapid-Response ChronoColor
Displaytech, a new company from Boulder, Colorado, has developed another reflective micropanel design, called ChronoColor. This panel uses standard fabrication techniques, and the reflective surface of the semiconductor serves as an electrode for the display cell. The cells use a thin layer of ferroelectric liquid crystal material--about one-fifth to one-eighth the thickness of a standard LCD panel--that provides fast switching. This design makes it possible to create pixels as small as 10 microns square, which means that you could create a 1,024-by-768 display on a chip less than a half an inch wide.
Unlike some designs that use colored filters and three or four cells per pixel, the ChronoColor panel uses only one cell per pixel. The entire panel is illuminated in sequence by red, green, and blue light sources. These three images are created so rapidly that the user's brain combines them to create a full-color image. ChronoColor panels have been demonstrated using red, green, and blue LEDs as the illumination source, resulting in a display well suited for head-mounted displays or viewfinders. Other light sources could be used, depending on the application.
The ChronoColor's method of illumination requires extremely fast cell switching. To create a 60-Hz image, the cells must be able to switch off or on at least 180 times per second. The ferroelectric liquid crystal used in the micropanel design provides this rapid response. Based on a look at the prototype ChronoColor panels, this single-cell-per-pixel design works extremely well. Instead of the grainy image seen with some traditional LCD panels using separate color cells, the ChronoColor image is much smoother and sharper. There's also far less of a "screen door" effect with the
ChronoColor display, because the individual cells have much less space
between them than do the cells of traditional LCD panels.
It's too early to tell which of these three will be a winner in the
marketplace, but micropanels make the future of personal computer displays looks bright and affordable.
Alfred Poor, PC Magazine
[07-27-96 at 11:24 EDT, Copyright 1996, Ziff-Davis Wire, File: c0726229.2zf] |
