Portland, Ore. - As flat-panel liquid-crystal displays made from amorphous silicon grow to gargantuan sizes, Hong Choi, chief technology officer at Kopin Corp., has an alternative display solution.
"At Kopin, we believe that mobile video will be really big-you already have television content available on cell phones, and portable media players can store three movies in a single gigabyte," Choi said. "The only thing that is missing is a way to view a really good, large-sized image without having to carry around a big monitor."
Kopin (Taunton, Mass.) offers OEMs tiny single-crystal silicon microdisplays that combine with a magnifying lens to project onto the retina an image that appears to be coming from 20- to 30-inch displays.
By eliminating the need to carry a life-sized display, the microdisplays offer mobile users of cell phones and media players the same resolution as large flat panels but in a package small enough to fit into a shirt pocket.
Today, LCD flat-panel displays are made from transparent amorphous silicon. But, because the material has low carrier mobility, it needs a large transistor size in order to be fast enough for refreshing.
By contrast, cell phone displays use transparent polysilicon transistors, which enable their smaller size. Viewing high-resolution images on such small screens, however, can't compare to the view provided by large, flat-panel displays.
Kopin's microdisplays, according to Choi, combine the best of both worlds-large virtual displays that are nevertheless a fraction of the size of a cell phone display. The trick is to use the high carrier mobility of single-crystal silicon to make diminutive-sized displays, but to magnify the image with a lens so that it can be viewed at a very large virtual size.
Microscope maker Scalar Corp. (Tokyo), for example, has combined one of its lenses with a Kopin microdisplay to project an image onto the retina that appears to be from a 28-inch display. Called Teleglass, the display attaches to any pair of eyeglasses and is so small that the user can still see around it to walk or even drive while simultaneously viewing the display.
Scalar's Teleglass display uses Kopin's standard 180k-pixel CyberDisplay, which measures 0.24 inch diagonally and provides a resolution of 800 x 225 pixels. Other Kopin models measure from 0.14 inch to 0.94 inch diagonally and have resolutions from 320 x 240 to 1,280 x 1,024 pixels. All of Kopin's displays require a lens to magnify the image so that it appears much larger to the user.
Like a normal semiconductor, the microdisplays are manufactured on a wafer-from single-crystal silicon. After fabrication, the top 200-nanometer layer of silicon is lifted off the standard silicon-on-insulator wafer and then sandwiched between two layers of glass. The display is then diced up like any other chip and illuminated with a traditional backlight.
Kopin's newest module is binocular, with two matched color displays for simultaneously projecting stereoscopic 3-D images directly onto both retinas. Choi sees a bright future for 3-D. It's "a vast potential market," he said, "such as for video games that combine a binocular 3-D display with head tracking so that you can turn your head to control [in] which direction you are looking."
Kopin's OEM evaluation modules are priced starting at $60. Predicting a further drop in price, Choi said that today Kopin's displays "are being marketed to end users for just a few hundred dollars. In a year or two, we think consumer eyewear prices will fall below $100."