The Invisible Computer

Here's an interesting piece by Wil McCarthy on Transparent thin-film transistors, or TTFTs, that appeared in the July issue of WIRED.


For all practical purposes, silicon used to be the only real option for making integrated circuits. Sure, you could use exotic semi­conductors, like germanium, or expensive organic polymers. But for reasons of economics and reliability, to produce the zillions of transistors at the heart of every electronic gadget, silicon was it. Specifically, silicon with its atoms arrayed into an elegant crystal pattern.

Not anymore. Researchers have invented a semiconductor with conductivity similar to silicon. It makes cheap transistors that are as heat-resistant as stoneware, which means they can survive in hostile environments like car engines. They're as flexible and durable as plastic garbage bags, an obvious plus for portable electronics. The best part: They could be used in 3-D displays and windshield computers. Why? Because they're utterly clear.

Transparent thin-film transistors, or TTFTs, are a mixture of zinc and tin oxides. Ordinarily, if you wanted to turn that material into the crystals computer scientists like, you'd use precise combinations of pressure, tem­perature, and flow rate to deposit it on glass. It's an expensive, slow process. But John Wager, a computer engineer at Oregon State University, has figured out a way to spray microscopic blobs of TTFT almost like an aerosol. The resulting layer is "amorphous" - that is, the atoms are distributed randomly instead of as a crystal. Yet Wager's TTFTs transfer electrons 10 times faster than, say, amorphous silicon, and they can carry and process more infor­mation. Chip fabrication temperatures often exceed 1,000 degrees Fahrenheit; Wager's "sputtering" process works below the boiling point of water, which means he can spray TTFTs onto plastic without it melting. That provides a flexible, durable substrate that's more see-through than window glass.

For people interested in computer chips, those specs couldn't sound better. OSU investors, including the Army Research Office and Hewlett-Packard, and potential customers like Darpa and the Department of Energy, all see a host of possible applications. Fabricating TTFT chips, says Wager, could be 1,000 times cheaper than silicon. "I envision an industry of niche cottage fabs," he says, "making transistors with specialty functions."

Like what? Once the first circuits made from wide bandgap semiconductors hit the mass market, the fact that they're transparent will be hard to overlook. "Window glass is wasted real estate," Wager says. "TTFTs could be used for displays, for security electronics." They'll integrate smoothly with optic fiber and standard metal wires. See-through semi-conductors could even make it possible to etch circuitry rapidly in three dimensions, on the inside of clear solid objects. Theoretically, a femto­second-pulse laser - which can blast electrons away from molecules with a finely focused sunlike flash, altering the composition of materials such as glass and plastic - could draw a 3-D supercomputer inside a transparent semiconductor.

Imagine a video pillar filled top to bottom with radiant 3-D pixels, or a heads-up windshield display that helps you navigate, blocks the sun, flashes warnings to other drivers, and lights up the road ahead. Imagine eyeglasses with the computing power of a high-end laptop and the resolution of HDTV. "The military will get first crack at that kind of tech in five to ten years," Wager says. Consumers can expect clear iPods by 2020, and supercomputing soda bottles sometime thereafter.