Nanosys is also hoping to spur big changes in another area: consumer electronics. Today’s computer-display manufacturers are limited by two factors. First, manufacturing the high-grade “single crystal” silicon used to make fast chips and processors is expensive and requires high temperatures, and the end product is too brittle to be layered onto large surfaces. Second, while so-called amorphous silicon-typically used in transistors that control whether display pixels are on or off-is easily and cheaply fashioned into thin-film electronics, it has slow electron flow and chews up a lot of power. Nanosys believes it can use nanotech to give the display industry the best of both worlds.
Nanosys is betting that the answer lies in nanowires-inorganic semiconductor structures only a few nanometers in diameter but up to hundreds of micrometers long. Pioneered by Charles Lieber, a chemist at Harvard and a scientific cofounder of Nanosys, nanowires are fast and efficient at moving electrons about. They can be used to create thin-film electronics with the performance of single-crystal silicon. Because their manufacture doesn’t require high temperatures, they can form high-performance electronics on plastic. And they’re cheap to make-like amorphous silicon.
In a first step toward making products for displays, Nanosys is assembling silicon nanowires en masse, using refined versions of techniques developed at Harvard and Berkeley. To grow the nanowires, automated systems control a series of chemical reactions in a vacuum-sealed gas chamber, depositing a “forest” of nanowires onto a glass surface. They harvest the nanowires and lay them down on plastic or glass in a continuous sheet. The aligned nanostructures are then connected to form transistors, using what Empedocles says are the same techniques used to pattern amorphous-silicon transistors.
If it works, this process could transform displays by allowing high-performance electronics to be spread over large areas, such as laptop screens. The result: better pictures and less battery drain. Laptop screens employing such nanowires will be faster and up to three times as energy efficient, says Empedocles. Since they will be made mostly of plastic instead of glass, they will also be lighter and more durable. Nanosys also envisions nanowire-based displays for personal digital assistants and cell phones. Currently, these devices can’t handle video, because the refresh rate of today’s small liquid-crystal displays is too low. With nanowire transistors, however, the screens could refresh much more quickly.
Eventually, nanowires could enable displays with built-in processors and memory, which would replace separate processing modules and hard drives. It’s a technical leap, one that will require making complex circuit patterns and data interfaces out of nanomaterials. But if it becomes feasible-and affordable-it could fundamentally change the devices that you use every day. “You can envision a substantial amount of logic on the display itself,” says David Mitzi, an expert on device electronics at IBM’s Watson Research Center. “You might have an interactive display or even a whole computer on a plastic sheet.”