Size Matters

So far, the smallest structure produced using this method is about 10 micrometers across. That's 50 times fatter than the finest features produced using conventional photolithography. But that's okay, since these electronics are not designed for devices that require high density, like memory chips or microprocessors.

"There are a lot of applications, like your cell phone or PDA, that need transistors that can be spread over a large surface area, and that is what we can make cost-effectively," says Sauvante.

He proudly unpacks the company's demo unit: a plastic square bearing one of Rolltronics's transistors, attached via alligator clips to a small, gray box. The box sends a periodic charge to the transistor's "gate" layer, allowing current to flow from one of the transistor's terminals to the other. When this current returns to the box, it's amplified and used to turn a red light-emitting diode on and off.

As a display of computational power, it isn't exactly stunning, but it does prove that Rolltronics' transistor can-like all transistors-act as a switch, clearing the way for the manufacture of more complicated silicon-on-plastic structures. "Inside of two years from now we'll be shipping products based on this technology," Sauvante predicts. The first of these will likely include backplanes for organic light-emitting displays and electronic paper systems such as those under development at Cambridge, MA-based E Ink and Palo Alto, CA-based Gyricon Media.

Rolltronics isn't the only company trying to bring flexible transistors to market (see "Flexible Transistors"). Bell Labs, for example, has developed a system for printing multi-layered plastic transistors on small sheets of flexible polymer using a finely patterned rubber stamp. And Lucent has fused Bell Labs' printed transistors with sheets of electronic ink from E Ink to demonstrate a working electronic paper prototype.

But Sauvante contends that because Bell Labs' transistors are themselves made of plastic, "they'll never be capable of reaching the switching speeds of silicon." Rolltronics' silicon-on-plastic circuits, he says, are "the only viable approach" for making integrated e-paper devices where the display, the backplane, and high-speed drive electronics-such as analog-to-digital converters and row- and column-drivers-are all flexible.

Sauvante's enthusiasm about Rolltronics' technology has begun to spread. "What they are doing is very, very promising, and it looks to me like it has a very high probability of success," says Nicholas Sheridon, director of research at Gyricon Media. "And if it does succeed, it could have a very big effect on making transistor arrays more available to people, for things like displays."