From Michigan Tech Today Septermber 22, 2005

Just when you thought cell phones couldn't (or shouldn't) get any smaller, Paul Bergstrom predicts that pretty soon you'll be slipping one into your wallet alongside your driver's license.

"I can see the day when cell phones are as thin as a credit card," says Bergstrom, an assistant professor of electrical and computer engineering.

Bergstrom is working on developing nanoscale electronic devices. It's not just a matter of making things littler. They will also be able to do lots more stuff, or, as Bergstrom says, "They can be integrated in smaller packages with more functionality."

To accomplish this, Bergstrom is working on developing the smallest switch ever: a single electron transistor.

"It could open up whole new aspects of electronics," he says. "A single electron transistor is a quantum device--it has very peculiar behavior."

The transistor is about 100 nanometers across. Line up 2,500 of them and they'd be about as long as a human hair is wide. And on each transistor is a series of quantum dots. "Each dot is a 3D hemisphere under 10 nanometers across," Bergstrom explains. "Electrons are trapped on that dot."

Transistors work by having their gates open or shut to an electric current, creating the zeros and ones upon which all digital life depends. Quantum dots could change all that. By manipulating the potential energy of the electrons on each dot, "you could have multiple levels of logic," Bergstrom said, not just two. "Instead of having zero and one, you could have zero and two, zero and three, and so forth," he said. The power of electronic devices would increase significantly.

That said, these nano-transistors have one minor drawback. They only work at nano-temperatures. "We have to cool them to 4 degrees Kelvin," Bergstrom says. That's accomplished by immersing them in liquid helium, which could be inconvenient for the average cell-phone user.

Thus, with funding from the Defense Advanced Research Projects Agency and the Army Research Lab, Bergstrom and his team are working to make single electron transmitters that work at room temperature.

The colder they are, the more tractable electrons become, and moving them around precisely at warmer temps is a big hassle. "The formation of these ultra-small quantum dots is very difficult," Bergstrom said. "We're trying to engineer them with an ion-beam etching tool, to put each particle exactly where it should be."

"This is an area with great potential," he added. "It could open up whole new aspects of the electronics industry."