Paul Bergstrom works in the clean room in the Microfabrication Facility.
Paul Bergstrom works in the clean room in the Microfabrication Facility.

Electron Transistors Turn Up the Heat

by Marcia Goodrich

In From the Cold

Electrons can be intractable little subatomic particles, which is why researchers sometimes have to dunk them in liquid helium to make them behave. Paul Bergstrom's team is only the second research group in the world to build the device known as a single electron transistor that minds its manners at room temperature.

The transistors vary in size; the smallest is not quite 20 nanometers across. Line up 12,500 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 about 8 nanometers wide and 4 nanometers thick, carefully deposited using a beam of gallium ions. "Each dot is a 3-D hemisphere," 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 can have multiple levels of logic," Bergstrom said, not just two. "Instead of having zero and one, you can have zero and two, zero and three, and so forth," he says. The power of electronic devices would increase significantly.

Ultimately, single electron transistors could be incorporated in a new generation of nanoscale electronic devices, either by integrating them with the current technology or by replacing it. 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."

"It could open up whole new aspects of electronics," he says. In particular, he is working with Michigan Tech's Multiscale Technologies Institute to develop sensors that could detect an array of chemicals, from pollutants wafting out of a coal-fired electrical plant to agents used in biological and chemical warfare.