ICs Built at -234 ºF

Physicists at UC San Diego have successfully created speedy integrated circuits with particles called “excitons,” which operate at commercially cold temperatures. This development brings closer to reality the possibility of a new type of extremely fast computer based on such particles.

Their discovery follows the team’s demonstration last summer of an integrated circuit – an assembly of transistors that is the building block for all electronic devices – capable of working at 1.5 K above absolute zero. (See: First Excitonic ICs Built.) That temperature, equivalent to -457 °F, is not only less than the average temperature of deep space but is also achievable only in special research laboratories.

Now the scientists report that they have succeeded in building an integrated circuit that operates at 125 K, a temperature that, although a chilly -234 °F, can still easily be attained commercially with liquid nitrogen, a substance that costs about as much per liter as gasoline.

“Our goal is to create efficient devices based on excitons that are operational at room temperature and can replace electronic devices where a high interconnection speed is important,” said Leonid Butov, a professor of physics at UCSD and the research team’s leader. “We’re still in an early stage of development. Our team has only recently demonstrated the proof of principle for a transistor based on excitons, and research is in progress.”

Alex High and Aaron Hammack adjust the optics in their UCSD lab. (Image: University of California, San Diego)

Excitons are pairs of negatively charged electrons and positively charged “holes” that can be created by light in a semiconductor such as gallium arsenide. When the electron and hole recombine, the exciton decays and releases its energy as a flash of light.

The fact that excitons can be converted into light makes excitonic devices faster and more efficient than conventional electronic devices with optical interfaces, which use electrons for computation and must then convert them to light for use in communications devices.

“Our transistors process signals using excitons, which, like electrons, can be controlled with electrical voltages but, unlike electrons, transform into photons at the output of the circuit,” Butov said. “This direct coupling of excitons to photons allows us to link computation and communication.”

Other members of the team involved in the discovery were physicists Gabriele Grosso, Joe Graves, Aaron Hammack and Alex High at UC San Diego, and materials scientists Micah Hanson and Arthur Gossard at UC Santa Barbara.

Their research was supported by the Army Research Office, the Department of Energy and the National Science Foundation. Details of the study appear in the online issue of the journal Nature Photonics.

For more information, visit: http://www.ucsd.edu/