The researchers used the counterintuitive approach of using nanoscale structures for high-voltage applications so that less heat is lost during the conversion process. This is usually a major challenge as the smaller the structures, the higher the electric field in high voltage switching and the higher the risk of breakdown and failure.
“We see examples of electric power losses every day, such as when the charger of your laptop heats up,” said Elison Matioli, a co-author of the paper in Nature Electronics and head of EPFL’s POWERlab. This becomes even more of a problem in high-power applications. “The higher the nominal voltage of semiconductor components, the greater the resistance,” he adds.
Power losses shorten the ranges of electric vehicles, for instance, and reduce the efficiency of renewable-energy systems such as solar cell inverters. Matioli, along with his PhD student Luca Nela and their team, developed a nanotransistor architecture with less than half as much resistance as conventional transistors while handling voltages of 1300 V.
The architecture uses several conductive channels to distribute the flow of current. “Our multi-channel design splits up the flow of current, reducing the resistance and overheating,” says Nela. The second innovation involves using nanowires made of gallium nitride. These have a diameter of 15 nm and a funnel-like structure enabling them to support high electric fields of 0.46 mΩ/cm2 and the 1.3kV voltage without breaking down.
“The prototype we built using slanted nanowires performs twice as well as the best GaN power devices in the literature,” said Matioli. He doesn’t see any major obstacles to large-scale production of the nanotransistor technology. “Adding more channels is a fairly trivial matter, and the diameter of our nanowires is twice as big as the small transistors made by Intel,” says Matioli. The team has filed several patents for their invention.
Matioli says several major manufacturers have expressed interest in teaming up to further develop the GaN nanotransistor technology.