19. Mai 2021, 17:11 Uhr | Ralf Higgelke
Based on two innovations, a team at EPFL has developed nanotransistors made of gallium nitride for high-power applications that can withstand more than 1000 V. This could be used, for example, to extend the range of electric vehicles. This could, for example, extend the range of electric vehicles.
The objective of a team of engineers at EPFL is to develop novel power transistors to increase the efficiency of power converters. With their completely new transistor design, based on the counter-intuitive use of nanoscale structures for high-voltage applications, losses decrease during conversion, making the transistors particularly suitable for high-power applications such as electric vehicles and solar cells.
The heat dissipation in converters is caused by the on-resistance of the transistor, among other factors. “The higher the nominal voltage of semiconductor components, the greater the resistance,” says Elison Matioli, a coauthor of the paper and head of EPFL’s POWERlab. Power losses shorten the ranges of electric vehicles, for instance, and reduce the efficiency of renewable-energy systems.
Matioli, along with his PhD student Luca Nela and their team have developed a transistor that has only half as much on-resistance as conventional transistors, while holding voltages of over 1,000 V. The EPFL technology incorporates two key innovations.
The first involves building several conductive channels into the component so as to distribute the flow of current – much like new lanes that are added to a highway to allow traffic to flow more smoothly and prevent traffic jams. “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, a semiconducting material ideal for power applications. Nanowires are already used in low-power chips, such as those in smartphones and laptops, but not in high voltage applications. The POWERlab demonstrated nanowires with a diameter of 15 nm and a unique funnel-like structure enabling them to support high electric fields, and voltages of over 1,000 V without breaking down.
Thanks to the combination of these two innovations – the multi-channel design that allows more electrons to flow, and the funnel structure that enhances the nanowires’ resistance – the transistors can provide greater conversion efficiencies in high-power systems. “The prototype we built using slanted nanowires performs twice as well as the best GaN power devices in the literature,” says Matioli.
While the engineers’ technology is still in the experimental phase, there shouldn’t be any major obstacles to large-scale production. “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.
Demand for chips that can perform efficiently at high voltages is set to boom as electric vehicles become more widely adopted, since more efficient chips translate directly into longer ranges. Several major manufacturers have expressed interest in teaming up with Matioli to further develop this technology.
L. Nela, et al., Multi-channel nanowire devices for efficient power conversion, Nat Electron 4, 284–290 (2021). https://doi.org/10.1038/s41928-021-00550-8