Innovative nanotransistors that keep their cool at high voltages


  Matioli Elison

We have developed a transistor that can substantially reduce the resistance and cut the amount of heat dissipation in high-power systems. More specifically, it has less than half as much 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.

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, not in high voltage applications. At POWERlab we 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 findings were published in Nature Electronics in 2021.

The prototype we built using slanted nanowires performed twice as well as the best GaN power devices in the literature.

In a paper published in Nature Electronics in 2023, we have also shown that wide-band-gap Aluminium gallium nitride/Gallium nitride nanowires containing multiple two-dimensional electron gas channels can be used to create high-electron-mobility tri-gate transistors for power-conversion applications. The multiple channels lead to improved conductivity in the nanowires, and a three-dimensional field-plate design is used to manage the high electric field.

Power devices made with 15-nm-wide nanowires are shown to exhibit low specific on resistances of 0.46 mΩ cm-2, enhancement-mode operation, improved dynamic behaviour and breakdown voltages as high as 1,300 V.

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