Power converters are the systems that allow us to plug in our computers, lamps, and televisions and turn them on in a snap. Converters transform the alternating current (AC) that comes out of wall sockets into the exact level of direct current (DC) that the electronics need. But they also tend to lose, on average, up to 20% of their energy in the process.
Power converters work by using power transistors — tiny semiconductor components designed to switch on and off and withstand high voltages. A new transistor design — based on the application of nanoscale structures for high-voltage applications — means that much less heat is lost during the conversion process, making the transistors especially well-suited to high-power applications like electric vehicles and solar panels.
The heat dissipation in converters is caused by the high electrical resistance, among other factors, which is the biggest challenge in power electronic devices. This becomes even more of a problem in high-power applications. The higher the nominal voltage of semiconductor components, the greater the resistance. Power losses shorten the ranges of electric vehicles and reduce the efficiency of renewable energy systems.
The new transistor 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 more than 1,000 V.
The new technology incorporates two key innovations. The first involves building several conductive channels into the component to distribute the flow of current — much like new lanes added to a highway to allow traffic to flow more smoothly and prevent traffic jams. The 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 smart-phones and laptops — not in high-voltage applications. The researchers demonstrated nanowires with a diameter of 15 nm and a unique funnel-like structure, enabling them to support high electric fields and voltages of more than 1,000 V without breaking down.
Thanks to the combination of these two innovations, the transistors can provide greater conversion efficiencies in high-power systems. The prototype that was built using slanted nanowires performs twice as well as the best GaN power devices.