Germany’s Fraunhofer Institute for Applied Solid State Physics has demonstrated what it calls the world’s first monolithically integrated GaN half bridge for the 600 volt class. Half bridge circuits are the centerpiece of many voltage converters.

Monolithic integration combines several components on a single GaN chip, enabling small, powerful systems to be created. Monolithically integrated half bridge circuits also have better electronic properties. For example, the switching frequency can be improved by a factor of around 10 in comparison with conventional voltage converters.

“A switching frequency of up to 3 MHz allows us to achieve a much greater power density,” said Fraunhofer Research Associate Richard Reiner. “This is very important in areas such as e-mobility, where many converters which are as efficient as possible have to be fitted in very little space.”

Fraunhofer’s half bridge circuit comprises two GaN high electron mobility transistors (HEMT) and two integrated freewheeling diodes. The HEMTs have a breakdown voltage of more than 600 volts and an on-state resistance of 120 mΩ.

A folded chip layout enables the DC link capacitance to be tightly connected between the supply voltage and ground. This design creates an optimized power path and allows for clean, stable switching at high frequencies.

Even more complex circuits, such as a monolithically integrated multilevel inverter, have also been produced. Up to ten GaN power devices can be placed on one chip with an area of 2 x 3 square mm.

“This innovative approach brings a new level of power density, efficiency, robustness, functionality and reliability to e-mobility,” said Dr. Patrick Waltereit, Deputy Head of the Power Electronics business unit at Fraunhofer IAF.

Source: Fraunhofer Institute via Green Car Congress