A switching frequency of up to 3 MHz allows us to achieve a much greater power density. 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.

—Richard Reiner, research associate at Fraunhofer IAF in the Power Electronics business unit

Monolithically integrated half bridges are more compact, are easier to assemble and improve reliability.

Fraunhofer IAF’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. The operation of this circuit was demonstrated at the 4^th IEEE Workshop on Wide Bandgap Power Devices and Applications (WiPDA) in a down converter from 400 to 200 volts at a switching frequency of 3 MHz.

Even more complex circuits, such as a monolithically integrated multilevel inverter, have already been produced using this GaN-on-Si technology. In this topology, ten GaN power devices are placed on one chip with an area of 2 x 3 mm². Each switch has a breakdown voltage of 400 volts in off state and a resistance of 350 mΩ in on state.

Compared with conventional converters, multilevel inverters generate less noise during DC/AC conversion. This means that they require smaller output filters. Monolithic integration therefore not only reduces costs, but also makes voltage converters more compact and lightweight. This converter was demonstrated in inverters operating at the grid voltage level used in the US (120 volts).

Covering long distances without generating any emissions requires not only powerful batteries but also the development of lightweight electric cars which generate as little energy as possible. This can only be accomplished using electronic components based on semiconductor materials such as gallium nitride (GaN), which in contrast to silicon carbide (SiC) can be grown as epitaxial layer on cost-effective, large area silicon substrates. When used to produce electronic components for electric vehicles, GaN enables higher power densities to be achieved more energy efficiently. The aim of car manufacturers and users is to develop extremely efficient on-board chargers for electric vehicles which take up as little space as possible.

Their compact design minimizes negative influences such as line impedances, improving the electrical switching characteristics. The integration of additional sensor technology, such as a thermal monitoring system, improves operation even further.

This innovative approach brings a new level of power density, efficiency, robustness, functionality and reliability to e-mobility.

—Dr. Patrick Waltereit, deputy head of the Power Electronics business unit at Fraunhofer IAF

Fraunhofer IAF is presenting its monolithically integrated half-bridge circuit at PCIM Europe in Nuremberg, 16-18 May 2017.