Energy-efficient power electronics for energy conversion and transmission are becoming increasingly important, as future-oriented and sustainable energy concepts, such as electric mobility or power supply via renewable energies, depend on them. For many years, power semiconductors have been used in power converters. But it is not only the semiconductor material itself that make the difference, but also the packaging and the design of the components. Because the more compact and more efficient the packaging is, the more resource-efficiently they work. However, a compact system design is often difficult to implement with the discrete components that dominate the GaN power electronics market. Most of the time, the critical loops between transistors and the supply rails have to be individually designed and wired as circuits from discrete components.
A user-friendly alternative is now offered by scientists of the Fraunhofer-Institute for Applied Solid State Physics IAF in Freiburg, Germany. They have embedded their gallium nitride-based integrated power circuits (GaN Power ICs) as a half-bridge in a printed circuit board (PCB) which features all critical wiring, including gate and DC link capacitors, within the package. Due to the scientists, the result is an extremely compact and efficient power converter suited for all 600 volts applications. It allows a modular system design, thus facilitating design and manufacturing processes.
Monolithically integrated GaN Power ICs
The Fraunhofer IAF has many years of experience in the monolithic integration of power electronic GaN chip technologies. Last year, in the course of the GaNIAL research project, the scientists from Freiburg managed to monolithically integrate current and temperature sensors, 600 V power transistors, freewheeling diodes and gate drivers in a single GaN power IC. The semiconductor material gallium nitride was deposited on low-cost silicon substrate (GaN on Si), making the chip technology suitable for cost-efficient mass manufacturing, and therefore very attractive to industry.
The integration density of the GaN Power ICs of Fraunhofer IAF not only enables a higher switching frequency and therefore a higher power density than comparable circuits, but also higher reliability and compactness due to the integrated sensor technology. With their GaN power ICs in a half-bridge configuration, the researchers have already achieved efficiencies in DC-DC converters of over 98.8 percent at 350 V, and have demonstrated a high switching frequency of 40 MHz in continuous operation at 250 V and resonant operation.
Highly integrated half-bridge circuits via PCB embedding
“GaN-on-Si technology allows monolithically integrated circuits for half-bridge converters, but does not solve the wiring problem to external capacitors”, says Stefan Mönch, researcher at Fraunhofer IAF. He adds: “However, these critical connections to gate drivers and DC-link capacitors are essential for clean and efficient switching behavior. With our goal of a perfect power converter in mind, we were looking to find the optimal highly integrated packaging technology for our GaN Power ICs”. For this purpose, he and his team processed their ICs with a thick copper electroplating on both sides, making them suitable for PCB embedding.
This adaptation of the metallization made it possible for the company Würth Elektronik CBT to build the chips using their embedding technology ET Microvia suitable for series production. Together with the project partners Bosch and the University of Stuttgart, the researchers were able to design a PCB package that is only 12 mm wide and 0.4 mm flat. It integrates two monolithic GaN power ICs as a half-bridge configuration and provides the critical decoupling capacities for the gate driver and DC link capacitors already on the package.
The embedding technology eliminates the need for bonding wires, which also minimizes parasitic inductances. The critical connections between GaN IC and capacitors are thus already optimized and no longer need to be elaborately designed by users. The result is a user-friendly solution that provides all critical components of a voltage converter already optimized in one package.