Researchers at the Fraunhofer-Institute for Applied Solid State Physics IAF have worked with Würth to embed monolithic GaN power chips into a PCB as a half bridge that includes the gate and DC link capacitors.
The result is an extremely compact and efficient highly integrated 600V voltage converter with a modular design that sets the benchmark for the proposed GaNext project in the UK: PROJECT FOR WORLD’S MOST COMPACT 650V MODULE
The team in Freiburg developed a monolithic GaN-on-Si chip as part of the GaNIAL research project last year: SINGLE CHIP INTEGRATES SENSORS FOR THE FIRST TIME
This combines current and temperature sensors, 600 V power transistors, freewheeling diodes and gate drivers in a single GaN device. The gallium nitride was deposited on low-cost silicon substrate (hence GaN-on-Si), making the chip technology suitable for cost-efficient mass production on mainstream high volume silicon processes.
Earlier this year EPC shbowed the first commercial monolithic GaN chip to combine the power transistor and driver: FIRST MONOLITHIC FET AND DRIVER CHIP
The monolithic integration enables a higher switching frequency alongside the higher reliability and compactness from the integrated sensor technology. With the GaN chip n a half bridge icircuit, the researchers have already achieved a DC-DC converter efficiency over 98.8 percent at 350V, and have demonstrated a high switching frequency of 40 MHz in continuous operation at 250 V and resonant operation.
“GaN-on-Si technology allows monolithically integrated circuits for half bridge converters, but does not solve the wiring problem to external capacitors,” said Stefan Mönch, researcher at Fraunhofer IAF. “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 voltage converter in mind, we were looking to find the optimal highly integrated packaging technology for our GaN power ICs.”
To embed the chip in a PCB, he and his team processed the chip with a thick copper electroplating on both sides. This metallization allowed Würth Elektronik CBT to build the chips using microvia embedding technology for series production.
Next: GaN-on-Si PCB
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 devices as a half bridge and provides the critical decupling 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 result is a user-friendly solution that provides all critical components of a voltage converter already optimized in one package.
Fraunhofer IAF is showing the design at PCIM this week. The GaN power IC is also part of a presentation by Dominik Koch (University of Stuttgart) at the PCIM Europe conference.