High Efficiency on Si-Integrated Microtransformers for Isolated Power Conversion Applications

This paper details the design, fabrication, and characterization of silicon-integrated microtransformers for isolated bias supplies. Racetrack-shaped microtransformers were designed and fabricated using the advanced double-layer metal (DLM) microfabrication process. The DLM devices have high inductance density of more than 80 nH/mm² with an efficiency of approximately 78.2% at 20 MHz at 0.5-W output. This is the highest efficiency and power density reported for an integrated transformer in the literature. The inductance drop is less than 20% with a bias current of 0.35 A with up to 6-kV dc breakdown voltage achieved.