High-Voltage-Isolated Mems Quad-Solenoid Transformers with S-Shape SIO2 Isolation Barriers for Compact Galvanically-Isolated Gate Driver Applications

In this paper, we report high-voltage-isolated MEMS quad-solenoid transformers with ultra-thick SiO 2 isolation barriers that are wafer-level fabricated by MEMS and novel molten-alloy micro-casting processes. With 10µm-thick S-shape SiO 2 isolation barriers filled between the silicon-embedded primary and secondary coils, an over 2kV breakdown voltage is measured. Benefitting from the tight-coupled 3D quad-solenoid structure and the inserted magnetic core, a 743.2nH inductance and coupling coefficient of over 0.72 are reached. Owning to the tiny footprint of 6mm ² , one of the highest inductance integration densities of 123.9nH/mm ² is achieved. Furthermore, with over 1.4A saturation current and power transfer efficiency of 80% at a frequency of 3MHz, the proposed HV-isolated transformer chips cover most practical cases in high-efficiency high-voltage-isolated gate driver solutions and other future isolated integrated bias power supplies.