High Dielectric Constant and High Dielectric Strength Polymer Coating for Electric Field Mitigation in 15 kV SiC MOSFET Power Modules

Medium voltage (MV) silicon carbide(SiC) power devices are on the rise and are expected to be applied in power grids, high-voltage pulse power supplies, and other applications. However, the contradiction between high insulation voltage and high power density of power modules requires new insulating materials to alleviate. Compared to the traditional approach of using composite material to increase the dielectric constant, this paper introduces a single homogeneous material polymer coating with high dielectric constant and high dielectric strength, and demonstrates that this coating can reduce the maximum electric field of silicon gel within the module. The electrical properties of the coating were measured, characterizing its high dielectric constant and high dielectric strength compared to common polymer materials. Electric field simulation shows that the coating can reduce the maximum electric field strength in the silicon gel by 57%. After process stabilization, the coating thickness can be guaranteed to be approximately 80 μm, applied along the triple point edge on direct bonding copper(DBC) for 15kV module applications. The partial discharge inception voltage(PDIV) of the coating DBC in the silicon gel was measured. Compared to the uncoated DBC, the PDIV of the coated DBC in the silicon gel increased by an average of over 101%. The effectiveness and compatibility of the coating were demonstrated through a double pulse test(DPT) using the same DBC packaged 15kV module under a 12kV bus voltage, providing an economical and efficient solution for the insulation of high power density MV power modules.