A Comprehensive Study on Electric Field Coupling Effects of Medium-Voltage SiC Power Module and Optimization Design

Insulation ability is critical essential for long-term operation of medium-voltage power modules, which is strongly affected by the internal electric field concentration at insulation weak points. This paper establishes a comprehensive study on the electric field coupling effects of power module considering the interaction between silicon carbide (SiC) chip and package structure. Technology computer-aided designer (TCAD) simulation is carried out to analyze the insulation weak points under high DC voltage stress, resulting that electric field concentration at the interfaces between the encapsulation material and the termination region as well as the die outer edge with the maximum electric field strength value of nearly 2.0×10⁷ V/m contribute most to the insulation degradation of power module. Optimization design is therefore proposed and verified by simulation to enhance the insulation ability by coating polyimide on the surface of chip and DBC. Finally, five types of 10 kV SiC power modules of whether optimization design is added are fabricated and partial discharge (PD) test is conducted to verify the coupling effects between chip and package as well as the insulation improvement of optimization design, resulting in the apparent charge of only 1.16 pC and only one PD pulse beyond 10 pC under 8.5 kV DC stress through optimization.

I. Introduction

As one of the wide-band-gap semiconductor devices, medium-voltage level silicon carbide (SiC) MOSFET based power modules hold the advantages of high voltage blocking capability, low on-state resistance and high switching speed, illustrating broad prospects in various medium-voltage application [1] [2] fields such as ultra-high voltage power transmission, high-speed railway and solar/wind inverters.