Characterization of Nonlinear Field-Dependent Conductivity Layer Coupled With Protruding Substrate to Address High Electric Field Issue Within High-Voltage High-Density Wide Bandgap Power Modules

Abstract

In addition to higher blocking voltages of wide bandgap (WBG) power modules, their volume has been targeted to be several times smaller than that of Si-based modules. This translates into higher electric stress within the module and, in turn, a higher risk for unacceptable partial discharge (PD) activities, leading to aging and degradation of both the ceramic substrate and the silicone gel. Due to the small dimensions of power module geometry, in the mm- or $\mu \text{m}$ (for protrusions)-range, and due to its extremely non-uniform electric field geometry, conventional high-voltage testing electrode geometries cannot simulate real conditions. On the other hand, university-based laboratories often cannot provide manufacturing/factory conditions for testing samples and for high-quality materials. Thus, it is difficult to determine the efficacy of electric field control methods through experiments. In these situations, numerical electric field calculation is the only feasible way to evaluate different electrical insulation designs. To this end, the finite-element method (FEM) models of the electrical insulation system used in WBG power modules are developed in COMSOL Multiphysics. It is shown that the current geometrical techniques alone cannot address the high-electric field issue within high-density WBG modules. To address this issue, for the first time, nonlinear field-dependent conductivity (FDC) materials applied to high-electric stress regions in combination with a recently introduced geometrical technique known as the protruding substrate is proposed. In this regard, the nonlinear FDC layer is characterized and various designs to reduce the electric field are evaluated. Moreover, the effect of the operating frequency on the performance of the solution mentioned above will be studied.