Combined geometrical techniques and applying nonlinear field dependent conductivity layers to address the high electric field stress issue in high voltage high-density wide bandgap power modules

Abstract

Wide bandgap (WBG) power modules made from materials such as SiC and GaN (and soon Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and diamond), which can tolerate higher voltages and currents than Si-based modules, are the most promising solution for reducing the size and weight of power electronics systems. In addition to the higher blocking voltages of 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 μm (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 testing samples under manufacturing/factory conditions and with high-quality materials. Thus, it is difficult to determine the efficacy of electric field and PD control methods. To address this issue, an electric field criterion based on precise dimensions of a power module and its PD measurement is introduced. Then, combined geometrical techniques and the application of nonlinear field-dependent conductivity (FDC) layers are proposed, for the first time, to address the high electric field issue in an envisaged 25 kV high-density WBG power module. Electric field modeling and simulations are carried in COMSOL Multiphysics where various electric field reduction methods proposed in this paper can be used as a guideline and reference to design the insulation system for next-generation WBG power modules, meeting both the one-minute insulation and PD tests based on IEC 61287-1.