Evaluation of a Nonlinear Resistive Polymer-Nanoparticle Composite for Field-Grading in a Double-Side Cooled 10-kV Silicon Carbide Rectifier Module

Abstract:
Packaging innovations are needed for medium-voltage silicon carbide power modules if the wide bandgap semicon-ductor is to expand into grid applications. This work explored the nonlinear resistive behavior of a polymer-nanoparticle composite for improving the insulation property of insulated-metal substrates in medium-voltage power modules. Electrical characterization of the composite found its electrical conductivity increasing nonlinearly with the electric field intensity at a switching field around 15 kV/mm. Coating the composite along the triple-point edges of a patterned alumina direct-bond-copper substrate increased the partial discharge inception voltage of the substrate encapsulated in a silicone gel by more than 80%. This improvement was unchanged after heating the coated substrate to 250 oC for 30 minutes. The finding opened the possibility for increasing the thermal performance of medium-voltage modules by using thinner direct-bond-copper substrates. For demonstration, a 10-kV silicon carbide diode module was designed and fabricated. Four 10-kV silicon carbide diodes were connected between two substrates with 0.5-mm thick alumina to form a full-wave diode rectifier. The triple-point edges of the patterned substrates were coated by the composite. The module functioned without partial discharge at a voltage near 10 kV. If the substrates were not coated, the module would require substates with 1.0-mm thick alumina to meet the insulation requirement.