Simulation and Characterization of Cross-Turn-On Inside a Power Module of Paralleled SiC MOSFETs

Silicon carbide dice are often paralleled to realize power modules with high current rating. Owing to the large network of interconnect (parasitic) impedances, terminal waveforms could appear benign while the dice experience detrimental fault currents generated by spurious cross-turn-on. This paper will quantify the nonuniform distributions of current stress and switching energy among the dice, as well as the penalty caused by cross-turn-on, versus number of dice, gate resistance, input voltage, and switching current. A reliable model for the package is essential. This is demonstrated for a commercial power module with 16 dice, 124 layout inductances, and the companion parallel resistances extracted from the finite-element simulation. Modeling process to avoid convergence problem is developed and verified by the experimental results. For a module tested at 800 V/300 A and carrying six paralleled dice per switch, the cross-turn-on induced current spikes simulated without and with package model differ by as much as 11.75 times. Cross-turn-on increases the high-side switching energy and the total switching energy of the module by 44% and 20%, respectively. One-die, two-die, four-die, and six-die modules are constructed based on the asymmetrical layout to explore how the number of dice influences cross-turn-on and switching energy. Peak cross-turn-on current and total switching energy of the module increase with the number of dice. The peak cross-turn-on current and switching energy of the six-die module are 134% and 36% higher than those of the one-die module, respectively. Severity of cross-turn-on soars as the number of dice increases.