Power MOSFET RDSon under repetitive avalanche cycling

In this paper, a low voltage vertical power MOSFET is submitted to repetitive avalanche cycles under very high current (>400A) at high temperature (>150degC). Electrical characteristics such as B_VDSS, I_GSS, I_DSS, V_F, V_GSth and R_DSon are systematically tested along cycling. After a large number of avalanche pulses well above products requirements measurements show that R_DSon decreases with the number of avalanche cycles whereas other parameters stay constant. With a simple model of R_DSon measurement and new measurements such as the resistance of the metallization between two bonding wires we can connect this unexpected drop of R_DSon measurement to MOSFET source electrode evolution.