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.