Failure mechanisms of low-voltage trench power MOSFETs under repetitive avalanche conditions

In this paper we present a mechanism leading to early fails in a trench power MOSFET when operated at high drain currents under repetitive avalanche conditions (also referred to as “unclamped inductive switching”). While typical fails show burn marks at (or under) the bond stitches, early fails can occur close to the active area´s edges or corners. With plausible assumptions both cases can be consistently explained by thermal runaway as demonstrated by electrothermal simulation.