3-D electrothermal simulation of active cycling on smart power MOSFETs during short-circuit and UIS conditions

Active cycling of power devices operated in harsh conditions causes high power dissipation, resulting in critical electrothermal and thermo-mechanical effects that may lead to catastrophic failures. This paper analyzes the ageing-induced degradation of the chip metallization of a power MOSFET and its impact on the device robustness during short-circuit and unclamped inductive switching tests. A 3-D electrothermal simulator relying on a full circuit representation of the whole device is used to predict the influence of various ageing levels. It is found that ageing can jeopardize the robustness of the transistor when subject to short-circuit conditions due to the exacerbated de-biasing effect on the gate-source voltage distribution; conversely, this mechanism does not arise under unclamped inductive switching conditions. This allows explaining the difference in time-to-failure experimentally observed for the transistors subject to these tests and dissipating the same energy.