Electrothermal effects during unclamped inductive switching (UIS) of power MOSFET´s

The ruggedness of scaled power DMOSFET´s under unclamped inductive switching (UIS) conditions is studied using an advanced two-dimensional (2-D) device simulator. It is shown that at the onset of device turnoff, significant self-heating occurs within the intrinsic device which leads to an increase in the avalanche breakdown voltage of the device. The self-heating mechanism is incorporated by self-consistently solving heat generation and diffusion equations with semiconductor charge balance and transport equations. The power module is modeled by accounting for various thermal resistances including those contributed by the package, contact metallization and intrinsic device material. The simulation results are compared with extensive UIS measurements and it is shown that the simulations can be used to identify local “hot spots” and the design and process parameters that lead to thermal runaway