Finite-Element Analysis of Coupled Electro-Thermal Problems With Strong Scale Separation

We present a finite-element analysis of the coupled electro-thermal behavior of a mm²-sized power DMOS device, with a focus on resolving μm-sized structures. For a reliable power technology, the predictions of current and temperature distributions under self-heating are vital for reaching long device lifetime. Two aspects of our approach are unique: First, we have integrated the active region of the DMOS into the finite-element program code as a nonlinear voltage and temperature dependent tripole, incorporating local biasing and temperature conditions. Second, to model small features like defects or process-induced imperfections in sufficient detail, we use the Nitsche-type nonmatching grid technique to include the substantially finer meshed microscale geometry. This allows us to study very local changes in temperature and biasing conditions, which are normally not accessible. The methodology is applied to a state-of-the-art power technology device with integrated current sensor to validate the methodology. Good agreement is found between results and experiments.