Study of mechanical stress impact on the I–V characteristics of a power VDMOS device using 2D FEM simulations

Reliability is a major economic and technical challenge for power electronics dedicated to embedded applications (avionics, automotive, hybrid vehicles, etc.). As the damage in a power assembly is essentially due to thermo-mechanical stress resulting from temperature variations (ambient and junction) [1], industrial actors ask for integrated devices allowing anticipation of the failure by monitoring temperature and mechanical stress. Power devices I(V) characteristics depend on the mechanical stress. Hence, one can make use of this dependence to assess the mechanical stress values from the electrical characteristics of the device. The extracted mechanical stress values give information on the mechanical state of the power module that one could exploit to anticipate failure. To study the impact of the mechanical stress on the I(V) characteristics, we carry out mechanical simulations using a finite element method (FEM) simulator (COMSOL) for a simple 2D power assembly to calculate the mechanical stress at different temperatures as well as the mechanical stress due to an external strain. The calculated values are then fed into a FEM physical device simulator (Sentaurus TCAD) to determine the electrical characteristics of a VDMOS device at different temperatures. A dissociation of mechanical stress and thermal effects on the VDMOS I(V) characteristics would make it possible to have a graphical representation that could be used to have a quick estimate of the mechanical state of the power VDMOS through its electrical characteristics.