VDMOS electrical parameters potentially usable as mechanical state indicators for power VDMOS assemblies

Power device reliability is a multidisciplinary domain. It requires design and integration of sensors, implementation of signal processing algorithms that allow processing the different data provided by the different sensors in order to predict by statistical means the device failure occurrence and consequently anticipate the power device replacement. Currently, for device ageing studies in a laboratory, electrical measurements of device parameters are often used as an indicator of device ageing. Furthermore, smart metal-oxide semi-conductor technology integrates more and more sensors that permit to measure quantities such as on-state resistance or junction temperature of the device. In power vertical diffused metal oxide semiconductor (VDMOS) assemblies, it would be interesting to make use of the VDMOS electrical parameters deviations in order to monitor the ageing state of the power assembly. To that end, we carry-out in this paper a study mainly based upon electro-thermo-mechanical simulations in order to identify the power VDMOS electrical parameters that could be monitored in order to access to the mechanical state of the power assembly and therefore anticipate the assembly failure. The power VDMOS R_on as well as zero temperature coefficient (ZTC) point are of interest because they are sensitive to mechanical stress. Consequently, in this paper, a procedure to minimise temperature impact on the Ron of the VDMOS transistor such that one could use the Ron as mechanical state indicator is shown. Another solution that makes use of a specific operating point of VDMOS (ZTC) which is temperature independent is also studied by simulations and experiment.