Reliability assessment of power MOSFETs working in avalanche mode based on a thermal strain direct measurement approach

A strong demand of even more compact and reliable power electronic devices has powered in the last years the development of advanced device design techniques. A key role in these techniques is played by the reliability assessment, a procedure that estimates the expected lifetime of power devices according to given mission profiles. The reliability assessment of a low voltage MOSFET working in avalanche mode is faced in this paper through a new experimental approach based on the Coffin Manson law and a direct measurement of the thermal strain over the Source Aluminum layer. The consistence of the proposed technique is evaluated by comparing obtained estimations of the progressive increment of the on state resistance with estimations carried out from other reliability models and endurance tests results. The described approach can be usefully applied to assess the reliability of MOSFETs in applications typical of the automotive field were power devices are tasked to operate in avalanche mode, such as: brake pump drivers, electromagnetic valve control, direct high-pressure injection, starter-alternator and active suspension systems.