Reliability assessment on power MOSFETs working in energy absorption mode

The on state resistance of power MOSFETs tasked to perform repetitive avalanche operations is subject to modifications caused by the growth of voids and cracks in the source metallization. Endurance tests are the traditional way to monitor these changes in order to assess the device reliability. However, they are very time expensive, requiring even months of uninterrupted operations. An interesting alternative consists in the assessment of the reliability through a suitable model, but no standard techniques have been developed up to now to accomplish this task. A possible approach is followed in this paper exploiting a dynamic analysis of the temperature distribution over the source metal. Coupling the thermodynamic analysis with a reliability model, carried out from the Coffin-Manson law, the device degradation over the time can be estimated and the level of reliability as well. The consistence of the obtained reliability prediction is confirmed by comparison with results of endurance tests. The described approach can be usefully applied to assess the reliability of MOSFETs in a large set of applications in the automotive field.