Stress Analysis and Lifetime Estimation on Power MOSFETs for Automotive ABS Systems

Stress analysis and lifetime estimation are required in order to guarantee higher and higher levels of reliability of automotive power electronic devices. Stress analysis is oriented to investigate the effects of all the possible physical cause of failures, according to the defined device mission. On the basis of the stress analysis, and of a suitable reliability model a life time prediction can be performed. This is useful to predict the suitability of the device under evaluation to the prescribed mission, as well as to improve the design of new generations of devices. An experimental technique is exploited in this paper to evaluate the stress exerted on planar power MOSFETs designed to equip automotive ABS systems. The technique is based on an accurate experimental analysis of electro-thermal cycles, exploiting a laboratory tool tailored around an infrared microscope. It enables an high resolution dynamic temperature mapping with a large bandwidth. Such a tool makes also possible the evaluation of the effects of charge trapping phenomena occurring on Power MOSFETS as result of unavoidable gate overvoltages. According to a reliability model based on the Coffin Manson law, finally it is shown that gate voltage spikes can dramatically reduce the expected life time.