Reliability of Repetitively Avalanched Wire-Bonded Low-Voltage Discrete Power Trench n-MOSFETs

摘要

This paper, for the first time, investigates the reliability of wire-bonded low-voltage discrete power trench n-MOSFETs that have been subjected to repetitive unclamped inductive switching (RUIS). Automotive MOSFETs driving inductive loads may be subjected to RUIS; hence, there is a need to characterize the failure mechanisms in such applications. The failure mechanisms of repetitively avalanched wire-bonded MOSFETs are shown to be wire-bond lift-off and source metal degradation/fatigue due to thermomechanical stress cycling. Temperature excursions from avalanche pulses cause thermomechanical stresses on the wire-bond/source-metal interface as a result of differences in thermal expansion coefficients between silicon and aluminum. Trench MOSFETs exhibited an average of 10% increase in on-state resistance due to source metal fatigue after 100 million cycles of repetitive avalanche. The number of cycles to failure is investigated as a function of the avalanched induced temperature changes and is shown to follow the Coffin–Manson law. These results are important for designers of automotive systems since they are capable of predicting the long-term reliability of wire-bonded discrete power semiconductor components.