Investigation of the threshold voltage shift of SiC MOSFETs during power cycling tests

Inhalt:
Power cycling (P/C) tests are performed to trigger package related failures under accelerated conditions. In case of silicon carbide (SiC) MOSFETs however, a shift of the threshold voltage Vth – which is caused by carrier trapping within the chip and thus not related to package fatigue – may cause an undesired shift of the operating point, of device characteristics used to determine virtual junction temperature Tvj, and even the usual failure criteria might be met because of it. In this paper the influence of Vth shift is investigated to allow separating the effects. For this purpose, a power cycling test bench has been equipped with a measurement facility for DeltaVth during each power cycle. Commercial discrete SiC power MOSFETs serve as exemplary devices under test.