LNL Annual Report 2004

In this paper we brefly describe an experimental study of the role of the parasitic transistor on the charge generation phenomenon observed during the impact of heavy ions on medium voltage power MOSFET [1-5]. We observed that new generation power MOSFETs reveal, during single event impact, a premature damage of the gate structure before a typical burnout occurrence. The damage is related to the activation of the parasitic BJT but hasn’t to be interpreted as a damage of the drain structure. The damage is detected by an increase of the gate leakage current, but can’t be confused as a typical gate rupture event. Although the gate leakage current seems to recover its original value, the damage is irreversible and leads the gate oxide to the breakdown when the device is subsequently biased. The experimental procedure showed that in this damage mechanism the activation of the parasitic BJT plays a relevant role, so the generated charge and the device robustness could be influenced by the epilayer parameters.