Reliability of Medium Blocking Voltage Power VDMOSFET in Radiation Environment

An experimental study of the effect of the epi-layer parameters on the heavy ion impact reliability of a medium voltage power MOSFET is presented for the first time. The tested devices has been constructed by using the typical gate structure of 200V VDMOSFET and different epi-regions. The analysis has been performed on a statistical base and allows us to correlate the charge generated, the ion energy and the bias voltages. The information extracted proves a failure mechanism, involving the damage of the gate oxide, quite insensitive to the charge generated (ion energy) and strongly dependent on the epi-layer doping. It is then shown that the new generation of medium blocking voltage power MOSFETs, during radiation exposure, is less subject to the avalanche mechanisms or to the activation of the parasitic bipolar transistor and shows a failure event involving the gate structure initiated by the development of a large electric field that propagates up to the surface of the gate oxide causing its degradation.