Effect of neutron irradiation on the breakdown voltage of power MOSFET´s

The effect of neutron irradiation on power metaloxide-semiconductor field effect transistor (power MOSFET) breakdown voltage has been investigated. Transistors with various breakdown voltage ratings were irradiated in a TRIGA nuclear reactor with cumulative fluence levels up to 5/spl times/10/sup 14/ neutrons/cm/sup 2/ (1 MeV equivalent). Noticeable increases in the breakdown voltages are observed in n-type MOSFET´s after 10/sup 12/ neutrons/cm/sup 2/ and in p-type MOSFETs after 10/sup 12/ neutrons/cm/sup 2/. An increase in breakdown voltage of as much as 30% is observed after 5/spl times/10/sup 14/ neutrons/cm/sup 2/. The increase in breakdown voltage is attributed to the neutron-irradiation-induced defects which decrease the mean free path and trap majority carriers in the space charge region. The effect of positive trapped oxide charge due to concomitant gamma radiation and the effect of the termination structure on the increase in breakdown voltage are considered. An empirical model is presented to predict the value of the breakdown voltage as a function of neutron fluence.<>