EFFECT OF NEUTRON-IRRADIATION ON THE BREAKDOWN VOLTAGE OF POWER MOSFETS

The effect of neutron irradiation on power metal-oxide-semiconductor f ield effect transistor (power MOSFET) breakdown voltage has been inves tigated. Transistors with various breakdown voltage ratings were irrad iated in a TRIGA nuclear reactor with cumulative fluence levels up to 5 X 10(14) neutrons / cm(2) (1 MeV equivalent). Noticeable increases i n the breakdown voltages are observed in p-type MOSFET's after 10(13) neutrons / cm(2) and in p-type MOSFETs after 10(12) neutrons / cm(2). An increase in breakdown voltage of as much as 30% is observed after 5 X 10(14) neutrons / cm(2). The increase in breakdown voltage is attri buted to the neutron-irradiation-induced defects which decrease the me an free path and trap majority carriers in the space charge region. Th e effect of positive trapped oxide charge due to concomitant gamma rad iation and the effect of the termination structure on the increase in breakdown voltage are considered. An empirical model is presented to p redict the value of the breakdown voltage as a function of neutron flu ence.