VDMOS Power Transistor Drain-Source Resistance Radiation Dependence
Data on the effects of neutron and gamma radiation on the drain-source resistance characteristics of power VDMOS transistors are presented. The change in resistance with neutron exposure is related to the resistivity of the drain material, which in turn can be related to the drain-source breakdown voltage. A device with a 450-V rating experienced a factor of 13 increase in resistance on exposure to a neutron fluence of 1014/cm2 whereas one with a breakdown voltage of 150 V experiences no increase in resistance. Threshold voltage shifts of about 2 V occurred at a gamma dose of 105 rad(Si) without bias and was accelerated by positive gate bias. All of these data are consistent with the predictions of a simple model for the dependence of drain-source resistance on gate voltage and drain resistivity. This model illustrates a general separability of neutron and gamma effects on power VDMOS devices. The systems implications for using this type device in a radiation environment are briefly addressed.