The Effect of Operating Conditions on the Radiation Resistance of VDMOS Power FETs

The effect of gamma radiation on the threshold voltage, "On" resistance, and breakdown voltage of VDMOS Field Effect Transistors operating under various bias conditions is presented. The drain-source breakdown voltage and the "On" resistance of these devices have been found to be unaffected by irradiating the devices to a total dose of 4×104 rads. The electrical parameter affected by irradiation is the gate threshold voltage. The threshold voltage shift at a particular radiation level for devices biased with both gate and drain voltage has been determined to be dependent only on the magnitude of the gate voltage during irradiation. This shift has been found to be independent of the drain-source voltage (30-80 volt range) and operating frequency (10-50kHz range). Practically no annealing occurs at room temperature. However, these devices have been found to recover to within 10% of their initial threshold voltage after annealing at 200°C under gate bias of 18 volts for 22 hours.