Operation of 4H-SiC high voltage normally-OFF V-JFET in radiation hard conditions: Simulations and experiment

Operation of high-voltage 4H-SiC vertical-JFET in radiation hard environment was investigated by simulation and experiment. Commercial 1700 V normally-OFF SiC JFETs in TO-247 package were irradiated with fast neutrons to fluences of 4.0 × 1014 cm− 2 (1 MeV Si equivalent) and the effect of radiation on their characteristics was then thoroughly analyzed. Four degradation mechanisms were identified, of which the most important is the increase of JFETs ON-state resistance due to the mobility degradation and removal of carriers from transistor's light doped channel and drift regions. As a result, the JFET ON-state losses grow and, at fluences higher than 4 × 1014 cm− 2, the low doped n-regions are fully compensated and transistor loses its functionality. On the contrary, irradiation slightly improves JFET's switching characteristics. The effect of neutron irradiation on operation of SiC V-JFET in a real application was then investigated on the step-UP 15 V/60 V DC-DC converter where the SiC JFET was used as an active switch. Converter characteristics were analyzed by means of the mixed-mode simulation using the developed 2D model of the neutron irradiated transistor. Results showed that the duty cycle of the PWM regulator is growing due to the increase in the voltage drop on the switching JFET. This effect, which is caused by the abovementioned increase the JFET's ON-state resistance, increases power dissipation and deteriorates converter efficiency. Finally, the effect of neutron irradiation on operation SiC V-JFET in the 850 V/24 V auxiliary flyback switching mode power supply was analyzed. We showed that the growth of the ON-state resistance increases transistor's conduction losses and decreases converter efficiency. Exceeding the fluence of 3.3 × 1014 cm− 2 neutrons then causes JFET overheating and subsequent destruction.