Takuma Matsuda

Radiation response of silicon carbide metal–oxide–semiconductor transistors in high dose region

Radiation response of vertical structure hexagonal (4H) silicon carbide (SiC) power metal–oxide–semiconductor field effect transistors (MOSFETs) was investigated up to 5.8 MGy. The drain current–gate voltage curves for the MOSFETs shifted from positive to negative voltages due to irradiation. However, the drain current–gate voltage curve shifts for the MOSFETs irradiated at 150 °C was smaller than those irradiated at room temperature. Thus, the shift of threshold voltage due to irradiation was suppressed by irradiation at 150 °C. No significant change or slight decrease in subthreshold voltage swing for the MOSFETs irradiated at 150 °C was observed. The value of channel mobility increased due to irradiation, and the increase was enhanced by irradiation at 150 °C comparing to irradiation at RT.

Change in Characteristics of SiC MOSFETs by Gamma-Ray Irradiation at High Temperature

Radiation response of 4H-SiC vertical power Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) was investigated at 150°C up to 10.4 MGy. Until irradiation at 1.2 MGy, the drain current – gate voltage curves of the SiC MOSFETs shifted to the negative voltage side, and the leakage of drain current at gate voltages below threshold voltage increased with increasing absorbed dose. However, no significant change in the electrical characteristics of SiC MOSFETs was observed at doses above 1.2 MGy. For blocking characteristics, there were no degradations of the SiC MOSFETs irradiated at 150°C even after irradiated at 10.4 MGy.

Gamma-ray irradiation response of the motor-driver circuit with SiC MOSFETs

Gamma-ray irradiation effects of motor-driver circuit composed of SiC MOSFETs under motor driving with different PWM frequencies were investigated. The driving current and voltage waveforms were normal when the irradiation exceeded 1.1 MGy at PWM frequency of 10 kHz. In addition, the motor was still rotating in this total dose. We compared the irradiation responses of SiC MOSFETs between the cases of driving states and no bias. The drain current – gate voltage characteristics with no bias shifted to the negative voltage side wider than the driving states. Also the leakage current in the case of driving state is fewer than that of no bias.

Improvement of radiation response of SiC MOSFETs under high temperature and humidity conditions

The response of hexagonal (4H) silicon carbide (SiC) power metal–oxide–semiconductor field effect transistors (MOSFETs) to gamma-ray irradiation was investigated under elevated temperature and humid conditions. The shift in drain current–gate voltage (I D–V G) curves towards negative voltages and the leakage of I D with a current hump due to elevated temperature irradiation were suppressed under high humidity conditions relative to dry conditions. This result can be explained in terms of the reduction in trapped oxide charge and oxide–SiC interface traps generated by irradiation due to the humid conditions. In addition, during irradiation at elevated temperature in humid conditions, electron traps at the oxide–SiC interface obviously decrease at doses above 100 kGy.