TID effects occur in MOS-gated transistors in radiation environments where proton and gamma-rays irradiate the devices. TID effects seriously affect the electrical characteristics of Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET). They can eventually result in the malfunction of power systems when exposed to long-term radiation conditions. We irradiated gamma-rays and protons into 1.2 kV SiC MOSFETs and evaluated the change in electrical properties to analyze the TID’s effects. As a result of the experiment, the threshold voltage (V_T) and on-resistance (R_on) of 1.2 kV SiC MOSFETs decreased because positive fixed charges inside the oxide increased depending on the radiation dose of the gamma-ray and fluence of the proton irradiations. The degradation of breakdown voltage (BV) occurred owing to a change in the depletion curvature at the edge of termination regions owing to the trapping of the charge in the field’s oxide.

The 1.2 kV SiC MOSFET with a buried oxide was verified to be effective in improving switching characteristics. It is crucial to reduce the gate–drain charge (Q_GD) of devices to minimize switching loss (E_total). The SiC MOSFET with a split gate and device with a buffered oxide have been proposed by previous studies to reduce the Q_GD of the devices. However, both devices have a common issue of the concentration of the electric field at the gate oxide. In this paper, we propose the 1.2 kV SiC MOSFET with a buried oxide to reduce the Q_GD and suppress the electric field crowding effect at the gate oxide. We analyzed the specific on-resistance (R_on,sp), Q_GD and the maximum electric field at the gate oxide in the off state (E_ox,max) according to the width (W_BO) and thickness of the buried oxides (T_BO). The device with the buried oxide, under optimal conditions, showed lower E_ox,max and E_total without significant increase in R_on,sp in comparison to the device with a conventional structure. These results indicate that the buried oxide can improve the switching characteristics of 1.2 kV SiC MOSFETs.

1.2 kV silicon carbide (SiC) MOSFETs with buffered oxide, which have been developed to reduce the gate–drain charge (Q _GD), have the problem that the electric field is crowded at the corners of the buffered oxide. In this paper, 1.2 kV SiC MOSFETs with tapered buffer oxide are proposed to suppress the electric field crowding effect. The devices with tapered buffer oxide having an angle of 40° demonstrate a maximum electric field at the gate oxide in the off-state (E _ox,max) of 1.87 MV·cm⁻¹, achieving a 13.4% reduction compared to devices with a conventional structure. Additionally, it is verified that the output characteristics of 1.2 kV SiC MOSFETs can be improved by applying tapered buffer oxide. This is because the junction FET region can be designed with high concentration through the suppression of the electric field of the tapered buffer oxide.

We investigated the effects of gate bias regarding the degradation of electrical characteristics during gamma irradiation. Moreover, we observed the punch through failure of 1.2 kV rated commercial Silicon Carbide (SiC) Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) due to the influence of gate bias. In addition, the threshold voltage (V_T) and on-resistance (R_on) of the SiC MOSFETs decreased significantly by the influence of gate bias during gamma irradiation. We extracted the concentration of carriers and fixed charge (Q_F) in oxide using N-type SiC MOS capacitors and Transmission Line Measurement (TLM) patterns to analyze the effects of gamma irradiation. The Total Ionizing Dose (TID) effect caused by high-energy gamma-ray irradiation resulted in an increase in the concentration of holes and Q_F in both SiC and oxide. To analyze the phenomenon for increment of hole concentration in the device under gate bias, we extracted the subthreshold swing of SiC MOSFETs and verified the origin of TID effects accelerated by the gate bias. The Q_F and doping concentration of p-well values extracted from the experiments were used in TCAD simulations (version 2022.03) of the planar SiC MOSFET. As a result of analyzing the energy band diagram at the channel region of 1.2 kV SiC MOSFETs, it was verified that punch-through can occur in 1.2 kV SiC MOSFETs when the gate bias is applied, as the TID effect is accelerated by the gate bias.