Gate Oxide Reliability in Silicon Carbide Planar and Trench Metal-Oxide-Semiconductor Field-Effect Transistors Under Positive and Negative Electric Field Stress

This work investigates the gate oxide reliability of commercial 1.2 kV silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) with planar and trench gate structures. The performance of threshold voltage (Vth) and gate leakage current (Igss) in SiC MOSFETs is evaluated under positive and negative gate voltage stress. The oxide lifetimes of SiC planar and trench MOSFETs at 150 °C are measured using constant voltage Time-Dependent Dielectric Breakdown (TDDB) testing. From the test results, it is found that electron trapping and hole trapping in SiO2 caused by oxide electric field (Eox) stress affect the Vth of SiC MOSFETs. The saturation and turnaround behavior of the Vth shift during positive and negative gate voltage stresses indicates that the influence of charge trapping in the gate oxide varies with stress time. The Igss under positive and negative gate voltages depends on the tunneling barrier height for electrons and holes, respectively, which can be calculated using the Fowler–Nordheim (FN) tunneling mechanism. Moreover, the presence of near-interface traps (NITs) affects the barrier height for holes under negative gate voltages. The behavior of Vth shift and Igss under high-temperature gate bias reflects the charge trapping occurring in different regions of the gate oxide. In addition, compared to SiC planar MOSFETs, SiC trench MOSFETs with thicker gate oxide tend to exhibit higher lifetimes in TDDB tests.