Thermally hardened AlGaN/GaN MIS-HEMTs based on multilayer dielectrics and silicon nitride passivation

AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) were demonstrated to operate at temperatures of up to 600 °C. High-quality multilayer gate dielectrics (Al2O3/SiO2/SiON) were developed to enhance the thermal stability of the MIS-HEMTs at high temperatures. Furthermore, we found that silicon nitride passivation and circular structure can effectively reduce the off-state drain current, which is critical for high-temperature operations. Based on the optimized process, we demonstrated the AlGaN/GaN MIS-HEMTs with record high I o n / I off ratios (1011 at room temperature and 105 at 600 °C) and high transconductances (47 mS/mm at room temperature and 8 mS/mm at 600 °C for a channel length of 2.4 μm). The maximum transconductance was enhanced by ∼28% after the operation at 600 °C. Lifetime measurement of the MIS-HEMT showed stable DC characteristics with a nearly unchanged on-state drain current and threshold voltage over the course of 25-h thermal stress at 525 °C.