Improved interface reliability in AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors using Al2O3/ZrO2 bilayer

Abstract

AlGaN/GaN high-electron-mobility transistors (HEMTs) have emerged as key components for high-frequency and high-power applications. In particular, metal–insulator–semiconductor (MIS) HEMTs are gaining attention as a promising solution for improving reliability and reducing gate leakage. Owing to its excellent interface quality with GaN and AlGaN surfaces, Al2O3 has been extensively employed as a gate insulator in MIS-HEMTs, resulting in a low interface trap density. Nevertheless, its relatively low dielectric constant compared to high-k materials such as ZrO2 or HfO2 can limit gate control. Oxygen vacancy-related traps in Al2O3 also lead to lateral leakage and dynamic Ron degradation. To overcome these limitations, we investigate a bilayer gate insulator composed of Al2O3/ZrO2. Using energy-dispersive X-ray spectroscopy, frequency-dependent parallel conductance analysis, high-resolution transmission electron microscopy, and dynamic Ron measurements, we confirmed enhanced interface stability and a reduction in oxygen vacancy-induced bulk traps. The Al2O3/ZrO2 bilayer MIS-HEMT exhibited improved electrical performance, including a lower subthreshold swing (68.1 mV/dec), higher saturation current (172.7 mA/mm), and a stable dynamic Ron/static Ron ratio below 1.1 under quiescent drain bias conditions up to 40 V. In contrast, the Al2O3 single-layer device showed a notable increase in Ron, with ratios exceeding 1.3. These findings demonstrate that the Al2O3/ZrO2 bilayer gate insulator effectively suppresses trap-induced degradation, leading to enhanced performance and reliability in GaN-based MIS-HEMTs.