High Performance AlGaN/GaN Metal–Insulator–Semiconductor High Electron Mobility Transistors Fabricated Using SiN/SiO2/SiN Triple-Layer Insulators

Abstract

We proposed and fabricated AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) using SiN/SiO2/SiN triple-layer insulators. The role of each insulator is as follows: The topmost SiN film mechanically supports the T-shaped gate, the middle SiO2 film, which is damaged during the dry etching of the topmost SiN film, can be wet-chemically etched, and the bottom SiN film stabilizes the AlGaN surface. Therefore, the proposed MIS-HEMTs are mechanically stable in the sub-50-nm-gate region and free from damage caused by dry etching. We obtained a cutoff frequency fT of 139 GHz for a 45-nm-gate MIS-HEMT. This fT is the highest value for AlGaN/GaN HEMTs grown by metal organic chemical vapor deposition. We also estimated the average electron velocity under the gate to be 2.4×107 cm/s for a 120-nm-gate MIS-HEMT by transit time analysis.