Thermal stability and small-signal characteristics of AlGaN/GaN HEMTs with gate insertion metal layer for millimeter-wave applications

Abstract

The effect that insertion gate metals have on GaN millimeter-wave devices undergoing a postmetallization annealing (PMA) process was investigated. It was found that the PMA process increases the gate resistance (R-g), which is responsible for a decrease in the maximum oscillation frequency (f(max)). The resistance was examined as a function of line patterns containing various gate metal stacks, including Ni/Au and Ni/Mo/Au, before and after annealing from a low temperature to 550 degrees C. The metal stack with an Mo insertion layer effectively suppressed Au diffusion into GaN and reduced the increase in the gate metal resistance. For the fabricated AlGaN/GaN-on-Si high-electron-mobility transistors with a Ni/Mo/Au gate, stable gate reliability, improved current collapse characteristics, and small-signal characteristics were also achieved compared to those of the Ni/Au gate. (C) 2017 American Vacuum Society.