Suppression of Dispersive Effects in AlGaN/GaN High-Electron-Mobility Transistors Using Bilayer SiNx Grown by Low Pressure Chemical Vapor Deposition

A bilayer SiN
_x
passivation scheme has been developed using low pressure chemical vapor deposition (LPCVD), which effectively suppresses the dispersive effects in AlGaN/GaN high-electron-mobility transistors (HEMTs) for microwave power operation. The bilayer LPCVD passivation is compared with in-situ SiN
_x
passivations by metal-organic chemical vapor deposition (MOCVD) and ex-situ SiN
_x
passivations by plasma-enhanced chemical vapor deposition (PECVD). The HEMTs were fabricated and characterized in terms of pulsed IV, transient drain current, and load pull. The devices passivated with in-situ MOCVD SiN
_x
or PECVD SiN
_x
exhibit significant current slump (~ 40% and knee-voltage walkout, while the bilayer LPCVD SiN
_x
passivated device shows negligible current slump (~6% and knee-voltage walkout. These characteristics are directly reflected in the large signal operation, where HEMTs with bilayer LPCVD SiN
_x
have the lowest dynamic ON-state resistance and highest output power (5.4 W/mm at 3 GHz).