Fabrication and characteristics of 0.12 µm AlGaAs/InGaAs/GaAs pseudomorphic HEMT using a silicon nitride assisted process

Abstract

We report the fabrication of a 0.12 µm T-gate with a silicon nitride assisted process. A two-step etch process was performed to define the gate footprint in the SiNx. The SiNx was etched either by dry etching (RIE) alone or by using a combination of wet and dry etching. The gate recessing was done in two steps including a wet etching for the removal of the damaged surface layer and a dry etching for the narrow recess. We have seen that the increases of the cut-off frequency fT and the maximum oscillation frequency fmax are 39% and 16%, respectively. This was believed to be due to a remarkable decrease of the gate-source and gate-drain capacitances by 25% and 18.3%, respectively. The improvement in RF performance can be understood in terms of the decrease in parasitic capacitances due to SiNx and the gate recess etching method.