An Improved Small-Signal Equivalent Circuit for GaN High-Electron Mobility Transistors

Abstract

We found that the extrinsic inductance shows a strong bias dependence in GaN high-electron mobility transistors (HEMTs) based on a conventional small-signal equivalent circuit, with a decreasing value as current increases. This abnormal behavior not only complicates the parameter extraction, but also indicates potential invalidity of formulations for the extrinsic inductance, leading to a parameter value of less physical meaning. By introducing a novel intrinsic resistance along with an inductance in the equivalent circuit, the bias dependence of extrinsic elements can be inhibited, and a high precision fit between simulation and measurement can be achieved for GaN HEMTs with a gate length of $0.1~\mu \text{m}$ up to 65 GHz.