Microwave characterization and modeling of packaged HEMTs by a direct extraction procedure down to 30 K

The Knowledge of the small-signal equivalent circuit of microwave GaAs field effect transistors (FETs) is crucial for the design of low-noise amplifiers and is very useful to support the analysis of the transistor performance. This paper reports the results of our experimental activity concerning the application of an improved procedure for the direct extraction of the model element values from scattering (S-) parameter measurements. This analytical procedure was tested on low-noise pseudomorphic high electron mobility transistors (pHEMTs) up to 6 GHz and at cryogenic temperatures without any optimization or tuning adjustment. This paper reports the behavior of the intrinsic elements versus bias condition; the experimental results were found to match the theoretical expectations. The very good agreement between the simulated and measured S-parameters confirms the validity of the proposed method. To carry out the experimental activity, a properly designed cryogenic setup operating in our laboratory, which allows performing direct current (de) and microwave characterization down to 30 K, was employed.