Technology-Independent Analysis of the Double Current-Gain Peak in Millimeter-Wave FETs

This letter is aimed at discovering and analyzing anomalous phenomena affecting millimeter-wave FETs, focusing on a GaN HEMT as a case study. For the first time, we show that the real parts of the impedance parameters can increase and then decrease with frequency, due to the resonance of the extrinsic reactive elements. This resonance may be detected as a peak in the magnitude of the short-circuit current-gain. Such a peak is found to be substantially bias and temperature insensitive and to manifest at frequencies higher than the other current-gain peak (CGP), due to the resonance between intrinsic capacitances and extrinsic inductances, giving origin to the double CGP.