S-parameter characterization of GaAs gate SISFETs at liquid nitrogen temperatures

SISFETs were characterized at both room and liquid nitrogen (LN) temperatures to evaluate their dynamic performance. Equivalent circuit parameters obtained from low-frequency parametric measurements were compared to those deduced from S-parameter measurements. The measurements were made on a bifurcated gate structure consisting of two identical gate fingers totaling 70 μm in width. Microwave characterization of the devices relied on measurement of the S-parameters over a 50-MHz-26-GHz range using an HP8510B network analyzer and cascade probes. The room- and LN-temperature characterization of SISFETs shows no evidence of anomalous behavior. The equivalent circuit parameters deduced from microwave measurements are consistent with those derived from the low-frequency measurements. The low gate leakage, improved gm, and unchanged gate capacitance result in a high fT at LN temperatures, indicating potential for enhanced performance in digital systems.