Small Signal Modelling of 100 nm GaAs pHEMT Process in the 4 K to 293 K Temperature Range

HEMT-based Low Noise Amplifiers (LNAs) are often used as the primary sensing device in microwave/ millimeter-wave receiver systems. In noise critical applications, such as radio astronomy, to improve their noise performance, they are cooled to cryogenic temperatures of 20 K and lower. At room temperature, the small signal equivalent circuit (SSEC) of HEMT transistors is well-known and supports LNA design. At low temperatures, however, the circuit model is less representative due to temperature related effects that alter the device current-voltage response. In order to improve the understanding of cryogenic HEMT performance, the SSEC parameters of a commercial 100nm gate length GaAs pHEMT have been extracted across a range of temperatures extending from 4 K to 293 K. The results indicate an unexpectedly complex temperature dependent behavior with variation in the SSEC parameters occurring as the transistor is cooled below 150 K and 15 K. The experimental data and extracted SSEC parameters will support future LNA designs across a range of low temperature operating conditions and help to guide the selection of parameters such as the optimum temperature for operation. In addition, the SSEC can also provide key insights into the operation of HEMT transistors at low temperatures.