RF Investigations on HEMT's at Cryogenic Temperatures Down to 20 K using an On-Wafer Microwave Measurement Setup

Microwave measurements at cryogenic temperatures are very important to investigate the pronounced microwave performance of High Electron Mobility Transistors (HEMT) /1,2/. In order to perform an exact small signal analysis the On-Wafer measurement technique is an indispensable tool. An On-Wafer measurement setup to determine the s-parameters of these devices at temperatures down to 77 K was presented by Laskar et al. /3,4/. However, for the combination of HEMT devices and high Tc superconductors investigations at lower temperatures have to be carried out. For this reason a microwave On-Wafer measurement setup at temperatures from 300 K down to 20 K has been developed. Both, s-parameter and noise measurements, can be performed in the frequency range from 45 MHz to 40 GHz and 2 GHz to 18 GHz, respectively. Using this equipment measurements on pseudomorphic and AlGaAs/GaAs FET will be presented.