The main objectives of this work concerns the on-wafer high frequency noise measurements of low noise transistors (GaAs and InP HEMTs) at cryogenic temperature. We propose a new approach to de-embed the measured noise figure or noise power by taking into account the temperature distribution of the whole bench. For measurements at 77K, the gradient of temperature between the DUT and the receiver or the noise source is greater than 200K and the temperature distribution along the probes and cables is non uniform. This temperature distribution has to be accurately known to de-embed the measured noise figure and especially for low noise device like lattice-matched or metamorphic HEMTs.
The temperature distribution along the probes and cables is obtained using a 3-D thermal modeling (ANSYS) and has been checked through thermal sensors measurements. The inputs of the thermal simulations are the material composition and associated thermal properties of the probes, connectors and cables. This temperature distribution associated to a RLCG transmission line are afterwards implemented in CAD tool (ADS). In order to check the validity of such model, we have measured the noise power of a 50 Ω resistance for different temperatures (77 K to 295 K). At 77 K, after a de-embedding procedure using the distributed temperature model, we obtain an equivalent noise temperature of the resistance of 77 K ± 10 K. This de-embedding method will be applied to extract the noise parameters of cooled down HEMTs.