On the dependence of FET noise model parameters on ambient temperature

A generally accepted noise model of a FET without gate leakage current requires the knowledge of the elements of an equivalent circuit and three temperatures: physical temperature Ta and equivalent temperatures, Tg of intrinsic gate resistance and Td of drain conductance. Experimental confirmations have been published for III-V FETs and HEMTs and also for MOSFETs. There is, however, still a disagreement whether Tg and Td are merely fitting parameters or possess physical meaning. It is generally accepted that Tg ≈ Ta and Td ∝ Id/mm, but the dependence of Td on physical temperature Ta has not been established. This paper provides evidence that for a wide range of cryogenic temperatures the drain noise is independent of physical temperature Ta, and therefore is not “thermal”, and also confirms that the gate noise represented by Tg is of purely thermal origin, and therefore may not be “induced” by the drain noise.