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 T-a and equivalent temperatures, T-g of intrinsic gate resistance and T-d 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 T-g and T-d are merely fitting parameters or possess physical meaning. It is generally accepted that T-g approximate to T-a and T (d) proportional to Id/mm, but the dependence of T-d on physical temperature T-a has not been established. This paper provides evidence that for a wide range of cryogenic temperatures the drain noise is independent of physical temperature T-a, and therefore is not "thermal", and also confirms that the gate noise represented by T-g is of purely thermal origin, and therefore may not be "induced" by the drain noise.