On the limits of noise performance of field effect transistors

A reduction in gate length L
_g
of FETs below 100 nm and corresponding improvements in transconductance gm, cutoff frequency ft and maximum frequency of oscillation fmax has not resulted in expected improvements in measured minimum noise temperatures Tmin (or noise figures F
_min
). This observation applies to all FET technologies currently in use: FETs, HEMTs and MOSFETs. An explanation of this observation is offered by treating drain noise as a suppressed shot noise with current spectral density given by F2qI
_d
Δf, where F is a suppression factor. The re-analysis of the available experimental data for GaAs FETs, HEMTs, InP HEMTS and MOSFETs demonstrates that the suppression factor F can be as small as 0.1 for long gates but increases rapidly for gate lengths shorter than 100 nm. It is consistent with the expectation that for Lg→0 the drain noise should approach pure shot noise and F→1.