Langevin forces and generalized transfer fields for noise modeling in deep submicron devices

We show that the standard impedance field method that considers as noise source the spectral density of velocity fluctuations is not appropriate for the calculation of noise spectra in deep submicron devices where spatial correlations between velocity fluctuations cannot be neglected. To overcome this drawback, we develop a new scheme in which the noise sources are given by the instantaneous accelerations of relevant dynamic variables caused by scattering events. Accordingly, generalized transfer fields describing the propagation of fluctuations to the device terminals are introduced. By using this scheme, we show that, in contrast with the standard impedance field method, noise modeling in submicron structures can be performed with no major difficulty and the dual representation of voltage and current noise is recovered.