Langevin forces and generalized transfer fields for noise modeling in deepsubmicron devices

We show that the standard impedance field method that considers as noise so urce the spectral density of velocity fluctuations is not appropriate for t he calculation of noise spectra in deep submicron devices where spatial cor relations between velocity fluctuations cannot be neglected. To overcome th is drawback, we develop a new scheme in which the noise sources are given b y the instantaneous accelerations of relevant dynamic variables caused by s cattering events. Accordingly, generalized transfer fields describing the p ropagation of fluctuations to the device terminals are introduced. By using this scheme, we show that, in contrast with the standard impedance field m ethod, noise modeling in submicron structures can be performed with no majo r difficulty and the dual representation of voltage and current noise is re covered.