Charge-Based Formulation of Thermal Noise in Short-Channel MOS Transistors

In this communication we develop a charge-based formulation for the thermal noise in short-channel transistors. We arrive at a closed expression for the channel thermal noise including the velocity saturation effect for all the operating regions of the MOSFET. Such a result is increasingly important not only in strong inversion but also in moderate and weak inversion owing to technology scaling into the deep submicron regime. We based the calculation of the thermal noise on the impedance field method [4], which allows calculating the effect of local fluctuations on the measurable noise at the device terminals. Our derivation follows the same procedure used in [2], but rather than constraining the result to strong inversion, our quite general result is expressed in terms of the inversion charge densities at the source and drain terminals.