Modified 1/f trapping noise theory and experiments in MOS transistors biased from weak to strong inversion—Influence of interface states

Low-frequency 1/f noise in Si n-channel MOSFET's is measured from weak to strong inversion, through the relative spectral density of the drain current fluctuations
S_{I}_{D}/I^{2}_{D}
. Under specific conditions, a plateau is observed in the variations of
S_{I}_{D}/I^{2}_{D}
versus the gate voltage in weak inversion followed by a steep decrease in strong inversion. A modified trapping noise theory based on the McWhorter's assumptions and valid in all the working regimes is developed to account for this behavior. Excellent agreement is obtained with the variations of several parameters: gate and drain biases, geometry, oxide and depletion capacitance, temperature, and technologies. The influence of fast interface states is particularly studied and is related to the noise variations and the oxide trap densities.