Low frequency noise in thin gate oxide MOSFETs

Abstract

Low frequency, 1/ f, noise of the drain current, I D, fluctuations was measured on a series of Si MOSFETs with the gate oxide thickness, t ox, varied from 25 to 40 Å by steps of 5 Å. The salient point of this work is a demonstration that, at sufficiently low I D intensities, a mean low noise level in the MOSFETs is reduced as the gate oxide becomes thinner. This is explained assuming that the noise originates from the electron capture/release on Si/SiO 2 interface/border traps. The flat band voltage fluctuations, observable as noise, are linked then to the oxide charge fluctuations by a factor, that is inversely proportional to the gate capacitance, C ox, and thus proportional to t ox. At higher I D, the results are more complicated, as the access resistance noise is also involved. We provide an interpretation of the ensemble of the data and show that the noise analysis can furnish quantitative estimates of several device characteristics. Device degradation and its consequences for the low frequency noise at higher current levels are also discussed.