Trap assisted tunneling as a mechanism of degradation and noise in 2-5 nm oxides

The mechanism of stress induced leakage current and dielectric breakdown is examined through 1/f noise in the tunneling current of 1.7-5 nm oxides. Before breakdown occurs, we find a linear relationship between low frequency 1/f noise and the increased current due to stress. This behavior can be described by a model of trap assisted tunneling for both phenomena. We develop a quantitative new model for the noise in terms of fluctuations in a trap assisted tunneling current through the oxide and show that the traditional charge-state fluctuation model is inconsistent with the voltage scaling of the noise. Our results demonstrate that noise can be used as a very sensitive measure of interface states, with a higher sensitivity than conventional capacitance-voltage relations. We show that the conduction mechanism in stressed and unstressed oxides is fundamentally different with the tunneling current in the unstressed oxides dominated by the fundamental limit of direct tunneling. Finally, noise in the post-breakdown state is used to understand the softening of breakdown at lower stressing conditions.