Analysis of the gate voltage fluctuations in ultra-thin gate oxides after soft breakdown

The time-dependence of the gate voltage [V/sub G/(t)] during constant current stress of MOS capacitors with a 2.4 nm gate oxide layer after the occurrence of soft breakdown is analysed. It is shown that the fluctuations observed in VG(t) are nonGaussian and can be fitted by Levy distributions. The long-range correlations in VG(t) are investigated by using the Detrended Fluctuation Analysis (DFA). From this analysis, it is found that long-range antipersistent correlations exist in the gate voltage signal. These can be qualitatively explained by a dynamic percolation model, taking into account the trapping-detrapping of electrons within the percolation cluster formed after the occurrence of soft breakdown.