Non-Gaussian behavior and anticorrelations in ultrathin gate oxides after soft breakdown

The time dependence of the gate voltage VG(t) after soft breakdown of metal-oxide-semiconductor capacitors with a 2.4 nm SiO2 layer has been measured. It is found that the VG(t) fluctuation distributions are non-Gaussian, but can be described by a Lévy stable distribution. The long-range correlations in VG(t) are investigated within the detrended fluctuation analysis. The Hurst exponent is found to be H=0.25±0.04 independent of the value of the stress current density J. It is argued that these are universal features of soft breakdown and are due to trapping–detrapping of electrons in and away from the primary percolation path.