Low frequency noise in AC biased metallic tunnel junctions

We study the effect of an AC bias on the low frequency noise, notably $1/f^\gamma$ with $\gamma<2$, of metal-insulator-metal tunnel junctions at room temperature. The measurement is performed in the 6Hz-100kHz frequency range with an AC excitation above 1MHz. We observe that $1/f^\gamma$ noise is dominant across our measurements though the shape of the spectra varies. The effect of the DC excitation seems to be very different on the noise generated by the junction than that of the AC excitation, thus questioning the fact that the observed noise is due to resistance fluctuations that the bias only reveals.