Influence of thermal annealing of MgO substrate on 1/f noise of YBaCuO superconducting thin films

In this work, we have characterized three NbNx thin films deposited on sapphire substrate and compared their noise properties. The three films were measured in the same conditions. In the first time, the films were characterized with an impedance analyzer from 20 Hz to 1 MHz. The films are then considered as a RC dipole with a resistor R in parallel with a capacitor C. With the Nyquist formula, we calculate the noise voltage spectral density SvTh of the RC dipole considering that only the resistor R exhibits thermal noise in unbiased samples. In the second time, noise measurements were made with the samples biased. Thanks to a four contacts configuration, we checked that contact noise do not contribute to our measurements. The difference between the measured noise and the calculated thermal noise SvTh shows an extra 1/f noise without GR noise contributions. The 1/f noise in the three films extra noise is compared. These results are also compared to the noise measured on NbN thin films deposited on silicon substrate [1]