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

摘要

In this work, we have characterized YBaCuO high Tc superconducting thin films deposited on (001) MgO substrates and compared their noise properties. The films were sputtered on substrates which were annealed at different temperatures prior to deposition. The noise measurements were performed under the same conditions: 1) Without bias, the films are at equilibrium and exhibit only thermal noise proportional to the real part of the impedance for the voltage fluctuations or proportional to the real part of the admittance for the current fluctuations. 2) With bias, the films exhibit 1/f noise due to the conductivity fluctuations. The extra noise is compared with Hooge's empirical relation. The normalized noise spectral density (S_v / V~2) measured at 300 K as a function of the substrate annealing temperature displays a bell-shaped dependence with a maximum at a critical temperature.