Thermal annealing of MgO substrate increases 1/f noise in YBaCuOx at 300Â K and reduces the sheet resistance in the superconducting thin film

In this work, we characterize YBaCuO high Tc superconducting thin films deposited on (0 0 1) MgO substrates and compare their noise properties. The films were sputtered under the same conditions on substrates that were annealed at different temperatures prior to deposition. The noise measurements were performed at 300 K. The films exhibit 1/f noise due to the conductivity fluctuations and the results are compared with Hooge's empirical relation. The normalized noise spectral density (Sv/V2), measured at 300 K as a function of the substrate annealing temperature Ta, displays a bell-shaped dependence with a maximum at an anneal temperature Ta = 1050 °C. Two models based on the empirical relation are proposed to explain the observed results: a slight reduction in sample resistance goes hand in hand with a strong increase in 1/f noise after annealing of the substrate.