YBa2Cu3O7-δ Superconducting Films Prepared by Low Pressure Post-annealing

YBa2Cu3O7-delta precursor films are deposited on 2 '' LaAlO3 wafer by the co-evaporation technique using Y, BaF2 and Cu as evaporation sources. After deposition, the films are annealed at low-pressure atmosphere with the composition of oxygen and water vapour. Compared with the normal pressure annealing, it is shown that low pressure can greatly improve the superconducting properties of 2 '' YBCO films with thickness larger than 500 nm, as the microcrack on films surface becomes unobservable the microwave surface resistance is greatly reduced. Furthermore, it is also revealed that the optimal processing window for making high quality superconducting YBCO films through ex-situ process is relatively small, therefore the ambient in annealing furnace is crucial important and should be precisely controlled.