Comparison of YBCO thin films and SQUIDs prepared by ion beam deposition and RF and DC unbalanced magnetron sputtering

Results obtained with DC SQUIDs prepared by ion beam deposited films of YBa₂Cu₃O_x on substrates of (100) yttria stabilized zirconia (YSZ) have been previously reported. Superconducting films have subsequently been deposited by DC and RF unbalanced magnetron sputtering on various substrates including oriented and unoriented YSZ and lithium niobate. Details of films prepared by a different method are presented. Also reported are preliminary results on polycrystalline DC SQUIDs and an attempt to relate the SQUID properties with the morphology and film structure in each case. The implications of off-stoichiometry on film properties are discussed. It is shown that there is little difference between ion beam, RF, and DC unbalanced magnetron sputtering for the production of superconducting YBCO films providing the film is stoichiometric to better than 5%. Films with barium deficiencies over 7% are insulating. The advantage of one deposition method over the other is that RF unbalanced magnetron sputtering does not deplete the target of barium as rapidly as the other techniques. Targets can last up to three times longer