High-Tc YBa2Cu3O7 thin films produced by multilayer sputter deposition

Attractive applications for thin films with high superconducting transition temperatures include input coupling coils for SQUIDs as well as Josephson junctions and SQUIDs themselves. Such applications place many demands on the films, including reproducible composition, good electrical transport properties, uniformity over large substrate areas, short deposition turnaround times, high-quality film surfaces and interfaces, and film stability. Consequently, the authors are developing a multilayer deposition technology to fabricate thin films of YBa2Cu3O7. The films are produced by sequential sputtering from three metallic targets onto substrates attached to a rotating table controlled by a programmable stepping motor. Presently, all of the authors films require post-annealing outside the deposition system to form the high-Tc superconductor structure, although the eventual intention is to produce films by an entirely in-situ method. The multilayer technique is well-suited for obtaining reproducible film composition as the substrates remain over each target for a long enough time to average out the small fluctuations in the sputter deposition rate. The composition, post-annealing profile, and details of the layering are the primary factors determining the microstructure and transport properties of the films. Note that sputter deposition is intrinsically capable of producing layers of uniform thickness over substantial areas (> two inches in diameter for the authors' two-inch diameter targets at a target-to-substrate distance of 6.5 inches). The deposition system is also load-locked to decrease pumpdown time and to prevent deterioration of the targets, especially the Ba, thereby reducing the presputtering needed to clean the targets