Microstructural Investigation of YBa₂Cu₃O_7-δ Films Deposited by Laser Ablation from BaF₂/Y₂O₃/CuO Targets

Abstract

Soon after the discovery of the high temperature superconductor YBa₂Cu₃O_7-δ, it was realized that thin films of this compound could have significant technological applications. Within several months, many research groups had succeeded in fabricating good quality films by evaporation, sputtering, and laser ablation.¹ This last process holds much hope for commercial application and has received a great deal of attention. The first samples were ablated from a bulk YBa₂Cu₃O_7-δ target, and post-deposition annealing in oxygen at 900°C was used to produce the superconducting phase. The best films fabricated by this method exhibited good superconducting transitions with zero-resistance temperatures (T_c0) in the range of 80–88 K, but they consistently had low critical current densities (J_c).² These results were only achieved through accurate control of all aspects of the laser deposition process. The film composition, in particular, is strongly dependent on the uniformity and energy density of the laser beam. Heating the substrate to high temperatures (over 650°C) during the deposition has resulted in much improved values for both T_c0 and J_c, but the inherent sensitivity to the deposition parameters is still the overriding consideration.^3–5