UBC Theses and Dissertations
Preparation and characterization of high temperature superconducting thin films Dew, Steven K.
Thin films of the Bi₂Sr₂Ca₂Cu₃O[sub y] superconductor with T[sub c] in excess of 106K were produced through a two step process involving rf magnetron sputtering of an oxide target followed by annealing in oxygen. The effects of various production parameters on the deposition and quality of the films were studied. During deposition, ion bombardment of the films directly in front of the sputtering target lead to an increase in film density and to resputtering. Films from this area tended to flake off of the substrate during processing. Heating the substrate during deposition reduced the flaking problem, but caused the concentration of bismuth to drop at temperatures above 350° C. Optimal post-deposition processing conditions were dependent on several factors including film composition, lead doping, and oxygen concentration in the annealing atmosphere. After processing, only lead doped films resulted in significant amounts of 2223 and zero resistance T[sub c]'s above 100K. The optimal initial film composition was Pb[sub 1.1]Bi₂Sr₂Ca₂Cu₃O[sub y]. The best annealing conditions for such films were 865-875°C for 16 h in flowing oxygen. During processing, films developed in a sequence of 2201, 2212, and, in lead doped films, 2223. The lead dopant was steadily lost during processing, and no detectable amounts remained in some of the best films after processing. Development of the 2223 phase stopped when the lead loss from the films was essentially complete.
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