Thin Film Deposition and Transport in 2223 Bi-Sr-Ca-Cu-O
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THIN FILM DEPOSITION AND TRANSPORT IN2223 Bi-Sr-Ca-Cu-O J.T. KUCERA, D.G. STEEL, D.W. FACE*, J.M. GRAYBEAL, T.P. ORLANDO, AND D.A. RUDMAN Center for Materials Science and Engineering, MIT, Cambridge, MA 02139. *Present address - Central R. &D., DuPont, Wilmington, DE 19898 ABSTRACT We have reproducibly prepared thin films of Bi-Sr-Ca-Cu-O with Tc >- 105K. Depositions were done at ambient temperature with a subsequent post-deposition anneal, and did not include lead substitution. X-ray diffraction data indicates a majority fraction of the 2223 phase. These films possess very large grains of the order of 20-30 gm in size. Post-deposition annealing conditions are a sensitive function of composition. Detailed transport measurements as a function of temperature and magnetic field have been obtained. EXPERIMENTAL PROCEDURE Thin films of amorphous Bi-Sr-Ca-Cu-Oxide were deposited onto ambient temperature, (100) oriented MgO substrates by RF triode magnetron sputtering from metallic Sr, Ca, and Cu-Bi targets, as described elsewhere[1-3]. The films were all approximately 200nm thick and had compositions of approximately Bi:Sr:Ca:Cu of 2:2:2:4.5 as measured by RBS. Following deposition, the films were annealed in a tube furnace in flowing argon-oxygen. The temperature was increased linearly from room temperature to the final annealing temperature in 30 minutes and furnace cooled over a period of about 2 hours. RESULTS Films with Tc(R=0) of 100K or higher have been produced in three different depositions and under four different annealing conditions establishing the reproducibility of the process. However, as can be seen in Table I, run-to-run composition variations of about 5% significantly affected the optimal annealing conditions. To date, we have been able to produce these high transition temperature films only in copper-rich samples, and then only by using long anneals on the order of 12 hours in low oxygen partial pressures. SEM studies (Figure 1) show the microstructure of these films changes dramatically with anneal temperature, with the highest Tc samples having large grains. Table I. Compositions and annealing conditions which produced Tc(R=0) of at least 100K. Composition Anneal Bi Sr Ca Cu 2.00 1.96 2.02 4.47 8700C for 12Hrs in 5%02 2.00 1.85 2.00 4.70 8800C for 12Hrs in 5%02 2.00 1.85 2.00 4.70 8700C for 30min in 100%02 + 8700C for 12Hrs in 5%02 2.00 1.71 1.95 4.59 8750C for 12Hrs in 10%02 Mat. Res. Soc. Symp. Proc. Vol. 169. ©1990 Materials Research Society
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Figure 1. SEM micrographs and theta two-theta x-ray scans of a set of films having composition Bi:Sr:Ca:Cu = 2.00:1.85:2.00:4.70 annealed in 5% 02, 95% Ar for 12 hours. As anneal temperature increases the grain size grows dramatically as does the relative vo
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