The Effect of Annealing Conditions on Magnetron Sputtered Superconducting Tl-Based Thin Films
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THE EFFECT OF ANNEALING CONDITIONS ON MAGNETRON SPUTTERED SUPERCONDUCTING Ti-BASED THIN FILMS
S.H. LIOU Behlen Laboratory of Physics and Center for Materials Research and Analysis, University of Nebraska-Lincoln, Lincoln, NE 68588-0111
ABSTRACT The annealing steps have been shown to be a crucial determinant of the quality of T1based superconducting films. In this study, we discuss the formation of the superconducting T12 Ba 2CaCu 20s and T12 Ba 2Ca 2 Cu 30 10 phases with varied post-annealing temperature and fixed annealing time. A x-ray, electron micro-probe, and scanning electron microscopy were carried out to evaluate the structure of superconducting phases formed for each annealing condition. For films deposited on SrTi0 3 substrates and heat-treated at 870 0 C for 15 min, the lower T, phase T12Ba 2 CaCu 2O8 becomes a major phase. The films consist of nearly pure T12Ba 2Ca 2 Cu 30 10 phase with T, (R=0) in the range of 100K to 118K and c-axis perpendicular to the film plane were obtained after annealing 880-890'C for 15 min. These films were epitaxy growth on SrTiO 3 substrates. INTRODUCTION There are many superconducting phases with T,'s above 100K in the TI-Ba-Ca-Cu-
0 system, in particular the T12Ba 2 Ca2 Cu 3 010 phase has demonstrated superconductivity up to 125K[1-4]. Interest in thin films is stimulated by the potential for applications. The annealing steps have been shown to be a crucial determinant of film quality[5-8]. In this study, we discuss the formation of the superconducting phase of TI-based films with systematically varied post-annealing temperature and fixed annealing time. Thin films of T12Ba 2CaCu 2O8 (2:2:1:2) and Tl 2Ba 2 Ca 2 Cu 3Oio(2:2:2:3) were routinely prepared on a wide variety of substrates (Y-ZrO 2, MgO, and SrTiO 3 etc.) The microstructure and crystal structure of the films depend very much on the heat treatment and the chemical composition. Results presented here will focus on films deposited on SrTiO 3 substrates. For films deposited on other substrates, the requirement of the heat treatment and chemical composition is slightly different with respect to the overall film quality and morphology. These results were discussed elsewhere[9]. FILM GROWTH Films were prepared by magnetron sputtering using a single composite oxide target. The sputtering target was made by sintering a mixture of T120 3 , BaO, CaO, and CuO powders with a ratio of 1:2:2:3. The sputtering gas was a mixture of Ar and 02 with a ratio about 1:1. The total pressure was maintained at 23 mtorr during the deposition. The substrate temperature was 200 0 C. The film thickness was 500 nm. To avoid the excessive decrease of TI during the heat treatment, the samples were wrapped in gold foil with pellets of compressed composite TI-Ba-Ca-Cu-O powders and sealed in a quartz tube. Mat. Res. Soc. Symp. Proc. Vol. 169. ©1990 Materials Research Society
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COMPOSITION, STRUCTURE AND MORPHOLOGY The film composition was determined by a Kevex electron-probe x-ray microanalysis. The composition of the as-deposited film was
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