Microstructural characterization of YBaCuO thin films deposited by rf magnetron sputtering as a function of annealing co
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John P. Allen CVC Products Inc., Rochester, New York 14603-1886 (Received 26 April 1990; accepted 11 October 1990)
Thin films of YiBa2Cu3O7-;t have been prepared on MgO, SrTiO3/Al2O3, and A12O3 substrates by rf magnetron sputtering. A buffer layer of SrTiO3 was deposited on A12O3 by flash evaporation. The as-deposited films on MgO and SrTiO3/Al2O3 had a (00/) orientation whereas the films on A12O3 were randomly oriented. The lattice parameters along the c-axis for the as-deposited films on MgO and SrTiO3/Al2O3 were longer than the value for bulk crystals and decreased by annealing in oxygen. The critical temperatures (Tc) of the superconducting transitions increased with gradual shortening of the c lattice parameter. These changes in Tc's and c's were attributed to the reduction in the concentration of crystal defects formed during sputter deposition. A detailed x-ray diffraction study of YBaCuO on MgO and SrTiO3/Al2O3 was carried out and values for the particle sizes and nonuniform strain were obtained by using an integral breadth method. It was observed that changes in Tc were related to the reduction in nonuniform strain. The presence of preferred orientation and grain growth after annealing was also studied. The highest Tc's tended to occur when the (00/) texture was strongest. I. INTRODUCTION
Recent progress in high temperature superconductors has led to the possibility for technological applications of superconducting thin films. Practical methods for making good quality films are essential. Various deposition techniques such as sputtering, electron beam co-evaporation, molecular beam epitaxy, laser beam evaporation, and flash evaporation, among others, have been used. Sputtering, using a single oxide target, has been the most widely used method to prepare YBaCuO thin films. In earlier work, post-annealing at high temperatures was required after deposition to obtain superconducting films. This heat treatment often causes a severe interface reaction between the substrate and film. Post-annealing is also undesirable in fabricating superconducting films associated with semiconductor devices. In the present work a reactive ion sputtering technique at a substrate temperature of 650 °C in an oxygen partial pressure was used. This method permitted forming superconducting films in situ in the vacuum system. In addition to reactive ion sputtering, use of buffer layers has been successful in preventing substrate-film interaction at the interface in the preparation of superconducting films in situ. However, high temperature annealing may still be necessary to improve the crystallinity and superconducting properties of the films. In this study, YBaCuO thin films were prepared by rf magnetron sputtering from a single target in the pres252 http://journals.cambridge.org
J. Mater. Res., Vol. 6, No. 2, Feb 1991 Downloaded: 16 Mar 2015
ence of an oxygen and argon gas mixture. An extensive x-ray diffraction microstructural study was then carried out to understand the relationships between the structural imperfections and th
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