Preparation of Yba 2 Cu 3 O 7 - X . Superconducting Thin Films by Means of Single Target Rf-Sputtering+
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PREPARATION OF YBa 2Cu307-x SUPERCONDUCTING THIN FILMS BY MEANS OF SINGLE TARGET RF-SPUTTERING HERMAN D.L. WEYTEN**, R. DE BATIST***, P. NAGELS*** and J. CORNELIS* *S.C.K./C.E.N., Materials Development Dept., Boeretang 200, B-2400 Mol, Belgium **University of Antwerp (UIA), Dept. of Chemistry, Universiteitsplein 1, B-2610 Wilrijk, Belgium ***University of Antwerp (RUCA), Middelheimlaon 1, B-2020 Antwerp, Belgium
ABSTRACT High Tc superconducting thin films have been deposited on sapphire by means of RF-sputtering from a single stoichiometric target of YBa 2Cu3 07x composition. The YBa Cu30 films were deposited in an argon-oxygen 7 atmosphere on a substrate 1wich reached a temperature of a 400*C during deposition. The study of stoichiometry and homogeneity of the as-deposited films, by means of electromicroprobe analysis (ENPA), was used to optimize the sputtering parameters of the system. To achieve superconductivity, with an onset of = 90 K, a high-temperature, post-deposition thermal treatment in oxygen was necessary. Resistivity measurements show that, with respect to the bulk samples, zero resistivity is lowered as a result of substrate interaction. The use of buffer layers can improve the quality of the superconducting thin films.
INTRODUCTION Since the discovery of superconducting ceramics [1,2] with high critical temperatures many research groups have been stimulated to explore its technological potential. Because thin films will be an essential element for a number of possible electronic and sensor applications, considerable research effort has been spent on various techniques to deposit YBa 2Cu3O07x superconducting thin films on different substrates
[3-7]. In this paper we report on our contribution to the study of synthezising reproducible YBa Cu O superconducting thin films on sapphire substrates by means of sing e target RF-sputtering. It bill be shown that the study of the influence of the sputtering parameters is important to obtain stoichiometric thin films and that the use of buffer layers can improve the quality of the superconducting YBa 2 Cu3 0 7 -x films. DEPOSITION TECHNIQUE The target was prepared by the solid state reaction method, starting with the appropriate amounts of Y^0 3 , BaCO3 and CuO powders in the molar ratio 1:2:3. The preparation of the bulk material has been discussed in detail elsewhere [8]. The resulting powder was pressed into the shape of a disc (0 50 x 3 mm) and resinteied at 950=C for at least 24 h in air. After t a final heat treatment at 400 C for 2 h in vacuum, the target had a density of 82.2 % of the theoretical value and was examined by SEM/EDX and EMPA to confirm the composition which proved to be Ba/Y = 2.045 and Cu/Y = 3.104 (atomic ratio) (Fig. 1). However in the relatively low-density target some small areas of Cu-rich material could sometimes be found near the holes. From this target the superconducting thin films were then deposited by means of HF-sputtering. +Work carried out in the framework of the IUAP-1I Belgian Government grant. Mat. Res. Soc. Symp. Pro
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