Thin film processing for high- T c superconductors of the Bi-system
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Thin film processing for high-Tc superconductors of the Bi-system Kiyotaka Wasa, Hideaki Adachi, Kumiko Hirochi, Yo Ichikawa, Tomoaki Matsushima, and Kentaro Setsune Central Research Laboratories, Matsushita Electric Ind. Co. Ltd., Moriguchi, Osaka 570, Japan (Received 21 September 1990; accepted 4 March 1991)
Basic thin film deposition processes for controlled deposition of the high-Tc superconductors of the Bi-systems are described. The layered structures of Bi-oxide superconductors are fabricated by a multitarget sputtering process. The multitarget sputtering process realizes the controlled deposition of single phase Bi-oxide superconductors, Bi2O2 • 2SrO • (n — l)CaO • nCuO 2 for n = 1 to 5. The minimum thickness controlled by the multitarget sputtering is a half crystal unit-cell of around 15 A, and the superlattices comprising (AkBk) • m, where A and B denote the Bi-oxide superconductors with different numbers of C u - 0 layers, could be fabricated for k > 1, although ion mixing takes place during the sputtering deposition due to the bombardment of the highly energetic sputtered adatoms. Multitarget sputtering will be available for the fabrication of the artificially-made layered oxide superconductors (ALOS). I. INTRODUCTION
Rare-earth-free high-Tc superconductors of Bi-SrCa-Cu-0 (Bi-system) and Tl-Ba-Ca-Cu-0 (Tlsystem) show the layered perovskite structure comprising two-dimensional arrays of C u - 0 pyramids or octahedra with apical oxygen which are formed by the C u - 0 layers. The superconducting transition temperature and/or the superconducting phase will be governed by the number of the C u - 0 layers, as indicated in Table I.1"11 Thin films of the Bi- and Tl-systems are prepared by physical and/or chemical deposition processes similar to the deposition of the rare-earth highTc superconductors of La-Sr-Cu-0 (LSC-system) and Y-Ba-Cu-O (YBC-system). Their superconducting phases are essentially controlled by the number of the Cu-0 layers during the film growth. This paper describes the basic thin film processing for the Bi-system and discusses the possibility of the deposition of the artificially made layered oxide superconductors (ALOS) by the sputtering process.
II. BASIC THIN FILM PROCESSING Thin film processing for the rare-earth high-Tc superconductors, LSC and YBC systems, is classified into three processes: process (1), deposition at a low substrate temperature followed by postannealing at around 900 °C; process (2), deposition at a crystallizing temperature of 600 to 800 °C followed by postannealing; process (3), deposition at the crystallizing temperature under an oxidizing atmosphere.12 The basic thin film processing for the rare-earthfree high-Tc superconductors of the Bi- and Tl-systems is essentially the same as that of the rare-earth high-Tc superconductors. J. Mater. Res., Vol. 6, No. 7, Jul 1991
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Several deposition processes are proposed for the deposition of the high-Tc superconductors of the Bisystem, including cathodic sputtering
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