Study on low temperature processing for rare-earth-free high Tc superconducting thin films* K. Setsune, Y. Ichikawa, T. Kamada, K. Hirochi, H. Adachi, S. Kohiki, and K. Wasa Central Research Laboratories, Matsushita Electric Industrial Co., Ltd., Moriguchi, Osaka 570, Japan Thin flms of rare-earth-free high T~ superconductors such as Bi-Sr-Ca-Cu-O and TI-Ba- Ca-Cu-O systems have been prepared by RF-magnetron sputtering and subsequent annealing. These thin films showed a polycrystalline structure and had highly orientated c-axes perpendicular to the substrates. These thin films exhibited superconducting transitions above 100 K and critical current densities of more than 105 A cm -2 at 77 K, which was the same order of magnitude as the polycrystalline Ln-Ba-Cu-O thin films. This paper reports details of this fabrication process using XPS data, and discusses the possibility of low temperature preparation for rare-earth-free high Tc superconductors. Keywords: high Tc superconductivity; low temperature studies; thin films Since thc first report by Bednorz and Muller, a wide variety of perovskite-type oxide superconducting mater- ials having high critical temperatures (To) has been discovered ~ -'~. Much effort has gone into the preparation of thin films of these materials 5- i0. Historically, thin films of perovskite-type oxides were studied as basic research on ferroelectric materials. Thin films of BaTiO 3 and PbTiO 3 were attempted, and their ferroelectricities were evaluated 't. Recently, perov- skite thin films such as PZT (PbTiO3-PbZrO3) and PLZT ((Pb, La)(Zr, Ti)Oa) have been studied in relation to the synthesis of thin film dielectrics, pyroelctrics, piezeolectrics, electro-optic materials, and acousto-optic materials 12. Thin films of BPB (BaPbO3-BaBiO3) were studied as oxide superconductors 13. Thin films of rare-earth high T~ superconductors of La~ _xSr, CuO~ and YBaaCu3Ov_y have now been syn- thesized successfully due to previous studies on ferro- electric thin films of perovskite-type oxides 5 -8. Recently, new bulk compounds of high Tc Bi-Sr-Ca-Cu-O and TI-Ba-Ca-Cu-O systems have been prepared 3"a. Many experiments have been made to fabricate thin films of the new rare-earth-free superconductors 9'1°. These experi- ments suggest that c-axis orientated thin films can be successfully depositied on crystalline substrates. The Bi-Sr-Ca-Cu-O films with T~ = 80 K and T1-Ba-Ca-Cu-O films with T~ = 100 K have crystal structures that cor- respond to those of the low T~ phase ceramics 14't5. A single high T~ phase has been prepared for Bi-Sr-Ca-Cu-O *Paper presented at the International Conference on Critical Currents in High-Temperature Superconductors, Snowmass Village, Colorado, USA, 16 19 August 1988 0011-2275/89/030296-08 $03.00 ,~:)1989 8utterworth & Co (Publishers) Ltd 296 Cryogenics 1989 Vol 29 March supplement thin films, but thin films with a high T c single phase are difficult to prepare. The crystal structures and super- conducting properties of such films are not well under- stood. Thin film processes for high Tc superconductors of perovskite-type oxides are classified into four methods: I deposition at a low substrate temperature followed by post-annealing at around 900°C; 2 deposition at a crystallizing temperature of 600 800°C, followed by post-annealing; 3 deposition at the crystallizing temperature under an oxidizing atmosphere; 4 deposition at lower than crystallizing temperature under an active or energetic atmosphere. It has been confirmed that the superconducting thin films of Gd-Ba-Cu-O were successfully grown at 600°C by sputtering deposition using method 4 ~6. The onset temperature was 95 K with zero resistance temperature Tc = 86 K. Post-annealing causes interdiffusion between the substrate and the film, which degrades the super- conductivity of the thin films. Moreover, low temperature processing without high post-annealing is required for the application of these new high "/-~. superconducting thin films. Basic processes for perovskite thin films Thin films of amorphous phase are deposited at the substratc temperaturc (T~) below the crystallizing tem- perature (Tc~). The T~r for perovskite-type oxides is