As-Grown Superconductivity of Bi-System Thin Films Prepared by Magnetron Sputtering with Three Pb Doped Targets: (Bi 1.6
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AS-GROWN SUPERCONDUCTIVITY OF Bi-SYSTEM THIN FILMS PREPARED BY MAGNETRON SPUTTERING WITH THREE Pb DOPED TARGETS: (Bil.6 Pb 0 .4 ) 1 + a (SrCa) 2 Cu3 0, (Bi 1.6 Pbo.4) 1 (SrCa) 2 + c Cu3 0x and (Bi 1 .6 Pbo. 4 ) 1 (SrCa) 2 Cu3 +c 0, (a= 0.S, b= 1,c= 1.5) KEN'ICHI KURODA, MASAMI TANIOKU, KAZUYOSHI KOJIMA, and KOICHI HAMANAKA Central Research Laboratory, Mitsubishi Electric Corporation Tsukaguchi, Amagasaki, Hyogo 661, JAPAN
ABSTRACT Superconducting Bi system thin films have been formed on MgO(100) substrates by RF magnetron sputtering from three Pb-doped targets: Bi 2 .4Pb0 .6 Sr 2 Ca 2 Cu 3 O0,,Bi 1.6 Pb0 .4 Sr3 Ca 3 Cu 3 0 , and Bil. 6 Pbo. 4 Sr 2 Ca2 Cu 4.5 0 ,. The as-grown films formed at substrate temperatures above 600 °C showed superconductivity, though, they did not contain Pb. The film, formed at 660°C and kept at the same substrate temperature and gas pressure as the sputtering conditions for 5 h after deposition, showed a resistivity drop at 115 K and zero resistivity at 83 K. The Jc value of the film was 4x10 5 A/cm 2 at 77 K and 3x10 ' A/cm2 at 20 K. INTRODUCTION It is well known that BiSrCaCuO superconductors[I] have at least three superconducting phases: T c of 110 K with a c-axis constant of 37 A (a high- Tc phase), Tc of 80 K with a c-axis constant of 31 A (a low-Tc phase) and Tc lower than 20 K with a c-axis constant of 24 A. To utilize these superconductors for microelectronic applications, it is necessary to synthesize them in the form of thin film at low temperature. Nevertheless, in most cases, superconducting BiSrCaCuO thin films were formed by subsequent annealing at rather high temperature. There are a few reports,[2-8] up to date, that have obtained as-grown superconductivity of Bi system thin films. Moreover, in these reports, Tc values of the films were rather low compared with those of bulk samples or annealed films.[9-10] In previous papers,[11,12] we also reported the results of superconducting properties for as-grown BiSrCaCuO thin films. The films had onset temperature above 100 K, however, zero resistivity temperature was 75 K. The main reason why a zero resistivity temperature as high as that of bulk samples cannot be obtained lies in the difficulty in forming a pure high-Tc phase in the as-grown state. As is well knownJ13,141 the addition of Pb enhances the formation of the high-Tc phase. Thus, we tried forming as- grown Bi system thin films using Pb-doped targets. Furthermore, we carried out in situ annealing process to improve the superconductivity of the as- grown films, since it has been reported[5,61 that Tc of the film with the low-Tc phase increases by annealing at low temperature. EXPERIMENTAL The Bi(Pb) SrCaCuO thin films were grown on MgO (100) substrates by RF magnetron sputtering from three targets: Bi 2.4 Pb0 .6 Sr2 Ca 2 Cu 3 0 ., Bil. 6 Pb0 .4 Sr 3 Ca 3 Cu 3 0 x and Bi 1.6 Pbo.4 Sr 2 Ca 2 Cu 4 .5 0 .. Each target had a 50 % excess of Bi+Pb, SrCa and Cu compared with the composition of the high-Tc phase (2223) , and also a Pb/Bi value of 0.2. As described in our
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