Fabrication of High T C Superconducting Composite Structure
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FABRICATION OF HIGH Tc SUPERCONDUCTING COMPOSITE STRUCTURE
J.Chang, L.W.Song, R.Barone, P.Bush, F.Yang, S.Patel, Y.H.Kao, and D.T.Shaw New York State Institute on Superconductivity, State University of New York at Buffalo, Bonner Hall, Buffalo, New York 14260 ABSTRACT The laser ablation technique was used to fabricate high Tc superconducting composite structures. The multilayered structures were fabricated in-situ by changing the target during deposition. Thin MgO films and yttrium-stabilized ZrO2 films were used as buffer layers. The composite films were successfully fabricated on ZrO2(100) substrates. There is negligible interdiffusion occurring at the interfaces and the Jc at 77K is higher than 10 5 A/cm2 for YBCO films in a triple layered structure. INTRODUCTION Single layered YBa2Cu306.8 (YBCO) films with high Tc and Jc have been obtained using various deposition techniques. (1),(2),(3),(4),(5) However, to study the pinning effect in the films, mechanical properties for power applications, and junction construction for device applications, it is necessary to fabricate and to understand multilayered structures using superconducting films. In this paper, we use the laser ablation technique to fabricate the composite structures. By using in-situ deposition with about 600oc substrate temperature, the multilayers were successfully fabricated on ZrO2(100) substrates. Negligible interdiffusion occurs at the interfaces between YBCO films and thin buffer layers. At 77K, YBCO films in a three layered structure have Jc's higher than 105 A/cm2 . RESULTS
AND DISCUSSION
In our experiments, superconducting YBCO films and buffer layers were prepared by laser ablation technique on Zr02(100) single crystal substrates. MgO and yttriumstabilized Zr02 (YSZ) were used as buffer layers. We fabricated the multilayered structure by changing the target during deposition. An excimer ArF laser with 193nm wavelength was used. The target-to-substrate distance was 70mm. The target was rotated during ablation and the laser beam incident angle was 450 to the normal of the target. The heater block was heated to 550o-650oc during deposition and an oxygen jet was placed close to the substrate. The oxygen pressure was monitored at the bottom of the chamber. The operating pressure was 20-35mtorr.
Mat. Res. Soc. Symp. Proc. Vol. 169. @1990Materials Research Society
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Figure 1 shows a typical result of Tc measurement of a 0.4um thickness YBCO film. The Tc is 90K and Jc=10 6 A/cm2 at 77K. Films with good superconducting properties can be obtained with thicknesses up to 0.6um. These films show preferential orientation with the c-axis normal to the substrate. The lattice constant of the c-axis is estimated to be about 11.70A. Figure 2 shows an Auger electron depth profile of the YSZ/YBCO film. The thickness of the YSZ and YBCO layers are 350A and 2000A, respectively. The elements of YBCO are not detected on the surface of the film. This indicates that the YSZ buffer layer is completely continuous. The MgO buffer layers show similar results. F
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