The sputter deposition of cerium oxide thin films for superconducting electronics

Thin films of cerium oxide (CeO/sub 2/) have been deposited by r.f. reactive sputter deposition on yttria-stabilised zirconia (YSZ) and on YBCO thin films on lanthanum aluminate (LaAlO/sub 3/) substrates. Subsequent growth of YBa/sub 2/Cu/sub 3/O/sub (7-x/) (YBCO) by high pressure d.c. sputtering has yielded superconducting transition temperatures (T/sub c/s) of 89-91 K for unpatterned YBCO films. CeO/sub 2/ thin films have been patterned and subsequent YBCO growth has been examined. Oxygenation levels were monitored between growth and patterning stages by X-ray diffraction (XRD). A YBCO track has been fabricated crossing steps in a CeO/sub 2/ buffer layer. A critical current density (J/sub c/) of 0.8/spl times/10 /sup 10/Am/sup -2/ at 77 K as compared with 1/spl times/10 /sup 10/Am/sup -2/ for a flat YBCO track on flat CeO/sub 2/ was measured. Crossover test structures were made, having T/sub c/s of 89-91 K for top and 80-90 K for the bottom YBCO electrodes. A 400 nm thickness of CeO/sub 2/ was sufficient to insulate two superconducting layers and found to have a resistivity of 2/spl times/10/sup 7/ /spl Omega/m at 77 K.<
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