For the purpose of fabricating all-high-Tc superconducting tunnel junctions, nickel oxide (NiO
x) and the heterostructure (NiO
x/Bi
2Sr
2CaCu
2O
x and Bi
2Sr
2CaCu
2Ox/NiOx/Bi
2Sr
2CaCu
2O
x) were investigated. Bi
2Sr
2CaCu
2O
x (BSCCO) films were deposited as a base electrode on a MgO or SrTiO
3 substrate using a dc hollow cathode sputtering system.
In situ superconducting BSCCO films deposited in Ar +20%O
2 gas at Ts =700°C on a MgO substrate were of the c-axisoriented 2212 phase.
A NiO
x layer was formed by reactive sputtering in Ar +20%O
2 gas using a Ni hollow cathode, and the layer on the BSCCO film had (100) orientation. The BSCCO films on the NiO
x layer deposited at Ts = 700°C showed superconductivity and were c-axis-oriented. XPS depth analysis was performed on BSCCO/NiO
x/BSCCO heterostructures, and interdiffusion was not observed. From the analysis of XPS spectra, the nickel oxide layer was found to mainly consist of NiO, but a small amount of Ni was also detected. However, Ni can be oxidized by annealing in oxygen atmosphere.
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