SUPERCONDUCTING PROPERTIES OF NB0.75ZR0.25-OXIDE-NB0.75ZR0.25 TUNNELJUNCTIONS

We have fabricated symmetrical Nb0.75Zr0.25/Oxide/Nb0.75Zr0.25 tunnel junctions having cross type geometry. The superconducting films constituting the electrodes of the junctions were obtained by RF magnetron sputtering, and the tunnel barrier was grown by natural oxidization in air. From the current-voltage characteristics of the junctions, we have measured the temperature dependence of the energy gap of Nb0.75Zr0.25 and compared this dependence with BCS-theory results. The magnetic-field diffraction pattern of the Josephson current of the junctions allows us to evaluate the penetration depth of the superconducting films. We also estimate the surface impedance of the NbZr film by measuring the quality factor of the junctions. We discuss the results within the framework of the realization of superconducting tunnel devices and coatings for superconducting accelerating cavities.