Fabrication and performances of NbZr/oxide/NbZr thin film Josephson junctions

We report on the fabrication of symmetrical NbZr-Ox-NbZr Josephson junctions by means of thin film RF magnetron sputtering deposition. The insulating barrier consisted of natural oxide thermally grown in air at room temperature. The variation of the superconducting gap Δ as a function of the temperature was measured by recording the I-V characteristics. The experimental data are in good agreement with the dependence numerically computes from the BCS theory. The magnetic behavior of the maximum Josephson current was measured and both the magnetic penetration depth and the Josephson penetration depth were computed. By means of the Kulik theory on the junction self-induced resonances the microwave quality factor Q of the junctions, and the surface impedance of the films have been estimated. (orig.)