Tunneling barrier structure of Nb Pb and Nb (PbIn) thin film Josephson junctions studied by Auger electron spectroscopy and X-ray photoelectron spectroscopy analysis

The structure of the insulant barrier of Nb Pb and Nb (PbIn) thin film Josephson tunnel junctions is studied in detail by Auger electron spectroscopy and X-ray photoelectron spectroscopy analysis. The properties of these two types of junction are strictly related to the thin (2-3 nm) oxide acting as a barrier between the superconducting electrodes. Two oxides were found in each barrier: NbO and PbO in the Nb Pb junction and NbO and InO in the Nb (PbIn) junction. In addition, the present analysis shows a change with time of the PbO in contact with NbO: this result is correlated with junction aging. Finally, a comparison in terms of the stability of the two junctions is made: Nb (PbIn) devices seem to display a more stable behaviour with time. © 1982.