QUALITY CONTROLS ON HIGH-TC BASED TUNNEL-JUNCTIONS

We report on systematic studies to perform quality controls on planar tunnel junctions realized on high-T(c) superconductors (HTS). Tunneling spectra of the orthorhombic 90K and 60K YBa2Cu3O7-delta phases, of the magnetically doped, tetragonal YBa2(Cu0.96Fe0.04)307 compound and of the Bi2Sr2CaCu2O8 system are analyzed. The traditional, low-bias barrier analysis as well as a number of tests useful to investigate the ''status'' of the HTS surface layer are carried out. Evidence is given that some anomalous tunneling data can be understood in terms of a Kondo-type scattering between tunneling electrons and magnetic impurities at the interface. The reproducibility of the tunneling spectra for different junction fabrication conditions is also discussed.