Interface-engineered Josephson-Kontakte

The Josephson junction is the key active device in the superconductor electronics. Junctions in the ramp-edge geometry provide the most flexible type, since the specific junction properties can be adjusted by the material and thickness of the barrier layer. Furthermore, they are compatible to a multilayer technology, enabling them for integrated-circuit applications. In this work, a new type of Josephson junction in the ramp-edge geometry made of the high-temperature superconductor YBa_2Cu_3O_7 (YBCO) was investigated. In the 'interface-engineered' junctions a natural barrier is formed by treatment of the ramp interface instead of depositing an artificial, non-superconducting barrier layer. The first part of the work describes the optimization of the several parts of the process and the investigation of the significant process parameters as well as their physical meaning. By application of statistical methods in the design and analysis of the experiments, potentially important factors and additionally their interactions could be examined thoroughly. A process was developed that yields Josephson junctions with reproducible properties which can be described by the 'resistively and capacitively shunted junction' (RCSJ) model. The critical current densities and the normal resistances of these junctions cannot be strongly influenced by the conduction of the process. However, a Lanthanum doping of the superconductor leads to a large variation of the parameters above a threshold La-concentration of about 5%. The investigation of the transport properties of the junctions forms the second part of this work. Measurements of the current-voltage characteristics with and without microvave irradiation and the behavior in a magnetic field demonstrate the RCSJ-similarity of the junctions as well as the homogeneity of the current transport through the barrier. (orig.)SIGLEAvailable from TIB Hannover: RA 831(3828) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman