MICROSTRUCTURES AND REPRODUCIBILITY FOR SEVERAL HIGH-TC JOSEPHSON-JUNCTIONS

We overview relationship between microstructures and reproducibility f or several types of Josephson junctions which we have studied by trans mission electron microscopy (TEM). For grain boundary type junctions, we found that although the orientation between two grains can be contr olled, the detailed orientation of grain boundary is uncontrollable. T herefore, the critical current varies dramatically even prepared under the same conditions. When one of the grain boundaries is a basal-plan e-facet (001) grain boundary, the grain boundary structure is always t he same such that a good control of critical current becomes available . In the case of multilayer junctions, a growth of a-axis multilayer b y homoepitaxy is proposed to challenge SIS junction, because recent re sults show that the substrate smoothness can be obtained less than 10 Angstrom within 5 mu m area.