INFLUENCE OF RAMP SHAPE AND MORPHOLOGY ON THE PROPERTIES OF YBA2CU3O7-DELTA-RAMP-TYPE JUNCTIONS

The correlation between the shape and the morphology of ramps prepared by ion-beam etching of YBa2Cu3O7-delta thin films, and the properties of ramp-type junctions were investigated in detail. We examined the i nfluence of different fabrication parameters on the YBa2Cu3O7-delta ra mps by atomic force microscopy. Ramp-type junctions were fabricated us ing PrBa2Cu2.9Ga0.1O7-delta as barrier material. We observed a strong influence of the shape of the ramp on the homogeneity and, thus, on th e transport properties of the junctions. Furthermore, we observed that the roughness of the ramps is strongly influenced by the voltage of t he ion-beam during etching. Best results are achieved when an addition al wet cleaning step by bromine solution in ethanol is introduced prio r to the deposition of the barrier and the top electrode. As a result from our optimization, the on-chip spread of the junction critical cur rent was reduced to 11%. (C) 1998 Elsevier Science B.V. All rights res erved.