Characteristics of YBa2Cu3O7-y Josephson junctions prepared with smooth ramp-edge surfaces

YBa2Cu3O7-y ramp-type Josephson junctions with PrBa2Cu3O7-y and SrTiO3 barriers have been fabricated on SrTiO4 (001) substrates. The surface morphology of the ramp-edge was examined using the atomic force microscope (AFM). The conditions of the photolithography process and the ion beam incident angle were optimized to improve the surface roughness at the ramp edge. Typically, smooth surfaces at the ramp-edge with a ramp angle of about 25 degrees and an average roughness of about 3 nm was achieved. Results indicate the junction properties are improved with a smooth ramp-edge surface. The details are discussed.