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Ramp-type Josephson junctions with YBCO superconducting electrodes and PrBa2Cu2.6Ga0.4O6+δ(PBGCO) barriers were fabricated and characterized. The YBCO ramp junctions with 25 nm-thick barriers of PBGCO showed typical resistively- shunted-junction (RSJ)-like I-V behavior and 1σ spread of less than 13% in critical current density. Differential conductance-voltage characteristics registered using a lock-in technique indicate that the resonant tunneling via localized states in the barriers plays a dominant role in the conduction process of the ramp junctions.

Ramp-type Josephson junctions with barrier layers of Ga doped PrBa2Cu3O7-δhave been investigated using scanning and transmission electron microscopy. The microstructures have been correlated to the ramp geometry. The junctions exhibited low excess current. This is believed to be due to the uniform thickness of barrier layer deposited on the ion-milled edges. The uniformity of the barrier is presumed to be a result of the smooth ramp, which promoted uniform nucleation and epitaxial growth.