Fabrication and characterization of Y-Ba-Cu-O and Nd-Ba-Cu-O ramp-edge junctions with an interface-modified barrier

The fabrication process for YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) ramp-edge junctions with an interface-modified barrier has been studied. The conditions of electron cyclotron resonance (ECR) ion etching and following annealing treatment were optimized by evaluating the mean roughness of the ramp surface using atomic force microscope (AFM) observation. We could obtain resistively-shunted junction (RSJ) type current-voltage characteristics for the junctions with the counterelectrode YBCO layer deposited at temperatures lower than 720/spl deg/C, while a deposition temperature higher than 755/spl deg/C resulted in a high-J/sub c/ superconducting contact. The junctions exhibited an I/sub c/R/sub n/ product of 1.0-1.9 mV and magnetic field modulation of I/sub c/ more than 90% at 4.2 K. By applying the optimum etching condition to a NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (NBCO) base electrode and employing a slightly higher annealing and deposition temperature, YBCO/NBCO ramp-edge Josephson junctions with a similar I/sub c/R/sub n/ product were successfully obtained.