A YBCO multilayer process using surface-modified junction technology

We have developed processes for fabricating a YBa₂Cu₃O_7-x-multilayered structure which contains surface-modified junctions and a ground plane. A process of Ar-and-oxygen-ion milling, which was developed for fabricating the ramp-edges of the junctions, was applied to planarization of the structure´s insulating layers. A process of milling with 500-V O₂ ions, which was developed for cleaning the ramp-edge surfaces, was applied to improve the critical current values for via-contacts in the structure. The fabricated junctions exhibited an average I_cR_n product of 0.7 mV and a 1σ-spread in the critical current of about 10% at 30 K. The sheet inductance of the strip-lines in the structure was less than 1.0 pH per square in the range below 60 K. The obtained values for I_cR_n product, 1σ-spread, and sheet inductance allow us to realize the high-speed operation of single-flux-quantum circuits at temperatures from 20 to 40 K.