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High Temperature Superconductor Thin Films and Josephson Junctions

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Final rept. Sep 88-Aug 91,

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We have developed processes for the sputter deposition and device fabrication of Josephson tunneling structures made from YBCO materials. Very high critical current density YBCO films were used to make several different types of weak link structures. An 8-nm-diam focused ion beam was used to pattern thin YBCO films by implant damage. Procedures to fabricate trilayer devices utilizing a-axis films and non-superconducting YBCO barriers were developed. Superconducting transport through the barrier was observed, but was limited by base-electrode critical current density. These results indicated to us that edge-junctions would be better suited to the relatively low resistance barriers than are trilayer junctions. In the final stages of the program, we developed procedures for fabricating all YBCO edge junctions. Using a post annelaed base electrode and in situ counter electrode and no deposited barrier, we measured junction current densities up to 1,000,000 asqcm, demonstrating successful implementation of the steps required to make edge junctions, including successful annealing of the ion milling damage at the edge during counter electrode growth. This result indicates that barriers are not formed as uncontrolled artifacts of edge-junction processing, and is a crucial test of the feasibility of fabricating edge junctions with reproducible, controlled properties using deposited barriers. Edge-junction devices were fabricated with a 10-nm non-superconducting YBCO barrier under the superconducting counter- electrode layer. In these devices, the junction critical current was controlled by the barrier material. We observed significant suppression of the critical current by RF radiation, an indication of the successful demonstration of an all-YBCO tunneling device.

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  • Electricity and Magnetism

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