BI-EPITAXIAL GRAIN-BOUNDARY JUNCTIONS IN YBA2CU3O7

We have developed a new way of making grain boundary junctions in YBa2Cu3O7 thin films by controlling the in-plane epitaxy of the deposited film using seed and buffer layers. We produce 45-degrees grain boundaries along photolithographically defined lines. The typical value of the critical current density of the junctions is 10(3)-10(4) A/cm2 at 4.2 K and 10(2)-10(3) A/cm2 at 77 K, while the rest of the film has a critical current density of 1-3 X 10(6) A/cm2 at 77 K. The current-voltage characteristics of the junctions show resistively shunted junction behavior and we have used them to fabricate dc superconducting quantum interference devices (SQUIDs) which show modulation at temperatures well above 77 K. This is the first planar high T(c) Josephson junction technology that appears readily extendable to high T(c) integrated circuits.