Improved Fabrication Process for Monolithic Integrated High-T_c dc Superconducting Quantum Interference Devices

We have developed a new fabrication process for monolithic integrated high-T-c dc superconducting quantum interference devices (SQUIDs) that enables us to prevent a degradation of the junction T-c. In the new process, bicrystal junctions are fabricated simultaneously with a flux transformer by using the top superconducting layer. The junctions in YBa2Cu3O7-x-based SQUIDs fabricated by this process exhibited a T-c of approximately 85 K, indicating no significant degradation. In contrast, conventional monolithic SQUIDs where junctions are fabricated by using the base superconducting layer showed a junction T-c typically below 65 K. A fabricated monolithic dc SQUID magnetometer with a 500 mu m square washer, a 23-turn 5-mu m-wide input coil, and a pickup loop 6 x 7 mm(2) in outer dimension showed an effective area of 1.2 mm(2) and an IcRn Of 180 mu V at 77 K.