Practical high T c Josephson junctions and dc SQUIDs operating above 85 K

Reproducible high Tc YBa2Cu3O7/Ag/YBa2Cu3O7 Josephson junctions have been fabricated using an entirely in situ step-edge technique. The junction process requires the deposition of a single high Tc film and the patterning is performed using standard photolithography and ion-beam etching. The junctions exhibit a well-defined supercurrent from 4.2 to 87 K and the ac Josephson effect is observed up to 80 K in response to microwave radiation. dc SQUIDs have been fabricated and show the expected periodic modulation of the critical current in a magnetic field at temperatures ranging from 4.2 to 85.7 K. All of the 56 devices fabricated and measured to date show a well-defined supercurrent from 4.2 to over 77 K.