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.

We have fabricated high-Tc SQUID magnetometers with a pickup coil and a multiturn input coil integrated onto the same substrate. A four-channel system operating in liquid nitrogen has been developed and used to measure biomagnetic signals emanating from both the heart and the brain. The magnetic field sensitivity of the integrated SQUID magnetometer reaches 70 fT/√Hz at 1 kHz and 280 fT/√Hz at 1 Hz. The use of superconductor-normal metal-superconductor (SNS) step-edge junctions with YBa2Cu3O7−δ as the superconductor and Ag–Au alloy as the normal metal allows the measurements to be performed with standard dc bias electronics.

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