High-Tc Low-Noise dc SQUIDs Operating at 77K

We have used a superconductor-normal metal-superconductor (SNS) step-edge technique to produce low-noise dc SQUIDs operating at 77 K. The device fabrication process is both reproducible and manufacturable, and is targeted for commercial use. The superconductor is YBa2Cu3O7−δ and the normal metal is typically a Ag-Au alloy. At 77 K, the energy sensitivity for the SQUIDs with the smallest inductance, L = 12 pH, reaches below 9 × 10−30 J/Hz at 1 Hz and is 8 × 10−29 J/Hz at 100 Hz. The energy sensitivity for larger SQUIDs with L = 70 pH is 5 × 10−29 J/Hz at 1 Hz and 3 × 10−29 J/Hz at 100 Hz, values that are sufficient for many practical applications. A multi-level high-Tc technology has also been developed. This has resulted in the fabrication of a SQUID magnetometer consisting of a washer-style SQUID coupled to a multi-turn input coil and a large area pickup coil, all on the same substrate.