Advanced HTS dc SQUIDs with step-edge Josephson junctions for geophysical applications
in: IEEE Transactions on Applied Superconductivity (2018)
For ground-based electromagnetic methods in geophysics, dc Superconducting Quantum Interference Devices based of high temperature superconductors are well suited as magnetic field sensors. Therefore, we introduce in this work an advanced fabrication technology for HTS dc SQUIDs based on step-edge Josephson junctions. The dc SQUIDs are prepared on structured MgO substrates. A trilayer of YBCO/STO/YBCO is deposited by pulsed laser deposition and structured with ion beam etching. The galvanometer-type design consists of four different dc SQUIDs directly coupled to a pickup loop. They exhibit large IcRn products and a voltage swing of more than 30 µV. The magnetic field noise amounts to about 20 fT/Hz1/2 and 35 fT/Hz1/2 for the white noise region as well as 25 fT/Hz1/2 and 100 fT/Hz1/2 at 100 Hz for ac-bias and dc-bias SQUID electronics, respectively. The advanced fabrication process thus enables to produce HTS dc SQUIDs intended for the use in geophysical applications with high throughput.