Fabrication and properties of high performance YBa_2Cu_3O_(7?δ) radio frequency SQUIDs with step-edge Josephson junctions

We describe the fabrication of high performance YBa_2 Cu_3 O_(7?δ) (YBCO) radio frequency (RF) superconducting quantum interference devices (SQUIDs), which were prepared on 5 mm×5 mm LaAlO_3 (LAO) substrates by employing stepedge junctions (SEJs) and in flip-chip configuration with 12 mm×12 mm resonators. The step in the substrate was produced by Ar ion etching with step angles ranging from 47° to 61°, which is steep enough to ensure the formation of grain boundaries (GBs) at the step edges. The YBCO film was deposited using the pulsed laser deposition (PLD) technique with a film thickness half of the height of the substrate step. The inductance of the SQUID washer was designed to be about 157 pH. Under these circumstances, high performance YBCO RF SQUIDs were successfully fabricated with a typical flux-voltage transfer ratio of 83 mV/Φ_0, a white flux noise of 29 μΦ_0 /~(1/2) Hz, and the magnetic field sensitivity as high as 80 fT/~(1/2)Hz. These devices have been applied in magnetocardiography and geological surveys.supported by the National Basic Research Program of China,the National Natural Science Foundation of China,the Research Fund for the Doctoral Program of Higher Education, China中国科技核心期刊(ISTIC)中国科学引文数据库(CSCD)9097401-1-097401-42