Low-Noise Serial High- $T_{c}$ $\hbox{YBa}_{2}\hbox{Cu}_{3}\hbox{O}_{y}$ Superconducting Quantum Interference Devices Based on Bicrystal Junctions

Abstract

The fabrication of high-T c YBa 2 Cu 3 O y (YBCO) superconducting quantum interference devices (SQUIDs) that produce low flux noise while maintaining a high fabrication yield continues to challenge scientists. In this paper, we report the characterization of low-noise serial high-T c SQUIDs for biomagnetic applications. Epitaxial high-T c YBCO thin films with a root-mean-square surface roughness less than 5 nm are optimized for the low-noise serial SQUID coupled to a common pickup coil to form magnetometers and gradiometers. Current-voltage curves, voltage-flux curves, and flux noise of SQUID devices are characterized. A smooth surface morphology across the bicrystal line is essential for SQUIDs to show good characteristics. The field sensitivity is improved by a factor of (2) 1/2 with the designed serial SQUID array, which is coupled to a common pickup loop. This is demonstrated, and its fabrication yield is higher than 80% for devices with peak-to-peak voltage V PP ≥ 15 μV. The challenges and perspectives of the high-T c serial SQUID array for biomagnetic applications are addressed and discussed.

Evaluation of realistic layouts for next generation on-scalp MEG: spatial information density maps

“…Until recently low critical temperature superconducting quantum interference devices (low- T c SQUIDs) were the only sensors that were commercially attractive for MEG systems because they uniquely combined high sensitivity with fabrication reproducibility. Recently, fabrication techniques have matured for high critical temperature (high- T c ) SQUIDs with improved reproducibility 1 , 2 and sensitivity 3 – 5 and new sensor technologies such as optically-pumped magnetometers (OPMs) 6 , diamond Nitrogen-vacancy center (N-V center) magnetometers 7 , giant magneto-resistance (GMR) based hybrid magnetometers 8 , 9 , and kinetic inductance magnetometers (KIMs) 10 have challenged the use of low- T c SQUIDs in the next generation of MEG systems. Such new alternatives are attractive as they enable MEG with reduced head-to-sensor standoff (i.e., on-scalp MEG) because they require less extreme operating temperatures than conventional low- T c SQUIDs (KIMs are the exception because they have yet to be demonstrated in high- T c technology).…”