Long-time stable HTSC DC-SQUID gradiometers with silicon dioxide passivation for measurements with superconducting flux transformers

TL;DR

This paper presents the design and long-term stability analysis of high-temperature superconducting DC-SQUID gradiometers with silicon dioxide passivation, demonstrating reliable performance over a year for biomagnetic and magnetic nanoparticle applications.

Contribution

It introduces a stable, long-term operational HTSC DC-SQUID gradiometer with SiO2 passivation and compares flux transformer materials in shielded and unshielded environments.

Findings

Achieved low white field gradient noise of 72 fT/(cm√Hz) with TBCCO on LaAlO3

Sensor parameters remained stable over one year, indicating high durability

Demonstrated effective protection against atmosphere and humidity effects

Abstract

In applications for high-Tc superconducting DC-SQUIDs such as biomagnetism, nondestructive evaluation and the relaxation of magnetic nanoparticles, it is important to maintain reliable sensor performance over an extended time period. We designed and produced DC-SQUID gradiometers based on YBCO thin films which are inductively coupled to a flux transformer to achieve a higher sensitivity. The gradiometers are protected against ambient atmosphere and humidity by SiO2 and amorphous YBCO layers. The noise properties of the sensor in flip-chip configuration, especially in unshielded environments, are shown. We present a comparison of TBCCO thin films on buffered sapphire or LaAlO3 substrates for the flux transformer in shielded and unshielded environments. We reach a low white field gradient noise of 72 fT/(cm sqrt(Hz)) with the TBCCO on LaAlO3 flux transformer. The electric properties of the gradiometers (critical current IC, normal state resistance RN and the transfer function VPhi) were measured over a period of one year and do not show significant signs of degradation.