Fabrication and optimization of rf-SQUID and SQUID integration assembly for high resolution magnetic imaging systems

Abstract

Superconducting QUantum Interference Devices or SQUIDs are by far the most sensitive devices known for sensing magnetic flux down to a resolution of about 10−21Wb and finds innumerous applications in various fields. In order to apply these sensors to sense nano structures or to use in antibody or antigen ammunoassay experiments, especially in unshielded environments at Liquid Nitrogen temperatures, one needs to optimize the SQUIDs for high SNR and low background magnetic field sensitivity. The chief motivation for this research work and this thesis is to optimize and characterize HTc rf-SQUIDs so that high field sensitivity and high spatial resolution could be obtained. During the course of this study, rf-SQUIDs were fabricated using SEJ and Bicrystal technology and optimized for the above mentioned characteristics. In the next stage, these optimized sensors were integrated into an imaging system after a thorough investigation on problems related to the front-end assembly of such a system. Different SQUID microscope systems have been designed, fabricated, and tested in order to achieve high field sensitivity and high spatial resolution magnetic imaging under the constraint of keeping the sample at room temperature, while the SQUID is in Liquid Nitrogen Temperature. Using the developed systems, magnetic imaging of room temperature samples with sensitivities in the range of about 100fT/√ (Hz) and spatial resolution of about 100 µm were achieved