Investigation of multiple SQUID arrangements in single layer high T/sub c/ magnetometers

Abstract

Single layer high T/sub c/ dc SQUID sensors on bicrystal substrates were investigated. Special attention was paid to achieve a large flux-to-voltage transfer function in order to ensure stable operation of the SQUID electronics and to get low flux noise even in disturbed environment. Josephson junctions on 30/spl deg/ bicrystal were tested as well as sub-/spl mu/m junctions an 24/spl deg/ bicrystals. The steep edges achieved by sub-/spl mu/m patterning increased the resistance of the superconducting structures against large external fields. The design for large flux-to-voltage transfer functions focused on multiple de SQUID arrangements. For magnetometers with a directly coupled pickup-loop three junction SQUIDs show no advantage compared to standard two junction SQUIDs, but the series connection of two ordinary dc SQUIDs does. Although for magnetometers with inductively coupled pickup-loop twenty SQUIDs in series were used the effect on the flux-to-voltage transfer coefficient was poor, due to differences in the critical current and inductance of individual SQUIDs. The sensitivity of the whole magnetometer achieved with inductively coupled single layer pickup-loops is much smaller than with directly coupled ones. For the latter a pickup-loop formed as a conventional square washer shows better results compared to a slotted square.