Thin film HTc SQUID construction and characterisation

The authors describe the process for manufacturing DC superconducting quantum interference devices (SQUIDs) using both step junctions and 45 degrees -rotated grain boundaries. An assessment of the noise performance and flux-to-voltage ratio for fourteen devices of various inductances, operating temperatures, and junction technologies is given. Systematic experiments on the technology steps required to construct fully integrated magnetometers and gradiometers are described. These include crossovers, superconducting interconnects, and film growth on undulating surfaces. For each of these, test structures have been constructed, and their properties have been measured. A simplified three-layer fully integrated DC SQUID magnetometer design is described. The authors highlight the need for improved reproducibility and demonstrate that, for a number of devices, there is no obvious relation between the temperature and the magnetic flux noise. The process for constructing interlayer superconducting contacts is shown to work, and the insulator has sufficient resistance for flux transformer applications.<
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