Magneto-optical studies of high-T(c) SQUID circuits

Magneto-optical studies have been carried out on high-T(c) thin film circuits such as flux transformer coils and DC SQUIDs. The high resolution magnetic field maps emphasize regions of high field and localized defects. Observation of the flux transformer coil response to an applied field allowed a determination of the minimum critical current. An inversion procedure is also described for calculation of the current distributions in the patterned coil films. The images of DC SQUIDs fabricated on bicrystal substrates show the effects of flux penetration through the bicrystal boundary. The noise performance of the coils while flip-chip coupled to the bicrystal DC SQUIDs is also summarized. The research has provided information useful for improvements to multi-level high-T(c) circuit design and fabrication