SNS-DC-SQUIDs and flux transformers for integrated magnetometers in flip-chip technique

摘要

YBa2Cu3O7-δ/Ag/YBa2Cu3O7-δ Josephson-junctions across steps in MgO substrates were used to fabricate SNS-DC-SQUIDs in the step-and-gap geometry. The necessary break of the YBa2Cu3O7-δ-film at the step was confirmed by transmission electron microscopy investigations. The removal of the Ag-layer eliminates the shunt resistance on top of the HTSC which increases the normal resistance RN by more than two orders of magnitude with only a slight reduction in IC. The junctions can be described by the SINS-formalism, which allows high ICRN-products with large values of the normal resistances RN. For thin-film flux transformer epitaxial YBa2Cu3O7-δ/SrTiO3/YBa2Cu3O7-δ trilayers were grown using a co-sputter process. Test coils exhibited a current density in excess of 8×105 A/cm2 and insulation resistivities of 108 Ωcm at 77 K. By coupling the flux transformers to SQUIDs using a flip-chip technology the magnetic field response were increased by a factor of 9.