DC-SQUIDS AND FLUX TRANSFORMERS IN YBA2CU3O7 MAGNETOMETERS AT 77 K

For biomagnetic applications magnetometer devices are prepared in a multilayer process based on KrF-excimer laser deposition of superconductor and insulator layers as well as semiconducting barriers. For patterning conventional photolithography and argon-ion etching are used. In the dc-SQUIDs we employ Josephson junctions with artificial barriers of PrBa2Cu3O7 in a ramp-type geometry. As insulating layers in the flux transformers we use SrTiO3. Both, the dc-SQUIDs and the input-coils operate up to temperatures of 86 K. The characterization of the devices is made by electrical transport and by noise measurements. For the use as sensitive magnetometers the dc-SQUIDS are either used in inductively shunted magnetometers with galvanic coupling to a large pick-up coil or are coupled to flux transformers in a flip-chip arrangement.