A MULTILAYER PROCESS FOR THE FABRICATION OF HTSC FLUX TRANSFORMERS AND SQUIDS

A multi-layer technology, based on YBaCuO as the superconducting mater ial and SrTiO3 as the insulating material, is described. Patterning is performed by photolithography and Ar-ion-beam etching under flat inci dence. Using a resist bake-out prior to the etching, step angles in th e patterned lower film of less than 20-degrees are obtained. Supercond ucting 10-turn thin-film coils have been fabricated with transition te mperatures of up to 83 K and critical current densities at 77 K of 2 x 10(5) A cm-2 . Furthermore we have fabricated a thin-film flux transf ormer and combined it in flip-chip configuration with a low-noise YBCO step-edge DC SQUID. We measured a magnetic field resolution of the co mplete magnetometer of 200 fT Hz-1/2 at 1 Hz, dominated by the SQUID n oise itself.