We have designed and fabricated three types of high- SQUID (superconducting quantum interference device) magnetometers based on step-edge Josephson junctions using three different concepts of coupling magnetic flux into the SQUID: (i) a single pickup loop galvanically coupled to the SQUID, (ii) a flux transformer inductively coupled to the SQUID and (iii) a multiloop pickup loop used directly as the SQUID inductance. On a substrate we achieved an effective flux capture area of and for the inductively coupled and multiloop devices, respectively. Due to the low white noise levels of for the inductively coupled magnetometer and for the multiloop device high quality magnetocardiograms were recorded inside a magnetically shielded room without signal averaging.
A multi-layer technology, based on YBaCuO as the superconducting material and SrTiO3 as the insulating material, is described. Patterning is performed by photolithography and Ar-ion-beam etching under fiat incidence. Using a resist bake-out prior to the etching, step angles in the patterned lower film of less than 20 degrees are obtained. Superconducting 10-turn thin-film coils have been fabricated with transition temperatures of up to 83 K and critical current densities at 77 K of 2*105 A cm-2. Furthermore we have fabricated a thin-film flux transformer and combined it in flip-chip configuration with a low-noise YBCO step-edge DC SQUID. We measured a magnetic field resolution of the complete magnetometer of 200 fT Hz-1/2 at 1 Hz, dominated by the SQUID noise itself.
A fully oxygen-compatible ion-beam sputter deposition process (IBS) has been implemented for investigation of four film/substrate couples: (103)/(110)YBCO on (110)SrTiO3 (STO) and on (100)NdGaO3 (NGO), and (100)/(010)YBCO on (110)NGO and on (100)STO. For comparison, some (103)/(110)YBCO films have also been prepared by off-axis rf-magnetron sputtering. Below about 600 °C semiconducting, sub-nm flat, and perfectly single-crystalline YBCO films crystallize on these substrates with a crystallographic unit cell of about 1/3 of the Cu-O subcell of YBCO and perfect registration with the Ti4+-O and Ga3+-O sublattice of STO and NGO, respectively. At higher temperature superconducting YBCO films grow coherently epitaxially in the first....
A modular, 9-channel high-Tc SQUID system for magnetocardiography (MCG) was developed and tested in an unshielded environment. Galvanically-coupled magnetometers made from Y-Ba-Cu-O films, with intrinsic white noise levels as low as 70 fT/√Hz, are used as SQUID sensors. In an unshielded environment, a noise level of about 1 pT/√Hz for each channel was achieved using an active noise compensation system. A new digital planar gradiometer is proposed. First magnetocardiograms recorded in an unshielded environment are presented