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....
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.
We have fabricated YBa2Cu3O7 ramp-type junctions incorporating a barrier layer of NdGaO3 with a nominal thickness of 2 nm. The junctions exhibit pronounced Josephson effects and operate up to 82 K. The characteristics are well described within the resistively shunted junction model. We observe large hysteresis parameters βc even at elevated temperatures. The output voltage of a high-Tc dc SQUID is found to benefit from the intrinsic junction capacitance.
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.
D. Grundler, J. P. Krumme, B. David, and O. Dössel. YBa2Cu3O7 ramp-type junctions and superconducting quantum interference devices with an ultrathin barrier of NdGaO3. In Applied Physics Letters, vol. 65(14) , pp. 1841-1843, 1994
We have fabricated ramp-type Josephson junctions and SQUIDs (superconducting quantum interference devices) using an ultrathin barrier layer of NdGaO3 as weak contact between the YBa2Cu3O7 electrodes. The junctions operate up to 82 K, exhibiting current-voltage characteristics of the resistively-hunted-unction type. A normal-state resistance of up to....
Conference Contributions (1)
B. David, O. Dössel, D. Grundler, and J. P. Krumme. SQUID-Module aus Hoch-Tc-Supraleitern für die Magnetometrie. In Supraleitung und Tieftemperaturtechnik, zum Statusseminar, Berichte zu F&E-Projekten aus dem Förderbereich Physikalische Technologie des Bundesministeriums für Forschung und Technologie, pp. 79-85, 1994
Ziel des Forschungsvorhabens ist die Herstellung von SQUID-Anordnungen aus Hochtemperatur-Supraleitern (HTSL), mit denen die Messung biomagnetischer Signale möglich ist. Dazu werden Magnetometer bestehend aus Flußantennen und dc-SQUID-Sensoren aufgebaut, und zu elektronischen Gradiometern zusammengefaßt. Rauscharme dc-SQUIDs, basierend auf einer zuverlässigen Josephsonkontakt-Technologie und eine HTSL-Mehrlagentechnologie sind dafür eine notwendige Voraussetzung. Neben den routinemäßig verwendeten YBa2Cu3O7 (YBCO)-Stufen-Kontakten wurden SIS-Rampen-Kontakte entwickelt, die NdGaO3 als Barrierenmaterial verwenden