Technology, properties and applications of graphoepitaxial high-Tc SQUIDs

Tuesday 29 Oct 2013, 15:00 → 16:00 Asia/Tokyo

RIBF Bldg. Room 203 (RIKEN WAKO)

加速器セミナーのお知らせ 日時：2013年10月29日（火）15:00- 場所：RIBF棟203号室 講師：Dr. habil. M.I.Faley (Peter Grünberg Institute (PGI-5: Microstructure Research) Forschungszentrum Jülich GmbH) タイトル：Technology, properties and applications of graphoepitaxial high-Tc SQUIDs 概要： A new technology of fabrication of high-Tc Josephson junctions and SQUIDs based on graphoepitaxial growth of YBCO films and heterostructures on MgO substrates and step edges will be described. The 500 nm high steps on MgO substrates for high-Tc step-edge Josephson junctions were prepared using a two-part milling process with Ar ion beam etching. The technique of sputtering at high oxygen pressures (1 - 4 mbar) was used to provide a smart and homogeneous on-axis in-situ deposition of high-quality metal-oxide thin films from stoichiometric targets on step edges on MgO substrates. The in-plane orientation of grains in the YBCO films and heterostructures on the MgO step edges was realized by using textured and buffered substrate surfaces to achieve the graphoepitaxial growth of YBCO films with orientation of the a- and b-axis along the projections of the [100] and [010] crystallographic directions of MgO on the various substrate surfaces. The structure of the texture on the surface of the step edges was observed by atomic force microscopy. The in-plane orientation of the grains in the YBCO films was determined by observation of orientation of growth spirals on the surface of YBCO films by scanning electron microscopy. The orientation of c-axis of the YBCO films was determined by the high-resolution transmission electron microscopy. The c-axis of the YBCO films was oriented parallel to the [011] orientation of the MgO at the step edge and parallel to the [001] orientation on the rest of the substrate. The SQUIDs with graphoepitaxial step edge Josephson junctions on single crystal MgO substrates have demonstrated good reproducibility and quality. A normal state resistance Rn » 20 ohm, IcRn » 0.6 mV at 77 K and an RSJ-like current-voltage characteristics with McCumber parameter bC » 0.4 were obtained. The DC SQUIDs having graphoepitaxial step edge Josephson junctions showed voltage swings dVpp of about 60 µV at 77 K. The SQUIDs were combined with about 1-µm thick graphoepitaxial superconducting multilayer flux transformers to construct helium-free magnetometers for geomagnetic survey and magnetoencephalography having sensitivity of about 5 fT/ÖHz at 77 K. More than 100 magnetic field measurement systems for different applications worldwide were equipped with the sensitive high-Tc SQUIDs made in Jülich. 担当：渡邉（環) , 今尾