Improved reproducible fabrication process of HTS-SQUIDs with ramp-edge Josephson junctions and multilayer structures

• Published in: Physica. C, Superconductivity Vol. 470; no. 20; pp. 1515 - 1519
• Main Authors: Adachi, S., Oshikubo, Y., Tsukamoto, A., Ishimaru, Y., Hato, T., Kawano, J., Tanabe, K.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2010; Elsevier
• Subjects: Applied sciences; Electronics; Exact sciences and technology; Flux noise; Gradiometer array; IcRn; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Magnetic components, instruments and techniques; Physics; Ramp-edge Josephson junction; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; SQUID; Superconducting devices; Gradiometer array; IcRn; SQUID; Flux noise; Ramp-edge Josephson junction; Surface cleaning; Dry etching; I; Background noise; Heat treatments; Superconducting coils; Fabrication; Multilayers; R; SQUID magnetometers; High-Tc superconductors; Coated conductor; Josephson junctions; Step edge junction
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2010.05.152

We have studied the fabrication process for high-Tc superconducting quantum interference devices (HTS-SQUIDs) containing ramp-edge-type Josephson junctions and multilayer superconducting wiring. 5-Channel gradiometer arrays for non-destructive evaluation of striated coated conductors were fabricated. Our previous process contained some problems which often brought about property spreads of the gradiometers and/or degradation in superconducting electrodes. We attempted to improve homogeneity of substrate temperature during barrier preparation. The thickness of a black-colored Pr1.4Ba1.6Cu2.6Ga0.4Oy embedded at the lowest in the multilayer was increased. The substrate on which bare ramp-surfaces were arranged was heated from the rear side by thermal radiation. A sapphire plate as a temperature homogenizer was inserted between the substrate and the heater. At the final procedure of the process, careful oxygenation containing surface cleaning by dry etching prior to heat-treatment was carried out. By employing them, five HTS-SQUIDs exhibiting the peak-to-peak modulation voltage over 50μV were successfully fabricated within 6×6-mm2 area in a chip. Their noise levels at 1kHz and 77K were as low as 4μΦ0/Hz1/2.