Highly sensitive YBa2Cu3O7 dc SQUID magnetometer with thin-film flux transformer

Abstract

We have designed and fabricated a thin-film flux transformer by a YBa2Cu3O7/SrTiO3 (YBCO/STO) multilayer process. The flux transformer consists of a 20-turn input coil of 10 μm linewidth and a single-turn pickup loop surrounding an area of 7.5 by 7.5 mm2. All device levels are patterned by standard photolithography and Ar-ion-beam etching. The flux transformer has been combined in flip-chip configuration with the square washer of a low-noise YBCO dc SQUID. The dc SQUID magnetometer exhibits a magnetic field sensitivity of 1.4 nT/Φ0. The intrinsic white flux noise level of 70μΦ0/√Hz at 77 K is mainly dominated by the SQUID corresponding to a magnetic field resolution of the magnetometer of 100 fT/√Hz for frequencies above 40 Hz. At 1 Hz we measured 200 fT/√Hz. Biomagnetic measurements were performed in a magnetically shielded chamber.

Performance of YBa2Cu3O7−δ direct current SQUIDS with high-resistance step-edge junctions

“…[1][2][3][4] The best flux noise and magnetic field resolution ͑in good magnetic shielding͒, approaching the performance of conventional, liquid-heliumcooled devices, were achieved by Lee et al using magnetometers fabricated from YBa 2 Cu 3 O 7Ϫ␦ ͑YBCO͒ thin epitaxial films with bicrystal junctions, i.e., on SrTiO 3 bicrystal substrates. [1][2][3][4] The best flux noise and magnetic field resolution ͑in good magnetic shielding͒, approaching the performance of conventional, liquid-heliumcooled devices, were achieved by Lee et al using magnetometers fabricated from YBa 2 Cu 3 O 7Ϫ␦ ͑YBCO͒ thin epitaxial films with bicrystal junctions, i.e., on SrTiO 3 bicrystal substrates.…”

Study of DyBaCuO DC SQUIDs for low noise and high flux focusing

“…Many SQUID devices for highly magnetic flux sensors, have also been investigated sufficiently sensitive for biomagnetic measurements and other applications [31,[41,[51. In this paper, we describe the fabrication and characteristics of a DC-SQUID using step-edge Josephson junctions (SEJs) on MgO substrates. 11. SQUID FABRICATION DC-SQUIDS using SEJs were fabricated on MgO substrates by Ar-ion beam etching and the MBE growing technique [6].…”

A novel multilayer circuit process using YBa2Cu3Ox/SrTiO3 thin films patterned by wet etching and ion milling

“…[1][2][3][4][5][6][7][8][9][10] In conjunction with HTS Josephson junctions, structures of this type are used in many superconducting applications such as dc SQUID flux transformers and Josephson digital circuits. Our process is suitable for these HTS multilayers circuits, since both upper and lower HTS layers have high crystalline quality even at crossovers and via connections and are well isolated by the intermediate epitaxial insulator.…”

“…2 This letter will focus on transport J c as the figure of merit in evaluating our process. Ion milling at an inclined incident angle combined with photoresist overbaking was used by several groups [3][4][5] to etch the bottom YBCO and the insulating STO layer for beveled steps. Another way to form low-angle crossovers is the use of shadow masks [6][7][8] ; however, this technique is not applicable for making via connections.…”