A low noise DC SQUID using edge junctions on c-axis oriented YBa2Cu3O7−x thin films

Abstract All YBa 2 Cu 3 O 7− x (YBCO) DC-superconducting quantum interference devices (SQUIDs) have been prepared using edge junctions between c -axis oriented YBCO films. The edge junctions were prepared with a natural barrier. The junctions were fabricated by an epitaxial multilayer sputtering process with patterning steps in between. The two superconducting layers were separated by an insulating epitaxial NdAlO 3 layer apart from the junction areas. The maximum flux-to-voltage conversion d V /dΦ was 30 μV/Φ 0 at 77 K with a regular modulation over many flux quanta Φ 0 . The equilivalent flux noise measured in the flux locked loop mode was 4.5 × 10 −5 Φ 0 / Hz 1 2 at 2 Hz and 1.5 × 10 −5 Φ 0 / Hz 1 2 above 40 Hz in the white noise region measured at 60 K. These results correspond to an energy resolution of 2 × 10 −28 J/Hz at 2 Hz and ϵ n,w ( f >40 Hz) = 2 × 10 −29 J/Hz at 60 K.