Series Arrays of Long Josephson Junctions Fabricated with a Focused Helium Ion Beam in YBa2Cu3O7-δ

We investigated series arrays of closely spaced, planar long Josephson junctions for magnetic flux transduction with a linear response and high dynamic range. The devices were fabricated from 30-nm thick high-temperature superconducting YBa
₂
Cu
₃
O
_7-δ
(YBCO) thin films, using focused helium ion beam irradiation to create the Josephson barriers. Series arrays consisting of 600 long junctions, were fabricated and electrically tested. From fits of the current-voltage characteristics we estimate the standard deviation in critical current to be around 25%. Voltage-magnetic field measurements exhibit a sharp transfer function with a modulation depth of 11 mV over a range of 135μ T at 71 K.