Ion Irradiation–Induced Modification of Electrical Properties of YBa2Cu3O7-x NanoSQUIDs

We report on the fabrication and characterization of nanopatterned superconducting quantum interference devices (SQUIDs) based on bi-crystal MgO with 24° misorientation angle in epitaxially grown YBa2Cu3O7−δ thin films. Nanopatterning is performed by Ga+ focused ion beam milling. We present a study of the effect of ion irradiation–induced modification of electrical properties of YBa2Cu3O7−δ nanoSQUIDs to uncover the performance of the nanoSQUIDs without Au as shunting layer, which have potential to reduce the intrinsic thermal flux noise. In this experiment, seven YBCO nanoSQUIDs are fabricated and measured under liquid helium temperature. The statistical results of I–V characteristics illustrate that the properties of YBCO nanoSQUIDs without Au as protection layer are sensitive to ion beam irradiation during focused ion beam (FIB) cutting process. As a consequence, the critical current Ic changes between 10.3 and 107 μA with resistance 120 Ω and 16.5 Ω respectively. In other words, the SQUID voltage is almost stable. Surprisingly, none of them shows hysteresis I–V characteristics even the resistance up to 120 Ω, which is not the case for YBa2Cu3O7−δ nanoSQUIDs based on SrTiO3 bi-crystal. In view of above-mentioned, we propose to deposit one insulating layer as protection layer around grain boundary of MgO to avoid the degradation of critical current and increase the resistance.