NanoSQUIDs With Proximity Effect Nanobridge Josephson Junctions for Future Applications in Electron Microscopy

Nanoscale superconducting quantum interference devices (nanoSQUIDs) with nanobridge Josephson junctions (nJJs) were prepared on SiN membranes for experiments with transmission electron microscope (TEM) at temperatures below 10 K. As thin-film materials for the nanobridges, metals Ti and Nb were combined into 3-layer heterostructures for adjusting superconducting parameters of the nJJs through the proximity effect. This allowed to reduce spread of parameters in ultrathin superconducting films and to adjust operating temperature of nJJs to the optimum operating temperature of the commercial TEM sample holders cooled using liquid helium. Electron beam lithography and high selectivity reactive ion etching with pure SF₆ gas were used to pattern nJJs with down to 10 nm width that is comparable to coherence length in thin films of Nb. Measurements revealed non-hysteretic I(V) characteristics of the nJJs and nanoSQUIDs. The paper is mainly devoted to the development of nanoSQUIDs for possible applications in TEM. Towards realization of hybrid superconductor-ferromagnetic nanostructures for further experiments in TEM, Permalloy triangles with spatial resolution down to ∼100 nm were prepared on similar SiN membranes and studied by Lorentz TEM method. These technologies are promising for the fabrication of superconducting electronics based on nJJs for operation inside a TEM.