Fabrication of weak-link Nb-based nano-SQUIDs by FIB process

We develop a fabrication process of a Nb-based nano-SQUID (superconducting quantum interface devices). Our SQUID consist of two weak-link Josephson junctions, and the SQUID was patterned by a FIB (focused ion beam). Typical dimension of the SQUID diameter was 1 μm, and widths of the weak links were from 60 to 500 nm. To evaluate the degradation of Nb, we compared characteristics of SQUID made by bilayer films and single Nb layer. Our experimental data shows that the normal metal on Nb layer successfully works as the protection layer by the FIB process. We develop a fabrication process of Nb-based nano-SQUIDs (superconducting quantum interference devices) containing two weak-link Josephson junctions patterned by a focused ion beam (FIB). Typical dimension of the SQUID diameter was 1 μm, and the widths of the weak links were changed in the range of 60 and 500 nm. In order to evaluate the degradation of Nb due to the FIB process, we employed bilayer films of Nb/Au and Nb/W in addition to single layer Nb films. The lateral degradation depths of 85 nm for Nb and 27.5 nm for Nb/Au and Nb/W indicate that the normal metals successfully work as the protection layer. The magnetic field dependence of the critical current showed the modulation ratio of about 10%.