Fabrication of Ultrasmall High-Quality Bi2Sr2CaCu2O8+δ Intrinsic Josephson Junctions.

The fabrication of ultrasmall high-quality intrinsic Josephson junctions (IJJs) using a cuprate superconductor is critical for the realization of a qubit. We investigated the mechanism of damage induced by a Ga⁺ beam in a Bi₂Sr₂CaCu₂O_8+δ IJJ during focused ion beam (FIB) processing. On the basis of the results, we developed a process that allowed the successful fabrication of an ultrasmall and high-quality IJJ. The damage induced by the FIB is reduced by restricting the direction of the Ga⁺ beam so that the junction area is not directly irradiated by the ion beam. The fabricated ultrasmall IJJ device has a junction area of 0.3 µm² and shows excellent current–voltage characteristics. [ABSTRACT FROM AUTHOR]