Characterization of all-Nb nanodevices fabricated by electron beam lithography and ion beam oxidation

The authors present a reliable process that allows them to fabricate all-niobium nanodevices in a reproducible and well controlled way. Deposition of niobium thin films is done through a suspended mask formed in a Ge layer supported by a thermally stable polymer called phenylene-ether-sulfone, while the tunnel barrier is formed by ion beam oxidation of Nb surface. They study the effect of the fabrication conditions on the quality of narrow Nb stripes by measuring their transition temperature. Using dc transport measurements, they characterize tunnel junctions as well as single-electron transistors (SETs) and extract basic junction parameters, such as the barrier height, width, and specific capacitance. Low-frequency charge noise of all-Nb SETs at 50mK50mK has a 1∕f1∕f power spectrum and the value of ∼4×10−3e/Hz1∕2∼4×10−3e∕Hz1∕2 at 1Hz1Hz