Low specific capacitance by ion-beam oxidation of Niobium-based Josephson tunnel junctions

Josephson tunnel junctions were fabricated on niobium by ion-beam oxidation where an oxide thickness independent of the processing time can be achieved. Low specific capacitance of about 5 µF/ cm
²
at a maximum current density of 1 kA/cm
²
have been measured via junction and interferometer resonances. A model for the structure of those low-capacitance barriers is proposed.