Multilayer technique developed for fabricating Nb-based single-electron devices

A reliable process has been developed for the fabrication of all-Nb single-electron circuits, based on spin-on glass planarization. The process steps are the in situ growth of Nb/AlOx/Nb sandwich, definition of the patterns of junctions, base electrodes and wiring by use of reactive ion etching and the planarization of a spin-on glass insulation between base electrode and wiring. A single electron transistor made of 0.1 square micrometer area junctions clearly shows the e-periodic Coulomb blockade modulation by a voltage applied to a gate.