Single electron transistors with Nb/AlOx/Nb junctions

Abstract

Deep submicron Nb/AlOx/Nb tunnel junctions and single electron transistors were fabricated by electron beam gun shadow evaporation, using stencil masks consisting of the thermostable polymer polyethersulfone and germanium. The I(U) characteristics of the single electron transistors show special features due to the tunneling of single Cooper pairs and quasiparticles. Significant e-periodic gate modulation is observed in both the superconducting and the normal state and a gap energy Δeff of up to ≈1 meV has been achieved. The special features of using the refractory metal Nb in combination with the shadow evaporation technique are discussed.