FABRICATION AND CHARACTERIZATION OF SINGLE-ELECTRON TRANSISTORS BASEDON AL ALOX/AL AND NB/ALOX/NB TUNNEL-JUNCTIONS/

The SAIL (self-aligned in-line) technique has been applied to the prep aration of ultrasmall metallic tunnel junctions. By using e-beam litho graphy and sputter methods the area of both Al/AlOx/Al and Nb/AlOx/Nb contacts has so far been reduced to less than 0.005 mu m(2). At low te mperatures high-ohmic double junctions with a small metallic island in between show the Coulomb blockade effect. The current through such a device can be modulated by a voltage applied to a gate electrode capac itively coupled to the island (single-electron transistor). Both these single-charge phenomena have been observed at temperatures of a few h undred mK.