FABRICATION AND CHARACTERIZATION OF SINGLE-ELECTRON TUNNELING TRANSISTORS IN THE SUPERCONDUCTING STATE

We have used electron-beam lithography to fabricate single electron charging effect devices with ultrasmall capacitance Al/Al2O3/Al tunnel junctions. The single electron transistor is a three terminal device comprised of two series tunnel junctions and a gate electrode capacitively coupled to the island between them. Typical junctions are of area 60 nm x 60 nm with a capacitance of 190 aF. We outline our fabrication procedures, discuss operational properties, and give sample handling considerations. These devices exhibit a highly nonlinear I-V characteristic which is modulated by the gate voltage, as expected for the Coulomb blockade. In the superconducting state, the superconducting gap in the quasiparticle density of states leads to transistor action above 1.3 K, a temperature easily reached with pumped liquid He-4 refrigeration. We also discuss the observation of an intermittent intrinsic switching noise in the offset charge of the central island.