Fabrication and physics of similar to 2 nm islands for single electron devices

Multiple tunneling junctions consisting of metal islands about 2 nm in diameter and < 2 nm gaps were fabricated by a combination of high resolution electron-beam lithography and an ionized beam deposition technique. The effective tunneling capacitance of this structure is calculated to be about 0.2 aF, implying that the charging energy associated with an electron tunneling on or off the islands is well above the thermal energy at room temperature. Electrical measurements showed clear Coulomb blockade effects in this structure. Coulomb gaps of 0.16 V were observed at 77 K in the source-drain current-voltage characteristics and the nonlinearity persisted up to room temperature although the Coulomb gaps disappeared as the temperature was raised. When the voltage applied to the gate electrode was swept, the drain-source current showed strong oscillations at constant drain-source bias voltage, confirming the existence of single electron charging effects. This process can be used to fabricate single electron devices operating at liquid nitrogen temperature or perhaps even at room temperature and is compatible with the methods used in integrated circuit processes. (C) 1995 American Vacuum Society.