Lateral tunnel junction produced by electron-beam-induced deposition

Electron-beam-induced deposition using a WF6 precursor molecule was applied to making metal/insulator/metal tunnel junctions for single-electron transport devices. Single wires 8 nm high and about 13 nm wide were produced on a SiO2 substrate with Au/Cr electrode pads and their conductance showed a rapid increase of about five orders of magnitude as electron-beam (EB) doses increased between 5 and 15 pC shot. To estimate the deposit thickness distribution, spatial thickness distribution in spot exposure was defined and obtained for specified EB doses. From this function, a single-wire resistivity at 230 and 300 K was determined to be 6x10(-4) Omega cm at doses exceeding 15 pC/shot. Single-tunnel junctions, where space with a 2.5 nm increment was at the center of single wire, were produced. The electrical characteristics of these single junctions were fitted to a Fowler-Nordheim plot the absolute value of whose gradient gradually increased with increasing space width. The barrier height of this junction was estimated to be 0.17-0.2 eV, lower than that for SiO2/W junctions. This might be caused by the change from the metallic deposit to the insulator for the single wire as a function of the EB dose. This deposition technique enabled us to fabricate a transistor structure where dots were located in space and a side gate electrode was also deposited. The structure showed Coulomb oscillation even at 230 K and Monte Carlo simulation of this device showed reasonable agreement with the experiment, assuming appropriate circuit parameters of gate capacitance and tunnel resistance. (C) 1997 American Vacuum Society.