A silicon-on-insulator vertical nanogap device for electrical transport measurements inaqueous electrolyte solution

Abstract

A novel concept for metal electrodes with few 10 nm separation for electrical conductancemeasurements in an aqueous electrolyte environment is presented. Silicon-on-insulator(SOI) material with 10 nm buried silicon dioxide serves as a base substrate for theformation of SOI plateau structures which, after recess-etching the thin oxide layer,thermal oxidation and subsequent metal thin film evaporation, feature vertically orientednanogap electrodes at their exposed sidewalls. During fabrication only standard siliconprocess technology without any high-resolution nanolithographic techniques is employed.The vertical concept allows an array-like parallel processing of many individual devices onthe same substrate chip. As analysed by cross-sectional TEM analysis the devices exhibit awell-defined material layer architecture, determined by the chosen material thicknesses andprocess parameters. To investigate the device in aqueous solution, we passivated the samplesurface by a polymer layer, leaving a micrometre-size fluid access window to the nanogapregion only. First current–voltage characteristics of a 65 nm gap device measured in60 mM buffer solution reveal excellent electrical isolation behaviour which suggestsapplications in the field of biomolecular electronics in a natural environment.