Nano-gap electrodes developed using focused ion beam technology

Abstract

Maskless fabrication methods for nanogap electrodes using sputter etching with a Ga focused ion beam (FIB) are presented. These methods are based on the in situ monitoring of the etching steps by measuring the current through patterned electrode films. The etching steps were terminated electrically at a predetermined current level. In the present experiment, a 30-keV Ga FIB with a beam size of ˜12 nm was irradiated on double-layered films consisting of a 10-30-nm-thick Au top electrode layer and a 1-2-nm-thick Ti bottom adhesion layer to form nanowires and nanogaps. Electrode gaps that were much narrower than the beam size could be reproducibly fabricated using the presented method. The controllability of the fabrication steps was significantly improved by using triple-layered films consisting of a thin Ti top layer, Au electrode, and a bottom Ti adhesion layer. The minimum gap width achieved was ˜3 nm, and the fabrication yield reached ˜90 % for ˜3-6-nm wide gaps. Most of the fabricated nanogap electrodes showed high insulating resistances, ranging from 1 GὨ to 1 TὨ. The applicability of the fabricated nanogap electrodes to electron transport studies of nanometer-sized objects was examined using electrical measurements of Au colloidal nanoparticles.