Maskless fabrication of nanoelectrode structures with nanogaps by using Ga focused ion beams

Maskless fabrication techniques of nanoelectrode with nanogaps are investigated, which use sputter etching technique by Ga focused ion beam (FIB). The etching steps are reliably controlled in situ by monitoring a current fed to the films. 30 keV Ga FIB with a beam size of 12 nm is irradiated on double layer films consisting of 10-30 nm thick Au top conducting layer and 1-2 nm thick Ti bottom adhesion layer to form nanowires and gaps. The films are deposited on a silicon substrate on which 200 nm of oxide has been thermally grown and patterned to define 5-7 μm wide strips by photolithography and Ar sputter etching. By the present techniques nanogaps with a width much smaller than a beam diameter are fabricated. The minimum gap width of ∼3 nm and the highest gap resistivity of ∼80 GΩ are obtained.