Nanolithography by non-contact AFM induced local oxidation : Fabrication of tunneling barriers suitable for single electron devices

TL;DR

This paper demonstrates a non-contact AFM-based nanolithography method to create ultra-fine tunneling barriers for single-electron devices, achieving high precision and well-defined electrical properties.

Contribution

It introduces a novel AFM-induced local oxidation technique with optimized tip design for fabricating nanoscale tunneling barriers.

Findings

Fabricated Ti/TiOx line grids with 18 nm period.

Achieved tunneling barriers as small as 15 nm.

Observed exponential conductance dependence indicating tunneling.

Abstract

We study local oxidation induced by dynamic atomic force microscopy (AFM), commonly called TappingMode AFM. This minimizes the field induced forces, which cause the tip to blunt, and enables us to use very fine tips. We are able to fabricate Ti/TiOx line grids with 18 nm period and well defined isolating barriers as small as 15 nm. These junctions show a non-linear current-voltage characteristic and an exponential dependence of the conductance on the oxide width, indicating tunneling as the dominant conduction mechanism. From the conductance - barrier width dependence we derive a barrier height of 178 meV. Numerical calculations of the lateral field distribution for different tip geometries allow to design the optimum tip for the most localised electric field. The electron-beam-deposition (EBD) technique makes it possible to actually produce tips of the desired geometry.