Large-area nanogap fabrication for terahertz switching

Abstract

Here, I will introduce new lithography techniques that fabricate an array of metal gaps of nanometer to Ångstrom scale. Furthermore, the related optical applications in the terahertz (THz) region are also covered. A fundamental challenge was to fabricate THz‐resonant nano-patterns over, at least, a square sub-millimeter. At the beginning of these studies, the focused ion beam and electron-beam lithography techniques were used for fabricating the THz‐resonant nanostructures such as nano-slot antennas and cloased-loop nano-gaps, but the fabrications with those techniques were expensive and slow. To overcome these fabrication issues, new lithography techniques such as nanoimprint, nanosphere lithography, and atomic layer lithography have recently been developed for large‐area nanogap arrays in thin metal films. In particular, atomic layer lithography, which combines atomic layer deposition with standard lithography techniques, produced an array of nanogaps with gap widths of 1 nm in metal films over a wafer-scale substrate. Funneling of THz waves through the resulting 1 nm gaps led to a record field enhancement factor of 25 000. THz waves and nanometer gaps have become a great combination for dramatically enhancing light–matter interactions by contacting the large-area nanogaps to the phase-transition materials.