Fabrication of multiple large arrays of split ring resonators by X-ray lithographic process for sensing purposes

Abstract

In this paper we present the fabrication of multiple, large arrays of nano-metric split ring resonators, having variable aspect ratio, in order to obtain a sample suitable for prism-free plasmonic sensing applications. It has been shown that high aspect ratio structures present a richer longitudinal plasmonic resonant response, compared to thin geometries. In order to produce a platform suitable also for parallel measurements, the split ring resonators were arranged in ten square arrays, having an area of 1×1mm, over a surface area of 12×18mm. To obtain this result, we developed a fabrication process based on X-ray lithography. The choice of X-ray lithography as the main technique is justified by the possibility to obtain higher aspect ratio and to achieve large areas arrays of nano-structures in a single, fast exposure, compared to other techniques, such as Nanoimprint Lithography or Electron Beam Lithography. A new X-ray mask design was developed for achieving the ten large chips design. The fabricated split ring resonator arrays have been characterized by ellipsometric transmittance measurements in the visible and near-infrared range. The strong dependence of the split ring resonant response to the polarization of the impinging light, has been exploited to perform a test of the detection properties of the structure, functionalized with a mono-layer of self assembled dodecanethiols. The encouraging results of the detection test indicate the SRR geometry as a promising sensing structure.