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

• We develop a X-ray lithography based fabrication process.
• We fabricate multiple large chips of split ring resonators on transparent substrate.
• The optical response of the structure has been measured by ellipsometry.
• A detection test of a monolayer of thiols has been performed.
• The SRR geometry is a promising sensing structure.

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 × 1 mm, over a surface area of 12 × 18 mm. 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.

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