Single-Step Grayscale Lithography of Multi-Depth Mie Void Metasurfaces

Abstract

The height of dielectric metasurfaces is largely considered a constant in the fabrication process due to the top-down fabrication approach, resulting in a binary structure. Yet, for the recently introduced Mie voids metasurfaces, controlling the thickness of the voids locally is crucial for achieving significant spectral tuning. In this work we demonstrate Mie voids metasurfaces with local precise depth control using electron beam grayscale lithography. We underexpose PMMA with varying doses, which in turn translates to multiple depth levels in the developed resist. Transferring the pattern to a silicon substrate we generate Mie voids, trapping the light in the void which generates colors in reflection. By controlling the depth of the void at the nanoscale, we tune the resonance over the whole visible range and with high precision, resulting in a large gamut of colors, which is demonstrated with spectral measurements, images of uniform patterns and spatially varying patterns showcasing different geometrical designs and a detailed artistic image. The demonstrated approach can be used for the implementation of various types of dielectric metasurfaces, providing an additional important degree of freedom for their realization, with potential applications in structured light and structural colors, imaging, robotics, polarization control, sensing, virtual reality and more.