Fabrication of high-aspect-ratio SiO₂ nanopillars by Si thermal oxidation for metalenses in the visible region

Abstract

We propose a fabrication method of metalenses in the visible region with high-aspect-ratio SiO2 nanopillars by thermal oxidation of Si nanopillars. We first evaluated the expansion of the nanopillars in width due to thermal oxidation, which affects the phase shift on metalenses. Next, considering expansion due to thermal oxidation and processing errors, a metalens pattern was fabricated, and the pillar width distribution was measured. The highest aspect ratio was 8.7. Finally, the focusing of the fabricated reflective metalens was confirmed, which indicates that the proposed method can fabricate metalenses in the visible region with SiO2 nanopillars including a transmissive metalens.

Image Processing Using High‐Index Dielectric Metasurfaces Based on Fano Resonance

“…[12][13][14] The fabrication process of Si nanopillar array covered by SiO 2 medium is a topic of interest for various optical biosensing applications. [23][24][25] This process consists of four steps [23] : First, colloidal silica (SiO 2 ) spheres are self-assembled on a Si substrate using colloidal lithography technique. The size and density of the spheres can be controlled by adjusting the concentration and spin-coating parameters of the colloidal solution.…”

“…This method can produce SiO 2 coated Si nanopillar arrays with different diameters and periods, which can be used to create metasurfaces for manipulating incident light in the visible region. [24] The proposed MSs were simulated by a full-wave numerical simulator, CST Studio Suite, where periodic boundary condi-tions were considered for both the x and y axes of each unit cell. Furthermore, they were illuminated by two Floquet ports from the top (+z) and bottom (−z) directions to get transmission spectra (T ss or S 21 ) of each unit cell.…”

“…This method can produce SiO 2 coated Si nanopillar arrays with different diameters and periods, which can be used to create metasurfaces for manipulating incident light in the visible region. [ 24 ]…”

“…It is worth noting that we chose two materials Si and SiO 2 for MS structures due to their large difference in their refractive index in addition to providing high refractive index values [12][13][14]. The fabrication process of Si nanopillar array covered by SiO 2 medium is a topic of interest for various optical biosensing applications [23][24][25]. This process consists of four steps[23] : First, colloidal silica (SiO 2 ) spheres are self-assembled on a Si substrate using colloidal lithography technique.…”