Fabrication of Infrared Broadband Polarized Emitting Metasurfaces using Microsphere Photolithography

This paper describes the low-cost, scalable fabrication of 2D metasurface LWIR broadband polarized emitter/absorber. A Frequency Selective Surface (FSS) type design consisting of dipole antenna elements is designed for resonance in the 7.5-13 μm band. Frequency-domain Finite Element Method (FEM) is used to optimize the design with ellipsometrically measured properties. The design is synthesized to be broadband by hybridizing the dipole modes with phonon resonances in a germanium/silica dielectric which separates metallic elements froma continuous ground plane. While IR metasurfaces can be readily realized using direct-write nanofabrication techniques such as E-Beam Lithography, or Focus-Ion Beam milling, or two-photon lithography, these technologies are cost-prohibitive for large areas. This paper explores the Microsphere Photolithography (MPL) technique to fabricate these devices. MPL uses arrays of self-assembled microspheres as optical elements, with each sphere focusing flood illumination to a sub-wavelength photonic jet in the photoresist. Because the illumination can be controlled over larger scales (several μm resolutions) using a conventional mask, the technique facilitates very low cost hierarchical patterning with sub-400 nm feature sizes. The paper demonstrates the fabrication of metasurfaces over 15 cm ² and are measured using FTIR and imaged with a thermal camera.