Broadband infrared metamaterial absorber with visible transparency using ITO as ground plane

Metamaterials that have broadband absorption at MIR frequencies, and yet, are transmitive at visible frequencies are fabricated using a semi-conducting Indium Tin Oxide (ITO) film as ground plane. The metamaterial absorber consists of an array of uniform aluminum disks separated by a Zinc Sulphide (ZnS) dielectric spacer layer from the ITO ground plane. The metamaterial was fabricated by a simple, cost-effective vapor deposition through a shadow mask. Compared with the usual metal/dielectric/metal tri-layer absorbers, the metal/dielectric/ITO absorber shows a peak absorbance of 98% and >70% over the mid-infrared regime from 4 to 7 μm. The broadband nature arises due to smaller dispersion in the dielectric permittivity of ITO compared to that of plasmonic metals at mid-infrared frequencies.