Isotropic metamaterial perfect light absorber using 3D split ring resonator in the mid IR region

We present the design of a perfect light absorber using 3D metamaterial for operation in the mid IR region. The 3D metamaterial is a metal half ring projecting normal to the substrate plane, which ensures wide-angle operation for the direct magnetic coupling. The absorber is essentially a 3-layer architecture having the 3D metamaterial on top acting as impedance matching layer to the surrounding medium, which ensures near zero reflection. A ground metal plane of 120nm thickness at the bottom layer cancels any transmission through the structure for incident electromagnetic field. A dielectric spacer layer of thickness 100nm separates the top and bottom layers. The metal parts of the absorber are realized using gold and the dielectric spacer layer is defined by SiN thin film deposited using PECVD. The 3D half rings are formed from the lithographically defined 2D template by releasing residual stress in the thermally evaporated gold thin film using ICP RIE of SiN sacrificial layer. We report an absorbance of more than 90% at a peak wavelength of 12.5 mu m with a FWHM of 2 mu m.