Low loss photopatternable matrix materials for LWIR-metamaterial applications

Transparent matrix materials with low-loss and low-permittivity are an important component of integrated optical devices including filters, lenses, and novel metamaterials. Many of the structural matrix materials that are currently utilized at visible and near-infrared wavelengths, such as solution deposited, high-k dielectrics and commercial photoresists, exhibit vibrational absorption bands in the 8–12 μm spectral range which represents a significant challenge to developing transmissive, three-dimensional (3D) metamaterials operating in the long wavelength infrared (LWIR) spectral region. In this paper, we present new, low loss photopatternable polymer dielectrics as well-suited matrix materials for fabricating LWIR-metamaterials. These materials are synthesized by partially hydrogenating polynorbornene to varying degrees followed by a thiol-ene coupling reaction to cross-link the remaining olefin groups. After cross-linking, the olefin LWIR-absorption band is minimized and the glass transition temperature (Tg) of the material increases. Thick layers of the polymer (>3 μm), which acts as a negative photoresist, can be deposited easily using a spin coating technique to develop planarizing layers with photopatternable vias. A demonstration on the low loss nature of the polymer dielectrics was carried out by incorporating the polymer into an all-dielectric, infrared metamaterial. Thus, the material is ideal for both lithography and fabrication of 3D metamaterial structures operating in the LWIR spectral region.