Hyperbolic metamaterials based on multilayer Ag/TiNxOy structure for SPR refractive index sensors

Plasmonic sensors based on hyperbolic metamaterials (HMMs) have excellent development prospects because of their high sensitivity, low cost, and applicability towards label-free detection of single molecules. Here, we designed HMMs based on alternating thin films structure of the traditional silver plasma material and prepared a TiNxOy material. The real dielectric constant of TiNxOy was made positive by introducing O into TiN, which was used as the dielectric component of the hyperbolic metamaterial. We performed finite-difference time-domain simulations to explore the optimal number of layers of Ag/TiNxOy HMMs. We then used magnetron sputtering to prepare an Ag/TiNxOy HMM device, which yielded hyperbolic dispersion after 608 nm. Additional plasmon resonance test results demonstrated that the HMM device has an excellent response to refractive index changes in the near-infrared band, making it suitable for plasmonic refractive index sensing. The plasmonic sensor designed in this work is suitable as a low-cost and highly sensitive biosensor in the near-infrared band.