Terahertz band-pass filters based on fishnet metamaterials fabricated on free-standing SiNx membrane

Terahertz (THz) band-pass filters constructed by metal-SiNx-metal hollow fishnet metamaterials were designed and fabricated. Results reveal that the as-fabricated single-layer filter responds at 3.75 THz with a high transmission of 88.1% and broad full width at half maximum of 2.79 THz. For such filters, a free-standing SiNx membrane is utilized specially as both dielectric and supporting materials, by which the insertion loss widely existed in those filters fabricated on rigid substrates can be efficiently avoided. Moreover, the critical parameters for determining the responses of the filters were systematically investigated. In our approach, multi-layer filters can be easily fabricated just by stacking the metamaterials layer by layer, and thus the spectral transmission, bandwidth, and out-of-band rejection can be rationally adjusted. This work describes a promising approach to design and fabricate THz band-pass filters based on substrate-free fishnet metamaterials.