Fabrication and application of 3D Terahertz metamaterials with vertical multinanogaps for spectroscopic sensing

Terahertz (THz) metamaterials have garnered attention for their unique electromagnetic properties and potential applications in biomaterial sensing, offering label-free, non-contact capabilities. However, their performance is limited by their diffraction limits, impeding the detection of small objects. This study presents an approach for fabricating three-dimensional (3D) THz metamaterials with vertically oriented, high-aspect-ratio multinanogaps. These 3D metamaterials comprise laminated cross-shaped metal layers, which induce electromagnetic resonance, and polymer layers that support the metal layers at the center of the cross shape. Air nanogaps formed between metal layers achieved aspect ratios of > 64. Conventional microfabrication techniques were employed, including spin coating, metal sputtering deposition, photolithography, ion milling etching, and oxygen plasma etching, without relying on electron beam lithography. Spectroscopic analyses of the fabricated metamaterials revealed that the multilayered structure exhibited a deeper dip than single-layered and double-layered configurations. To validate THz sensing, we used isopropyl alcohol (IPA) for THz spectroscopy applications; the spectra indicated significant peak frequency shifts in the transmission dip of the fabricated device with and without IPA. These findings highlight the application scope of the as-prepared 3D THz metamaterial in material sensing techniques, enhancing THz-metamaterial-based device performance.