Interdigitated Terahertz Metamaterial Sensors: Design with the Dielectric Perturbation Theory

• Lei Cao, Fanqi Meng, Esra Özdemir, Yannik Loth, Merle Richter, Anna Wigger, Maira Perez, Alaa Jumaah, Shihab Al-Daffaie, Peter Haring Bolivar, and Hartmut Roskos
• received 12/15/2023; accepted 03/04/2024; posted 03/04/2024; Doc. ID 516228
• Abstract: Designing terahertz sensors for highly sensitive detection of nanoscale thin films and a few biomolecules poses a substantial challenge, but is crucial for unlocking their full potential in scientific research and advanced applications. This work presents a strategy for optimizing metamaterial sensors in detecting small amounts of dielectric materials.The amount of frequency shift depends on intrinsic properties (electric field distribution, Q-factor, and mode volume) of the bare cavity, as well as the overlap volume of its high-electric-field zone(s) and the analyte. Guided by the simplified dielectric perturbation theory, interdigitated electric split-ring resonators (ID-eSRR) are devised to significantly enhance detection sensitivity compared to eSRRs without interdigitated fingers. ID-eSRR's fingers redistribute the electric field, creating strongly localized enhancements that boost analyte interaction. The periodic change of the inherent anti-phase electric field reduces radiation loss, leading to a higher Q-factor. Experiments with ID-eSRR sensors operating at around 300 GHz demonstrate a remarkable 33.5 GHz frequency shift upon depositing a 150 nm SiO2 layer as an analyte simulant, with a figure of merit (FOM) improvement of over 50 times compared to structures without interdigitated fingers. This rational design offers a promising avenue for highly sensitive detection of thin films and trace biomolecules.