Interdigitated Terahertz Metamaterial Sensors: Design with the Dielectric Perturbation Theory

TL;DR

This paper introduces a novel interdigitated metamaterial sensor design based on dielectric perturbation theory, significantly enhancing terahertz detection sensitivity for nanoscale thin films and biomolecules.

Contribution

The work presents a new interdigitated electric split-ring resonator design that improves sensitivity and Q-factor for terahertz sensors, validated through experiments at 300 GHz.

Findings

Frequency shift of 33.5 GHz with 150 nm SiO2 layer

FOM increases over 50 times compared to non-interdigitated structures

Enhanced electric field localization boosts analyte interaction

Abstract

Designing terahertz sensors with high sensitivity to detect nanoscale thin films and single biomolecule presents a significant challenge, and addressing these obstacles is crucial for unlocking their full potential in scientific research and advanced applications. This work presents a strategy for the design optimization of metamaterial sensors employed in the detection of small amounts of dielectric materials. The sensors usually utilize the shift of the resonance frequency as an indicator of the presence of the analyte. The amount of shifting depends on intrinsic properties (electric field distribution, quality 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 the detection sensitivity for thin-film analytes compared to eSRRs without interdigitated fingers in the SRR gap region. The fingers of the ID-eSRR metamaterial sensor redistribute the electric field, creating strongly localized field enhancements that substantially boost the interaction with the analyte. Additionally, the periodic change of the orientation of the inherent anti-phase electric field in the interdigitated structure reduces radiation loss, leading to a higher Q-factor. Experiments with e-beam-fabricated ID-eSRR sensors operating at around 300 GHz demonstrate a remarkable frequency shift of 33.5 GHz upon deposition of a SiO2 layer with a thickness of 150 nm as an analyte simulant. The figure of merit (FOM) improves by over 50 times compared to structures without interdigitated fingers. This rational design option opens a promising avenue for highly sensitive detection of thin films and trace biomolecules.