  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.
