Twofold Plasmonic Resonator Based on Polyethylene Terephthalate Thin Films for Terahertz Sensing Applications

We demonstrate a chip-scaled reversible terahertz (THz) resonator in which bending the flexible substrate outward breaks a diabolo array into a bowtie array. The resonance frequency shifts from 0.5 THz to nearly twofold (∼1.1 THz) as the resonator bends outward. Tunable THz spectroscopy achieved by mechanical bending is explained by theoretical simulation. For the cases of flattening/bending/reflattening, we analyze electrical current–voltage characteristic and optical properties in THz transmission spectra. While the current–voltage curves subsequently exhibit metal-, capacitor-, and tunneling-like results, THz transmittance shows twofold resonant behavior. In this behavior, we further demonstrated molecular sensing two materials, α-lactose and caffeine, on a single resonator. Considering the volume of the gap region, the detection limit of the molecules within the gap region for the bowtie antenna array is 80.5 and 64.4 pg for lactose and caffeine, respectively. The detection limit is determined by terahertz transmission change (ΔT/T0) and resonance frequency shift (Δf/fres) caused by the molecules within the gap region due to terahertz field confinement. We expect that this approach provides a more stable and functional platform for THz sensing applications.