Increased frequency shifts in high aspect ratio terahertz split ring resonators

The resonance of split ring resonators (SRRs) is known to shift upon the addition of a dielectric overlayer, a feature useful for practical applications. Here, we demonstrate that the frequency shift is enlarged by increasing the SRR height, thereby potentially enhancing sensitivity and tunability. We fabricated SRRs resonating at terahertz frequencies using a focused proton beam. This resulted in SRRs nearly 10 μm high, with smooth and vertical sidewalls. Terahertz time domain spectroscopy was used for characterization. Upon applying a dielectric overlayer (ϵ=2.7), a resonance located at 640 GHz shifted by nearly 120 GHz. Simulations also indicate a widening frequency shift as SRR height increases.