Spectral properties of thick split ring resonators in the THz regime

Abstract

We fabricated and studied a planar composite material consisting of sub-wavelength double split ring resonator structures made of Gold on a Silicon substrate. Our measurements reveal a strong transmission dip at 0.6 THz. Experimental and numerical results indicate that there is an Inductor-Capacitor resonance at 0.6 THz, characterized by enhanced electric field strength across the ring gap. Our results also indicate a shift in the resonance to higher frequencies as thickness is increased. Spectral properties of the composite material were measured using THz Time Domain Spectroscopy in the range from 0.1 THz to 3.5 THz. Simulations were carried out using the commercially available electromagnetic solver, Microwave StudioTM. Fabrication of the structures was done with Proton Beam Writing, a nanolithography technique based on focused MeV protons. The direct-write technique allowed us to fabricate structures much thicker than otherwise possible. For this work, the ring resonator structures had overall dimensions of 38 μm and a thickness of 8 μm with highly vertical and smooth sidewalls with minimum critical dimensions of 2 μm.