Investigation of Resonant Properties of Metamaterial THz Modulators Fabricated from Vanadium Dioxide Thin Films

Abstract

The metal to insulator transition (MIT) in vanadium dioxide (VO2) has played a key role in development of devices in the terahertz frequency range. In the present study, the use of VO2 patterned as a metamaterial surface or coupled as a homogeneous layer with a metallic metamaterial surface on top is investigated in terms of performance. High quality VO2 thin films were deposited on c-cut sapphire substrates by using the dc magnetron sputtering technique. A change in resistivity by a factor of 104 MIT in VO2 was observed allowing to investigate its use as a controllable metamaterial. The layer was patterned using a unique geometry (four-cross shaped) that operates in the THz frequency range. To understand its performance as a tunable THz filter, the four-cross structure fabricated from VO2 is compared to one fabricated from Au on VO2 bare film using UV lithography and ion beam etching techniques. The spectral performances of metamaterials was assesed using THz-Time Domain Spectroscopy (THz-TDS) and results were compared with simulations based on CST Microwave Studio. Absence of the resonant effects in the purely developed VO2 device while clear observation of the MIT behavior shows the strong dependency of the inductive and/or capacitive effets of the four-cross structure on conductivity of the surface metamaterial which is clearly observable for the Au-based device. In the latter case, the resonant transmittance of the filter can be effectively modulated by change in temperature.