Impact of sintering conditions on the dielectric properties of TiO2 ceramics for metamaterialsapplications at terahertz frequencies
Titanium dioxyde (TiO2) is a promising dielectric material for the realization of metamaterials operating in the terahertz (THz) range. Indeed, these necessitate a high permittivity and low loss material. In this paper, we compare the processes of fabrication and the results of characterisation of bulk TiO2 pellets. From the results of this characterization, we have numerically designed 2D all dielectric metamaterials (ADM) showing that they may exhibit negative or near-zero effective index. Our previous simulations show that the relative permittivity epsilon has to be around 100, while the loss tangent has to be lower than 0.02. We have thus compared conventional sintering (CS) vs spark plasma sintering (SPS), and investigated the effect of post-sintering annealing on the loss to satisfy these two criteria. The samples were characterized by THz Time Domain Spectroscopy (THz-TDS). One of the samples exhibits a loss tangent as low as 0.006, with a permittivity epsilon = 103. These results highlight the importance of the fabrication process on the EM properties of bulk TiO2, and demonstrate that it is a promising material for the development of metamaterial in the THz band.