From Bulk Toward Micro-Structured TiO2 Ceramics for All-Dielectric Metamaterials at Terahertz Frequencies

In this study, we aimed to develop high permittivity TiO 2 ceramics ideal for the fabrication of All-Dielectric Metamaterials operational in the terahertz frequency. TiO 2 ceramic pellets are fabricated from a commercial powder. A comparative analysis was conducted between Spark Plasma Sintering (SPS) and conventional sintering process. Characterizations were then carried out in the range of 0.2 to 1.4 THz using THz time-domain spectroscopy. We observed that the samples fabricated by the spark plasma sintering and post-annealing treatment exhibit a high refractive permittivity associated with minimal loss ( $\epsilon^{\prime} \simeq \mathbf{100}$ and $\tan\delta < \mathbf{0.015}$ ). These characteristics make these samples optimal candidates for achieving a negative refractive index in all-dielectric metamaterials. In addition, two micro-structuring processes were investigated for the realization of metamaterials operating in the terahertz range: (i) micro-molding and (ii) direct TiO 2 etching by Inductively Coupled Plasma.