From bulk toward micro-structured TiO₂ ceramics for all-dielectric metamaterials at terahertz frequencies: what process?

In this study, we aimed to develop high permittivity TiO₂ ceramics ideal for the fabrication of all-dielectric metamaterials (ADM) operational in the terahertz frequency. TiO₂ ceramic pellets have been 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 0.2–1.4 THz using THz time-domain spectroscopy. We observed that the samples fabricated by the SPS and post-annealing treatment exhibit a high permittivity associated with minimal loss ( ε 100 and tanδ < 0.015). These characteristics make these samples optimal candidates for achieving a negative or near-zero effective index in all-dielectric metamaterials. In addition, four micro-structuring processes were investigated to produce ADM operating in the terahertz range from the ceramics: (i) micro-molding, (ii) direct TiO₂ etching by inductively coupled plasma, (iii) saw cutting and (iv) femtosecond laser etching.