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

In this study, we aimed to develop high permittivity TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> ceramics ideal for the fabrication of All-Dielectric Metamaterials operational in the terahertz frequency. TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> 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 ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ε^ 100</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tanδ < 0.015</tex> ). 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 <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> etching by Inductively Coupled Plasma.