Ultra-porous alumina for microwave planar antennas

• Published in: Advanced Device Materials 2015-10, Vol.1 (4), p.93-99
• Main Authors: Stepanenko, O., Tartari, A., Amamra, M., Nguyen, T. H. N., Piat, M., Favero, I., Ducci, S., Khodan, A., Boinovich, L. B., Emelyanenko, A. M., Kanaev, A., Leo, G.
• Format: Article
• Language: English
• Subjects: Alumina; Aluminum oxide; Antennas; Chemical treatment; Cosmic microwave background; Dielectric loss; Microwaves; Morphology; Nanofibers; Oxidation; Oxides; Planar antennas; Porosity; Refractivity; Substrates; Ultra-porous alumina
• ISSN: 2055-0308; 2055-0316
• DOI: 10.1080/20550308.2015.1120442

We report on the experimental study of ultra-porous alumina (UPA) of transition phases γ and θ, which we fabricate by oxidation of laminated metallic aluminum followed by chemical and thermal treatments. Its morphology of a nanostructured monolith with up to 99% porosity brings together several crucial advantages with respect to existing aluminum oxides: an ultra-low density, the potential of refractive index gradients, and a chemically tunable hydrophilic character. Its extremely low permittivity measured here for the first time, ε r  ≈ 1.2 at 130-165 GHz, makes UPA a promising substrate material for planar electromagnetic components in this microwave spectral range of great interest for the cosmic microwave background observation. The dielectric loss tan δ ≈ 10 −3 , although being relatively low, can be further reduced after a chemical treatment that conveys hydrophobic character to the UPA constituting nanofibers.