Synthesis of porous dielectric materials for future wireless high frequency applications

In future, high frequency applications and devices need to be able to cope with ultra-reliable and extremely low-latency data transmission, thus dielectrics of substrates and other structural components are expected to have low relative permittivity and loss factor to ensure the ideal propagation of electromagnetic waves; this may be achieved by introducing pores into the material. In the present work, various porous silica-based dielectric materials and composites with excellent electromagnetic properties at millimeter wave frequency bands and beyond have been developed. First, a porous composite of silica nanoshells and cellulose nanofibers was made having permittivity and loss factor of 1.19 and 0.01 at 300 GHz, respectively. Next, to achieve even better electromagnetic performance, a nanocellulose film-enveloped silica foam was synthetized with a porosity of 98.9%, resulting in extremely low permittivity and loss factor (1.02 and 0.0003, respectively at 300 GHz). The feasibility of the two silica-cellulose-based materials for high frequency applications was demonstrated by sputtering thin metal film patterns on their surfaces for filter and lens applications operating at 300 GHz. The synthetized dielectrics are suitable candidates for devices operating at higher frequencies, according to their electromagnetic properties, measured up to 2 THz. Finally, our research was focusing on porous dielectric materials which had higher mechanical strength; therefore, porous composites of silica nanoshells and poly(methyl methacrylate) were synthetized, having dielectric permittivity and loss factor of 1.51 and 0.004, respectively, at 200 GHz. Capitalizing on the thermoplastic behavior of the composite, it was processed further by hot pressing in a mold to produce a bullet shaped refractive lens, with operating frequency at around 140 GHz. The results presented in this thesis show a great potential of porous silica materials as dielectric substrates for future high frequency devices. Although the developed ...