Silicate dielectric ceramics for millimetre wave applications

Abstract

Silicate ceramics are of considerable promise as high frequency dielectrics in emerging millimetre wave applications including high bandwidth wireless communication and sensing. In this review, we show how high quality factors and low, thermally stable permittivities arise in ordered silicate structures. On the basis of a large number of existing studies, the dielectric performance of silicate ceramics is comprehensively summarised and presented, showing how microstructure and SiO4 tetrahedral connectivity affect polarizability and dielectric losses. We critically examine the appropriateness of silicate materials in future applications as effective millimetre wave dielectrics with low losses and tuneable permittivities. The development of new soft chemistry based processing routes for silicate dielectric ceramics is identified as being instrumental towards the reduction of processing temperatures, thus enabling silicate ceramics to be co-fired in the production of components functioning in the mm wave regime.

A comparison of syntheses approaches towards functional polycrystalline silicate ceramics

“…Prominent examples of ionic replacements for the tuning of material parameters are found in almost every materials science direction. In the ongoing search for materials with ever improved dielectric properties for high frequency wireless applications, cation substitutions are often introduced in the host material to reduce dielectric loss [49][50][51], achieve near zero temperature factor of resonant frequency [52,53], reduce secondary phase formation [54], improve densification and adjust its permittivity [1]. Bioactive glasses and ceramics are routinely substituted with a broad range of cations to harness their profound effects on the material properties.…”

“…Silicate ceramics are of emerging relevance as functional materials in a broad range of applications. Numerous crystalline silicate phases of neso-, soro-, ino-, cyclo-and tectosilicates, differentiated by linking of SiO 4 tetrahedra, have been found in recent years to exhibit promising characteristics towards applications as high-frequency dielectrics [1], bioactive ceramics [2,3], battery electrodes [4] and tritium breeders [5][6][7][8]. Silicates are promising multifunctional materials, whose utilisation hinges on our ability to fabricate such materials in controllable and appropriate forms and stoichiometries.…”

“…Extensive substitutions are commonly possible at octahedral cation sites in silicates of all families. Many such substitutions are known from the world of geosciences, and when introduced in controlled quantities in the context of ceramics processing, can be used to tune the physical and chemical behaviour of applied silicates [1]. Substitutions at tetrahedral Si sites with other cations such as Al could offer further pathways for materials design.…”

High‐strength ceramic foams with ultralow dielectric constant and loss in terahertz frequency region

“…Although dense polymers exhibit a relatively low ε r (2 < ε r < 4), they usually have a high tan δ 3 . Conversely, dense microwave dielectric ceramics exhibit a relatively high ε r (3 < ε r < 120) and moderate tan δ 4,5 . As reported, microwave dielectric ceramics are widely used in the fabrication of microwave devices such as antennas, filters, and resonators, 4,6,7 and some of them have excellent dielectric properties in terahertz frequency range 8–10 .…”

Sintering behavior and microwave dielectric properties of CaTi1-x(Nb1/2Al1/2)xO3

“…Dielectric ceramics are widely used in different communication systems such as cellular phones, satellites, base stations, military radar, navigation system, ITS, automation, filters, oscillators etc. For microwave (MW) applications, appropriate relative permittivity (εr), low tan δ or high Q×fo and near zero temperature coefficient of resonance frequency (τf) are preferred [1][2][3]. For MW applications, perovskites are of special interest due to their interesting physical and chemical properties.…”