Low‐Temperature Synthesis and Growth of Bulk Ba ₂ Ti ₉ O ₂₀ Ceramics on Conducting Substrates for Applications in Integrated Dielectric Resonator Devices

This paper describes the synthesis of Ba ₂ Ti ₉ O ₂₀ ceramics at extremely low temperatures (∼150°C) and the subsequent growth of bulk resonators on silicon substrates by hydrothermal processing of their sol–gel composites. X‐ray diffraction analysis shows excellent crystallinity, while scanning electron microscopy evidenced densification and development of bridging structures at the grain boundaries and interfaces. Transmission electron micrographs further confirmed the development of sol–gel‐derived crystalline interfaces between sol–gel‐derived material and powder particles. The dielectric properties of a resonator measured in the 5–6 GHz microwave frequency range were ɛ _r =38 and Q _u × f =12,000 at 5.6 GHz and τ _f =+6 ppm/°C. The density, dielectric properties, and mechanical strength at the bulk ceramic–thin film interface are enhanced by a hydrothermally induced dissolution–crystallization process, which leads to interparticle bridges. The novel low‐temperature ceramic process has high potential for the growth of ceramic resonators on integrated circuits and is demonstrated by the fabrication of an integrated dielectric resonator antenna for system‐on‐chip applications.