Low-temperature sintering and microwave dielectric properties of B2O3-added ZnO-deficient Zn2GeO4 ceramics for advanced substrate application

Abstract

ZnO-deficient Zn2-xGeO4-x ceramics with 0.05 <= x <= 0.15 were synthesized because a ZnO secondary phase is formed in the stoichiometric Zn2GeO4 ceramics synthesized using micrometer-sized ZnO and GeO2 powders. The Zn1.3GeO3.9 ceramic sintered at 1000 degrees C showed a homogeneous Zn2GeO4 phase with good microwave dielectric properties: epsilon(r) of 6.8, Q x f of 49,000 GHz, and tau(f) of -16.7 ppm/degrees C. However, its sintering temperature was still too high for it to be used as an advanced substrate for low-temperature co-fired ceramic devices. Therefore, various amounts of B2O3 were added to the Zn1.9GeO3.9 ceramics to reduce their sintering temperature. Owing to the formation of a B2O3-GeO2 liquid phase, these ceramics were well sintered at low temperatures between 925 degrees C and 950 degrees C. In particular, 15 mol% B2O3-added Zn1.9GeO3.9 ceramic sintered at 950 degrees C showed promising microwave dielectric properties for advanced substrates without the reaction with an Ag electrode: epsilon(r) = 6.9, Q x f = 79,000 GHz, and tau(f) = 15 ppm/degrees C.