Novel Al2Mo3O12-based temperature-stable microwave dielectric ceramics for LTCC applications

Abstract

Microwave dielectric ceramics are key materials in low-temperature co-fired ceramic (LTCC) technology. In many material systems, Mo-based microwave dielectric ceramics have attracted world-wide attention in recent years due to their low intrinsic sintering temperature and high quality factor (Q × f). In combination with its low dielectric constant (ε_r), Al₂Mo₃O₁₂ is a very promising LTCC candidate, but the very negative temperature coefficient of its resonant frequency (τ_f) limits its application. In this work, novel (1 − x)Al₂Mo₃O₁₂–xTiO₂ (x = 0–0.4) microwave dielectric ceramics were designed and prepared by a conventional solid-state reaction. The effects of TiO₂ addition on the phase composition, microstructure, and microwave dielectric properties of the obtained Al₂Mo₃O₁₂-based ceramics were investigated. It was revealed that rutile TiO₂ could co-exist with monoclinic Al₂Mo₃O₁₂ in the samples after they were prepared under optimized conditions. With increasing addition of TiO₂, the ε_r value of the obtained ceramics increased from 5.69 to 6.85, the value of Q × f decreased from 73 910 to 45 720 GHz, and τ_f varied from −32.3 to +9.2 ppm °C⁻¹. When x = 0.3, microwave dielectric ceramics of near-zero τ_f (ε_r = 6.23, Q × f = 51 630 GHz, and τ_f = −3.3 ppm °C⁻¹) could be obtained. Such high-performance microwave dielectric ceramics would be promising for LTCC applications.