Low-Temperature Sintering of Gahnite Ceramic Using Cu-Nb-O Additive and Evaluation of Dielectric and Thermal Properties

Abstract

Low-temperature sintering of gahnite (ZnAl2O4) ceramic, which has the potential to exhibit higher thermal conductivity than alumina but sinters densely at a moderate temperature of approximately 1500°C, has been investigated. When adding only 5 wt.% Cu-Nb-O additive, the sintering temperature was lowered significantly to 960°C. The sample fired at 960°C for 2 h exhibited a relative permittivity (er) of 9.1, a quality factor multiplied by resonant frequency (Q × f) value of 30,000 GHz (at a measurement frequency of approximately 13 GHz), and a temperature coefficient of resonant frequency (τf) of −69 ppm/K, being relatively satisfactory values. However, the thermal conductivity of the sample was 9.3 W/m-K, which exceeds that of conventional low-temperature co-fired ceramic (LTCC) materials but is only one-third of that of the pure gahnite sample (27 W/m-K). Our analysis revealed that the main cause was the incorporation of the Cu component into the gahnite lattice. These results enable the proposal of guidelines for the development of new LTCC materials with high thermal conductivity.