Solid-State-Activated Sintering of ZnAlO Ceramics Containing CuNbO with Superior Dielectric and Thermal Properties.

Low-temperature co-fired ceramics (LTCCs) are dielectric materials that can be co-fired with Ag or Cu; however, conventional LTCC materials are mostly poorly thermally conductive, which is problematic and requires improvement. We focused on ZnAlO (gahnite) as a base material. With its high thermal conductivity (~59 W·m·K reported for 0.83ZnAlO-0.17TiO), ZnAlO is potentially more thermally conductive than AlO (alumina); however, it sinters densely at a moderate temperature (~1500 °C). The addition of only 4 wt.% of CuNbO significantly lowered the sintering temperature of ZnAlO to 910 °C, which is lower than the melting point of silver (961 °C). The sample fired at 960 °C for 384 h exhibited a relative permittivity () of 9.2, a quality factor by resonant frequency ( × ) value of 105,000 GHz, and a temperature coefficient of the resonant frequency () of -56 ppm·K. The sample exhibited a thermal conductivity of 10.1 W·m·K, which exceeds that of conventional LTCCs (~2-7 W·m·K); hence, it is a superior LTCC candidate. In addition, a mixed powder of the CuNbO additive and ZnAlO has a melting temperature that is not significantly different from that (~970 °C) of the pristine CuNbO additive. The sample appears to densify in the solid state through a solid-state-activated sintering mechanism.