Effect of CuO and TiO₂ on the sintering temperature and dielectric properties of BaWO₄ for LTCC applications

A series of (1-x) BaWO₄-xCuO low-temperature sintered composite ceramics were prepared via co-firing the mixture of BaWO₄ and CuO in the first part of this study. The sintering temperature of BaWO₄ was decreased from 1150 °C to 950 °C when a little amount of CuO was used as sintering aids. The 0.95BaWO₄-0.05CuO sample heated at 950 °C for 4 h had good dielectric performance (Q × f ~ 31,847 GHz, ε_r ~ 7.99, τ_f ~ −81.7 ppm/°C). However, the negative τ_f was too large to apply to practice. To solve this problem, the rutile phase TiO₂ nano-particle with a large positive temperature coefficient of +450 ppm/°C was added as τ_f compensator in the second part of the study. TiO₂ powders not merely improved the temperature stability, but promoted the grain growth. However, the ε_r value increased from 10.5 to 12.6 and Q×f value decreased slightly as TiO₂ content increased from 0.30 to 0.45. The 0.65 (0.95BaWO₄-0.05CuO) −0.35TiO₂ composite ceramic displayed an optimum performance (Q × f ~ 22,012 GHz, ε_r ~ 11.21, τ_f ~ −2.9 ppm/°C). Such a sample was chemically compatible with silver, implying that it can be implemented on LTCC applications.