ZnTiO3 ceramic sintered at low temperature with glass phase addition for LTCC applications

The compound ZnTiO3 is an attractive dielectric ceramic owing to its good dielectric properties at high frequency range (epsilon(Gamma) =21, tan(delta) < 10(-4), tau(f) congruent to -55 ppm/degrees C) and its relatively low sintering temperature (below 1200 degrees C). Nevertheless, it is well established that the synthesis of pure ZnTiO3 phase is very difficult since ZnTiO3 partially decomposes at high temperature into TiO2 and Zn2TiO4. Consequently, sintered specimens usually contain these secondary phases. Another point which needs to be underlined is the lowering of the sintering temperature in order to be compatible with silver co-sintering. For that, the addition of glass phases from the system ZnO-SiO2-B2O3 has been investigated. The effect of such additions on the dilatometric curves, the microstructure, the phase composition and the dielectric properties has been carefully examined. It was shown that the addition of 5 wt.% of (ZnO-B2O3) or (ZnO-SiO2-B2O3) allows sintering ZnTiO3 at 900 and 930 degrees C, respectively. In addition to the sintering temperature decreasing, it is-clearly evidenced that some glass phases addition allows to suppress the secondary phases after the sintering stage. For example, starting from a powder containing ZnTiO3 as majority phase and TiO2 + Zn3Ti2O8 as secondary phases, the addition of some glass phases allows getting a pure and dense ZnTiO3 ceramic after a sintering performed at 900 degrees C. Typical samples sintered in such conditions exhibit a density higher than 94% of the theoretical value, a relative permittivity epsilon(Gamma) = 21, a loss factor tan(delta) < 10(-3) and a temperature dependence of permittivity low with a value close to 30 ppm/degrees C. These properties make these compositions suitable for low temperature co-fired ceramics applications (LTCC). (C) 2007 Elsevier B.V. All rights reserved.