ZnTiO 3 ceramic sintered at low temperature with glass phase addition for LTCC applications

Abstract

The compound ZnTiO 3 is an attractive dielectric ceramic owing to its good dielectric properties at high frequency range ( ɛ r = 21, tan( δ) < 10 −4, τ f ≅ −55 ppm/°C) and its relatively low sintering temperature (below 1200 °C). Nevertheless, it is well established that the synthesis of pure ZnTiO 3 phase is very difficult since ZnTiO 3 partially decomposes at high temperature into TiO 2 and Zn 2TiO 4. 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–SiO 2–B 2O 3 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–B 2O 3) or (ZnO–SiO 2–B 2O 3) allows sintering ZnTiO 3 at 900 and 930 °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 ZnTiO 3 as majority phase and TiO 2 + Zn 3Ti 2O 8 as secondary phases, the addition of some glass phases allows getting a pure and dense ZnTiO 3 ceramic after a sintering performed at 900 °C. Typical samples sintered in such conditions exhibit a density higher than 94% of the theoretical value, a relative permittivity ɛ r = 21, a loss factor tan( δ) < 10 −3 and a temperature dependence of permittivity low with a value close to 30 ppm/°C. These properties make these compositions suitable for low temperature co-fired ceramics applications (LTCC).