Low Sintering Temperature of CuO-Fluxed Ag(Nb, Ta)O_3 Dielectric Ceramics

摘要

Solid solutions in the Ag(Nb_xTa_(1-x))O_3 (where 0 ≤ x ≤ 1) system exhibit excellent dielectric properties at microwave frequency including high dielectric constant (200< k <400), low loss (tanδ ～ 0.004) and a composition controlled temperature coefficient of capacitance (TCC). For Ta-rich and Nb-rich solid solutions, the TCC values are negative and positive, respectively, and two-phase mixtures provided an average TCC close to zero. Series, parallel, and logarithmic mixing rules were applied to predict dielectric constant and TCC of polyphase assemblages (45wt%Ag(Nb_(0.65)Ta_(0.35))O_3+55wt% Ag(Nb_(0.35)Ta_(0.65))O_3) yielded an average dielectric constant of 450 and a TCC of 180ppm/℃. Microstructure analysis revealed that a CuO-rich liquid remains at the grain boundary and transmission electron microscopy shows that the CuO resides at triple points. Ag(Nb_xTa_(1-x))O_3 ceramics were successfully integrated into LTCC for embedded capacitors. The addition of CuO lowered the sintering temperature to below 900℃ and a low TCC was maintained for fine grained microstructures.