Low-temperature sintering and microwave dielectric properties of CaWO4 ceramics for LTCC applications

Microwave dielectric properties of CaWO4 ceramics were investigated as a function of H3BO3 and/or Bi2O3 content and sintering temperature. For a single addition of H3BO3 (1 <= x (wt.%) <= 5), the density of specimen increased up to 3 wt.% H3BO3, and then decreased. The dielectric constant (K) and the quality factor (Q x f) of the specimens sintered at 850 degrees C showed lower value than those of specimens sintered above 900 degrees C due to the poor sinterability. With the increase of H3BO3 content of 0.5 wt.% Bi2O3-yH(3)BO(3) (5 <= y (wt.%) <= 20), the sintering temperature of CaWO4 ceramics could be effectively reduced from 1100 to 850 degrees C without degradation of dielectric properties. For the specimens sintered at 850 degrees C for 30 min, K was not changed remarkably with Bi2O3-H3BO3 Content; however, Q x f value increased up to 9 wt.% 1431303 of 0.5 wt.% Bi2O3-yH(3)BO(3), and then decreased. The temperature coefficient of resonant frequency (TCF) shifted to the positive value with increasing Bi2O3-H3BO3 content. Typically, K of 8.7, Q x f of 70,220 GHz and TCF of -15 ppm/degrees C were obtained for the specimens with 0.5 wt.% Bi2O3-9 wt.% H3BO3 sintered at 850 degrees C for 30 min. (c) 2005 Elsevier Ltd. All rights reserved.