Low temperature sintering and microwave dielectric properties of CaSiO3–Al2O3 ceramics for LTCC applications

The effects of CuO, Li2CO3 and CaTiO3 additives on the densification, microstructure and microwave dielectric properties of CaSiO3–1 wt% Al2O3 ceramics for low-temperature co-fired applications were investigated. With a single addition of 1 wt% Li2CO3, the CaSiO3–1 wt% Al2O3 ceramic required a temperature of at least 975 °C to be dense enough. Large amount addition of Li2CO3 into the CaSiO3–1 wt% Al2O3 ceramics led to the visible presence of Li2Ca3Si6O16 and Li2Ca4Si4O13 second phases. Fixing the Li2CO3 content at 1 wt%, a small amount of CuO addition significantly promoted the sintering process and lowered the densification temperature to 900 °C whereas its addition deteriorated the microwave dielectric properties of CaSiO3–1 wt% Al2O3 ceramics. Based on 10 wt% CaTiO3 compensation in temperature coefficient, good microwave dielectric properties of εr=8.92, Q×f=19,763 GHz and τf=−1.22 ppm/°C could be obtained for the 0.2 wt% CuO and 1.5 wt% Li2CO3 doped CaSiO3–1 wt% Al2O3 ceramics sintered at 900 °C. The chemical compatibility of the above ceramics with silver during the cofiring process has also been investigated, and the result showed that there was no chemical reaction between silver and ceramics, indicating that the as-prepared composite ceramics were suitable for low-temperature co-fired ceramics applications.