Phase evolution and dielectric properties of La2O3–B2O3–ZnO glass-ceramics/Al2O3 composites for LTCC substrates at high frequencies

Low-temperature sinterable and low-loss composites consisting of La2O3–B2O3–ZnO glass-ceramics and Al2O3 filler have been investigated. The phase composition of LBZ/Al2O3 composites is closely related to the sintering temperature. When the sintering temperature was 850 °C, the main phases included LaBO3 and La(BO2)3 precipitated from LBZ glass-ceramics, ZnAl2O4 and LaAl2.03(B4O10)O0.54 phases generated by interfacial reactions, and Al2O3 filler. The high content of crystalline phases in the composites indicated the low content of residual glassy phases, which was related to the low loss of the composites at high frequencies, especially at microwave frequencies. The initial sintering temperature and the temperature corresponding to the fastest shrinkage speed of LBZ/40A and LBZ/50A composites were related to the content of LBZ glass-ceramics, and all the composites could be densified at low temperatures. Optimum properties were exhibited for the composite of LBZ glass-ceramic with 50 wt% Al2O3 sintered at 900 °C with a permittivity εr = 7.3 and a dielectric loss tan δ = 1.62 × 10−3 (at 12.1 GHz). The low εr and tanδ coupled with a low sintering temperature, suggesting that the LBZ glass-ceramic/Al2O3 composites had potential to meet the requirements of LTCC substrate materials for high frequencies.