Synthesis, microstructure and characterization of ultra-low permittivity CuO–ZnO–B2O3–Li2O glass/Al2O3 composites for ULTCC application

In view of lead-free low-softening CuO–ZnO–B 2 O 3 –Li 2 O glass, novel glass/Al 2 O 3 ceramic composites were prepared by solid-state reaction route for ultra-low temperature co-fired ceramic (ULTCC) applications. The phase evolution and compositions, microstructure and microwave dielectric properties of the composites were studied by XRD , SEM and dielectric property measurement. Four phases including Cu 2 Al 6 B 4 O 17 , Li 2 CuB 4 O 8 , CuB 2 O 4 and Al 2 O 3 coexist in the glass/Al 2 O 3 ceramic composites sintered in the range of 640–660 °C. However, the contents and types of the phases depend on the composition of the composites and firing temperature. The optimum properties with a permittivity ε r  = 3.79, a quality factor Q ×  f  = 38557 GHz (at 16.64 GHz) and a temperature coefficient of resonance frequency τ f ≈0 ppm/ o C as well as a heat conductivity λ = 1.46W(mK) −1 can be achieved for the glass/ceramic composite containing 10 wt% Al 2 O 3 sintered at 640 °C. Moreover, the composite can be co-fired compatible with Ag and Al electrodes.The as-prepared glass/Al 2 O 3 ceramic composites are promising candidate for ULTCC application.