Study on (Ba,Ca)(Ti,Zr)O₃ dielectric cofired with copper electrode

In this study, the sintering temperature of a (Ba,Ca)(Ti,Zr)O₃ (BCTZ) dielectric for cofiring with a Cu inner electrode is determined to be lower than 1050 °C in a reducing atmosphere (N₂/H₂ = 95/5) by using the sintering aids SiO₂ and Li₂CO ₃. The contents of SiO₂ and Li₂CO₃ are studied to achieve optimum dielectric characteristics and microstructure. The BCTZ dielectric with 0.25 wt% SiO₂ and Li₂CO ₃ fired with a Cu electrode at 1050 °C for 2 h in a reducing atmosphere shows promising properties, such as a dielectric constant of up to 9500, a low dielectric loss of 23 × 10^-4,and a high insulation resistance of up to 1.2 × 10¹²Ω. However, the excess amount of Li₂CO₃ results from the formation of the secondary phase. Ithas been determined that the secondary phase is (Ba _1.55Ca_0.45SiO₄) by high-resolution transmission electron microscopy and energy-dispersive spectrometry (HRTEM-EDS). The presence of the secondary phase is harmful to the properties of the BCTZ dielectric including dielectric constant, insulation resistance, and degree of dielectric loss. The interdiffusion of the dielectric-electrode interface is observed in the backscattered electron imaging (BEI) and line scan modes. The result indicates that such interdiffusion is easier from the electrode to the dielectric layer than from the dielectric layer to the electrode.