Improvement in the temperature stability of a BaTiO₃-based multilayer ceramic capacitor by constrained sintering

In this study, a self-constrained BaTiO₃ material system, composed of a low-fire BaTiO₃-based X7R (ΔC/C±15% within -55° to 125°C) MLCC dielectric and a high-fire, BaTiO₃-based X7R MLCC dielectrics eliminated sintering aid that are laminated on both sides of the BaTiO₃-based X7R MLCC, has been developed. The temperature dependence of capacitance of the BaTiO₃-based X7R MLCC is significantly improved to satisfy X8R requirements over the entire temperature range studied (ΔC/C±15% within -55° to 150°C) using the self-constrained sintering. The curie temperature of BaTiO₃-based X7R MLCC increases on increasing the thickness of the constraining layers. Compared with the specimen fired by free sintering, a substantial reduction in grain size, leading to a decrease in dielectric constant, was observed in the specimen fired by constrained sintering with the thickness of the constraining layer being 170 μm. The increase in Curie temperature and decrease in grain size of the specimen fired by constrained sintering can be explained in terms of the presence of in-plane tensile stress. The in-plane tensile stress that introduces a friction force between the multilayer matrix and the nonshrinkage constraining layers to suppress the in-plane shrinkage and to inhibit the rate of grain growth was formed during constrained sintering.