Fine Grained Relaxor Dielectric Ceramics Prepared by Hydrothermally Synthesized Powder

In response to the demand for small grain size in thin dielectric layers of multilayer capacitors (MLCs), relaxor dielectric powder was hydrothermally synthesized. The sintering temperature for the hydrothermally synthesized powder was reduced to 950° C from 1200° C for the conventional solid phase reaction synthesized powder. As a result, the grain size of sintered specimens decreased from 3.9 µm for the solid phase reaction synthesized powder as a starting powder to 1.3 µm for hydrothermally synthesized powder: this is equivalent to the smallest grain size of a commercially available X7R-designated barium titanate-based dielectric fired at 1300° C. Using the hydrothermally synthesized powder, Y7R-designated 7.4 µF MLCs with 3.2 µm-thick 240 dielectric layers of EIA1206 size (3.2×1.6×1.5 mm) were fabricated. The MLCs were fired at 1000° C for 2 h and the grain size was 1.3 µm. The capacitance per unit volume of these MLCs is approximately 900 µF/cm³, which is comparable with that for tantalum capacitors. In addition, the new MLCs have a low dissipation factor of 1.3% and stable dependence of capacitance on dc bias voltage as compared with BaTiO₃-based MLCs.