FINE-GRAINED RELAXOR DIELECTRIC CERAMICS PREPARED BY HYDROTHERMALLY SYNTHESIZED POWDER

In response to the demand for small grain size in thin dielectric laye rs of multilayer capacitors (MLCs), relaxor dielectric powder was hydr othermally synthesized. The sintering temperature for the hydrothermal ly synthesized powder was reduced to 950 degrees C from 1200 degrees C for the conventional solid phase reaction synthesized powder, As a re sult, the grain size of sintered specimens decreased from 3.9 mu m for the solid phase reaction synthesized powder as a starting powder to 1 .3 mu m for hydrothermally synthesized powder this is equivalent to th e smallest grain size of a commercially available X7R-designated bariu m titanate-based dielectric fired at 1300 degrees C. Using the hydroth ermally synthesized powder, Y7R-designated 7.4 mu F MLCs with 3.2 mu m -thick 240 dielectric layers of EIA1206 size (3.2x1.6x1.5 mm) were fab ricated. The MLCs were fired at 1000 degrees C for 2 h and the grain s ize was 1.3 mu m. The capacitance per unit volume of these MLCs is app roximately 900 mu F/cm(3), 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 de bias voltage as compa red with BaTiO3-based MLCs.