Kiyoji Handa

High Volume Efficiency Multilayer Ceramic Capacitor

Multilayer ceramic (MLC) capacitor with small size, large capacitance and low cost are increasingly demanded as components for miniaturized electronic equipment. The conventional dielectric materials for MLC capacitors are mainly based on BaTiO3 . They are co-fired in air with internal electrodes at around 1,300 oC.) Therefore, the internal electrodes must be a precious metal, such as platinum or palladium, in order to prevent oxidation or reaction with dielectrics. In the case of large capacitance MLC capacitors, the precious metal cost constitutes large proportion of the selling price of the capacitor. So, large capacitance MLC capacitor is too expensive for consumer electronics applications.

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 x 1.6 x 1.5 mm) were fabricated. The MLCs were fired at 1000°C for 2h and the grain size was 1.3 μm. The capacitance per unit volume of these MLCs is approximately 900 μF/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 dc bias voltage as compared with BaTiO 3 -based MLCs.

Relaxor Dielectric Materials for Multilayer Ceramic Capacitor in High-Temperature Applications

A relaxor ceramic dielectric based on the (Pb, Ba)[(Zn 1/3 Nb 2/3 )(Mg 1/3 Nb 2/3 )Ti]O 3 system has been developed for multilayer ceramic capacitors (MLC) in high-temperature applications. This dielectric material is designed to exhibit a capacitance peak value at around 60°C, which is a typical temperature inside a switching mode power supply (SMPS). An MLC fabricated using this new dielectric and fired at 1050°C has a relative dielectric constant of 9000 and a CR product (capacitance x resistance) of 8000 ΩF at room temperature. However, at 60°C the relative dielectric constant is 14000 and the CR product is 4000 ΩF. The change in capacitance with temperature is less than -30% from 0 to 125°C. This makes the new MLC a promising candidate for use as a filter capacitor in highfrequency SMPS.

Medium Voltage Large Capacitance Multilayer Ceramic Capacitors Employing Lead Perovskite Ferroelectric Material

Multilayer ceramic capacitors (MLCs), having 1 µF actual capacitance value at 200 V, have been fabricated using modified lead zinc niobate-lead magnesium niobate-lead titanate relaxor dielectric material. The MLCs can meet each of Y5U and Y5S specifications in Electronic Industries Association (EIA) standard. These MLCs are promising candidates replacing conventional film capacitor or aluminum electrolytic capacitor,especially for the medium voltage application such as a input filter of switching power supply in a high frequency region.