BST Ceramics For Middle-high Voltage Capacitors

The rapid development of mobile communication, digital appliances and radar devices required middle-high voltage multilayer ceramics capacitor (for short, MLCC) with excellent breakdown performance and lower cost of manufacturing. Therefore, the development of ceramics for middle-high voltage MLCC was mainly focused on high voltage, anti-reduction and low temperature sintering.(Ba,Sr)TiO₃ (for short, BST) ceramics is of adjustable dielectric performance and one of the highlight of dielectric materials research. Presently, the investigation on breakdown performance of BST ceramics was mostly focused on preparation technique and addition of lead. Based on the requirement of middle-high voltage MLCC for lower cost and lead-free, and on the current development and existing problems of materials for middle-high voltage MLCC, niobium and magnesium were co-doped into BST ceramics by solid reaction to enhance the breakdown electric field. The resistance of BST ceramics with niobium and magnesium co-doped was improved by reducing titanium content. With the co-addition of lithium fluoride and alumina, the sintering temperature of the ceramics was lowered, which fill the requirement of middle-high voltage MLCC for cofiring with lower Pd content electrode.The effect of niobium and magnesium co-doping on the dielectric performance of BST ceramics was investigated. Niobium and magnesium co-doping into BST ceramics could flatten the dielectric constant peak and enhance the breakdown electric field.Sintered at 1320℃ ,Ba_0.9Sr_0.1(Nb₍2/3Mg_1/30.04Ti_0.96O₃ ceramics had excellent dielectric performance with ε_r=1053, E_b=13kv/mm, tgσ =0.01, ρ>10¹⁰Ω·cm.The effect of titanium content on the dielectric performance of BST ceramics was investigated. The effect of titanium content on the dielectric performance of BST ceramics was investigated for improving the ceramics' resistance. It was found reducing titanium content improved the ceramics' resistance, but decreased the breakdown electric field for the second phase Ba_1.91Sr_0.09TiO₄ appearance.Low-temperature sintering of BST ceramics for middle-high voltage MLCC was investigated. The sintering temperature of BST ceramics was decreased from 1370*0 to1150*C when lithium fluoride and alumina were co-added into BST matrix and lowmelting point compounds appeared. BaAkC^ was formed by the reaction between AI2O3 and (Ba,Sr)O which restrained the appearance of Bai.9iSro.o9Ti04.Therefore,the breakdownelectric field of BST matrix was enhanced, sintered at 1150 °C, Bao.9Sro.i(Nb2/3Mgi/3)o.o4Tio.96(i -o.25)03 ceramics with the co-addition of 1.5wt%LiF+5wt%Al2O3 gave excellent dielectric properties: er=l055> Eb=15.6kv/mm> tgo =0.0025-. P =2.8><1011Q?cm .