Construction of lead-free dielectrics for high temperature multilayer ceramic capacitors and its inner electrode matching characteristics

Abstract

High-temperature multilayer ceramic capacitors (HT-MLCCs) are indispensable key basic components in high-temperature electronic equipment. Obtaining practical HT-MLCCs requires not only a high-temperature dielectric with excellent temperature stability, but also a good match between the inner electrode and the dielectric. In this work, a quaternary lead-free system (1-x) (0.64Na0.5Bi0.5TiO3-0.16 K0.5Bi0.5TiO3-0.20Bi(Mg2/3Nb1/3)O3)-xCaZrO3 (NBT-KBT-BMN-xCZ) was investigated as candidates for high-temperature dielectric. The introduction of CZ can adjust the composition of different types of polar nanoregions (PNRs) and weaken the ferroelectric coupling behavior, thereby achieving the flattening of the dielectric temperature curve. Among all the components, NBT-KBT-BMN-0.06CZ (0.06CZ) has the most excellent high-temperature dielectric properties, and is further used to match the two inner electrodes of Pt and Ag/Pd to make HT-MLCCs. The results show that for Pt-MLCC, co-firing causes a second phase MgTi2O5 to appear at the heterogeneous interface, resulting in incomplete inner electrodes, lower dielectric permittivity and increased loss in the high-temperature region. In contrast, for Ag/Pd-MLCC, the heterogeneous interface is well bonded, the inner electrode is continuous and complete and there is no second phase, which makes the capacitor show excellent dielectric performance (εr=1393±15%, tanδ≤0.025) over a wide range of 129–404 °C. This work provides an important solution for the development of a new generation of HT-MLCCs.