Kinetics of oxygen diffusion into multilayer ceramic capacitors during the re-oxidation process and its implications on dielectric properties

The re-oxidation process is an important thermal processing step to minimize oxygen vacancies and to produce a high resistivity and more reliable multilayer ceramic capacitors (MLCC) upon co-firing with Ni internal electrodes. A model X7R capacitor based on Ho₂O₃ amphoteric doping is investigated in prototyped multilayer devices. The dielectrics are co-fired in a standard low pO₂ sintering process. The re-oxidation thermal process of these multilayer devices is then investigated with a series of "in-situ" impedance measurements. These measurements are performed in a temperature range from 400° to 500°C in air. The relative impedance change is used to determine effective chemical diffusion coefficients and associated activation energy. The electrical conductivity is analyzed to determine properties, such as Schottky barrier height and degradation lifetime, under different re-oxidation conditions. Furthermore, transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) are applied to consider the microstructure, microchemistry, and oxygen stoichiometry changes.