An investigation on the on dielectric, ferroelectric properties and failure mechanism for the 0805X7R multi-layer ceramic capacitor

The BaTiO3-based multi-layer ceramic capacitors (MLCCs) has been widely used with the development of the automobile, personal computers and other electronic equipment. As the most important performance parameter of MLCCs, the reliability is mainly affected by grain size, oxygen vacancy concentration and migration energy, which has been generally accepted. However, there is not a comprehensive and profound understanding for the failure mechanism of MLCCs. Generally, the failure sample mainly shows aggregation of oxygen vacancies, resulting in a large drop in resistance. Actually, the change in the micro-structure of the failure sample can also be reflected by the dielectric and ferroelectric properties. In this work, two 0805 MLCCs devices with a BaTiO3dielectric layer of ~4μm, including a normal sample without aging and a failed sample manifested as a resistance drop of one order after aging at 125 ℃, 37.5 V for 168 h, were investigated. We demonstrated the capacity of failure sample decreased and the dielectric loss increased comparing the normal sample. For the ferroelectric properties, all the samples show that the coercive electric field and residual polarization increase with the temperature increasing, while the symmetry of the hysteresis loop and the Pmax(Maximum polarization) decreased for the failure sample. Furthermore, we also proved that the Schottky barrier of the Ni-BaTiO3interface layer decreased from 0.6eV to 0.4eV after aging, which was mainly caused by oxygen vacancy migration interpreted by the measurement and analysis of XPS (X-ray photoelectron spectroscopy), IV in different temperature, SKPM (Scanning Kelvin probe microcope). At last, the migration mechanism model of oxygen vacancy is established for further exploration of the failure mechanism.