Insulation Resistance Degradation in Ni–BaTiO3 Multilayer Ceramic Capacitors

Insulation resistance (IR) degradation in Ni-BaTiO₃ multilayer ceramic capacitors has been characterized by the measurement of both time to failure (TTF) and direct current leakage as a function of stress time under highly accelerated life test conditions. The measured leakage currenttime dependence data fit well to an exponential form, and a characteristic growth time τSD can be determined. A greater value of τSD represents a slower IR degradation process. Oxygen vacancy migration and localization at the grain boundary region results in the reduction of the Schottky barrier height and has been found to be the main reason for IR degradation in Ni-BaTiO3 capacitors. The reduction of barrier height as a function of time follows an exponential relation of φ(t) = φ(0)e^-2Kt, where the degradation rate constant K = K₀e(-E_k/kT) is inversely proportional to the mean TTF (MTTF) and can be determined using an Arrhenius plot. For oxygen vacancy electromigration, a lower barrier height φ(0) will favor a slow IR degradation process, but a lower φ(0) will also promote electronic carrier conduction across the barrier and decrease the IR. As a result, a moderate barrier height φ(0) (and therefore a moderate IR value) with a longer MTTF (smaller degradation rate constant K) will result in a minimized IR degradation process and the most improved reliability in Ni-BaTiO₃ multilayer ceramic capacitors.