Raman Spectroscopy Evaluation of Oxygen Vacancy Migration by Electrical Field in Multilayer Ceramic Capacitors

Raman spectroscopy is used to evaluate migration behavior of oxygen vacancies in BaTiO3-based multilayer ceramic capacitors with Ni internal electrodes (Ni-MLCCs) before and after a highly accelerated life test (HALT). The B-1 phonon mode of BaTiO3 that is associated with oxygen vibration was hardened and broadened near the Ni electrodes before HALT. However, the hardening and broadening of the B, mode were observed near the cathodes after HALT. It is considered that the oxygen vacancies were localized near the Ni electrodes before HALT and they electromigrated toward the cathode because they have the positive charges. These results show that oxygen vacancies migrated and accumulated near the cathode under a dc bias and caused insulation resistance degradation in MLCCs. In addition, Raman spectroscopy is a powerful tool for investigation of structural defect distribution including oxygen vacancies with a relatively high spatial resolution. (C) 2009 The Japan Society of Applied Physics