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

Abstract

Raman spectroscopy is used to evaluate migration behavior of oxygen vacancies in BaTiO 3 -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 BaTiO 3 that is associated with oxygen vibration was hardened and broadened near the Ni electrodes before HALT. However, the hardening and broadening of the B 1 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.

Formation of structural defects and strain in electrodegraded Fe‐doped SrTiO3 crystals due to oxygen vacancy migration

“…The result is interpreted as the presence of Jahn‐Teller distorted Fe 4+ centers (see Figure C) at the oxidized planar (B045) crystal's anode. In addition, the Raman peak at 300 cm −1 (B1‐mode) was also used to assess in‐plane stretching/compressing of the oxygen sublattice (along the crystallographic ab‐ plane). B1‐modes appear at both anode and cathode interfaces, and we show that the B1 Raman shift at the reduced crystal's anode is much lower than that of the oxidized crystal's anode, marking longer in‐plane oxygen bonds at reduced planar (B042)'s cathode.…”

Effect of rare-earth (RE) ionic radius on the dielectric properties of Sr99%RE1%TiO3 (RE = La, Nd, Yb) single crystals

“…In our case, all samples have two strong scattering bands in the range of 220–400 cm −1 and 600–750 cm −1 , which is a classical cubic second-order Raman mode, 52 and the Raman peak at about 300 cm −1 is an in-plane vibrational mode of the oxygen sublattice (B 1 mode). 53 Compared with the Raman peak of the SrTiO 3 crystal (303.2 cm −1 ), the Raman peaks of the La, Nd, and Yb doped crystals are shifted to 309.5 cm −1 , 308.4 cm −1 and 306.3 cm −1 , respectively. The change in Raman peak position is related to the non-centrosymmetric Jahn–Teller distortion due to the accumulation of oxygen ions.…”

Analyses of microstructure at degraded local area in Ni-multilayer ceramic capacitors under highly accelerated life test

“…The degradation of MLCCs is considered to be caused by the electromigration of oxygen vacancies from anode to cathode under high temperature and high voltage. 2,3) There have been a lot of studies on microstructures of MLCC, in terms of dielectric thickness, 4) grain size, [5][6][7] shell formation in BaTiO 3 grain, [8][9][10] occupation site of additive ions, 1,[11][12][13] crystal orientation, 14) and segregated phase. 15) With regard to the works of grain size, studies were on the dependence of lifetime on average number of grains, [5][6][7] distribution analyses of oxygen vacancies in degraded BaTiO 3 , 2,3) and discontinuous steps at grain boundary related to oxygen vacancy.…”