Microstructural Analysis of X7R-Type BaTiO3 Multilayer Ceramic Capacitors (MLCCs)

Abstract

The microstructures of typical commercial X7R MLCCs were characterized by transmission electron microscopy (TEM), using tripod polished specimens and ion milled samples. Core-shell structures were clearly observed in the TEM specimens, and glass phases located at the grain boundaries and triple points were frequently observed. Their chemical composition was analyzed using energy dispersive X-ray spectrometry (EDS), which showed bismuth ions diffused into the shell regions, while the cores were pure BaTiO 3 . X-ray diffraction (XRD) suggested that the predominant phase in the microstructure had pseudocubic global symmetry, while ferroelectric domains were observed in TEM bright field (BF) images. The internal electrodes in the devices were an alloy of Ag/Pd, and these regions were found to have twinned crystal structures. The stress states in the interfaces between the electrodes and the dielectric layers were revealed, and no silver migration in the flux at the electrode-dielectric interfaces was observed.

Evaluation of Residual Stress in a Multilayer Ceramic Capacitor and its Effect on Dielectric Behaviors Under Applied dc Bias Field

“…M ultilayer ceramic capacitor (MLCC), an essential electronic device consisting of alternate layers of metal electrodes and dielectric ceramics sandwiched between two ceramic cover layers, is widely used in surface‐mounted circuits because of its high capacitance density and small size. In recent years, in order to meet the requirements for further miniaturization and higher capacitance of digital electronic equipments, the thickness of dielectric layer in the MLCC greatly reduces; meanwhile, the number of the dielectric layers is progressively increasing 1–4 . However, because of introduction of two dissimilar materials with different coefficients of thermal expansion (CTE) in manufacturing process, the MLCC is generally subjected to residual stress, which is responsible not only for structural failures such as cracks, delamination, and deformation but also for modification of the dielectric behavior of dielectric layers 5–10 .…”

“…In recent years, in order to meet the requirements for further miniaturization and higher capacitance of digital electronic equipments, the thickness of dielectric layer in the MLCC greatly reduces; meanwhile, the number of the dielectric layers is progressively increasing. [1][2][3][4] However, because of introduction of two dissimilar materials with different coefficients of thermal expansion (CTE) in manufacturing process, the MLCC is generally subjected to residual stress, which is responsible not only for structural failures such as cracks, delamination, and deformation but also for modification of the dielectric behavior of dielectric layers. [5][6][7][8][9][10] Investigation of stress evolution in the MLCC is very essential for improvement in reliability and lifetime of the MLCC; thus there has been much interest in characterization of the residual stress in the MLCC so far.…”

Effect of Oxygen Partial Pressure on the Dielectric Properties and Microstructures of Cofired Base‐Metal‐Electrode Multilayer Ceramic Capacitors

“…The dielectric constant–temperature curve can be optimized by doping chemical shifters, pinchers, and depressors to meet the Electronic Industries Alliance (EIA) standards such as X7R and Y5V 9–11 . X7R MLCCs usually have core–shell microstructures, 9–14 where the shell region is a solid solution of BaTiO 3 containing many dopants, while the core is nearly pure BaTiO 3 . As a result of its characteristic diffuse phase transitions, the shell material has been shown to have a broad dielectric maximum peak in many such systems 15–19 .…”

Role of Liquid Phase in Achieving a Fine Microstructure and Diffusive Phase Transition of MgO‐Doped BaTiO3

“…Importantly, elements Ba and Ti are detected apparently in the glass phase due to the formation of barium‐rich titania‐based liquid 22,23 . It clearly indicates that BaTiO 3 is partially dissolved into the liquid phase, …”

“…Reaction () means that in order for dopants such as Mg to be doped to BaTiO 3 , actually BaTiO 3 has to be partially decomposed to BaO and TiO 2 first. From the evidence of the partial dissolution of BaTiO 3 to yield the barium‐rich titania‐based liquid, 22,23 the partial dissolution into the liquid by reaction () can be the necessary decomposition reaction. Then, MgO and TiO 2 react to be doped onto a BaTiO 3 lattice by reaction ().…”