Chapter 6.1 - Multi-layered Ceramic Capacitors

Abstract

Multilayered ceramic capacitors (MLCCs) are widely used in various electronic circuits. The progress of MLCC technologies has been focused on the increase of capacitance density, which is mostly realized by the reduction of dielectric layer thickness. In the section 1 , the introduction and history of MLCC will be briefly described. The reduction of dielectric layer thickness inevitably increase the electric field applied to one layer, enhancing nonlinear dielectric response caused by the ferroelectricity of dielectrics. The AC-field or DC-bias-field dependence of capacitance can be interpreted by the relaxor behavior of the shell part and depressed ferroelectricity of the core parting dielectrics as described in the section 2 . The section 3 will explain the capacitance aging, where the capacitance decreases with time under DC-bias voltages at relatively high temperature. The capacitance aging obviously decreases the performance of MLCCs in many applications. The mechanism of this phenomenon could be understood by the movement of domain walls of barium titanate at the core parts. The size effect of barium titanate will be discussed in the section 4 . The reduction of dielectric layer thickness demands the usage of the fine-grain barium titanate. The size effect of barium titanate is known as a phenomenon where the dielectric permittivity somehow decreases with decreasing grain size, and it is the biggest obstacle to develop high-capacitance MLCCs. Although the mechanism of size effect has not been completely clarified yet, recent studies using wideband dielectric spectroscopy revealed the change of polarizations with the grain size, which will give a clue to solve this problem as pointed out. Reliability measured by the lifetime in highly accelerated life test (HALT) is an important issue in MLCCs’ technology, as described. The breakdown in the HALT is caused by the accumulation of oxygen vacancies at cathodes, and grain boundaries work as the block of oxygen vacancy migrations under electric field, as shown in the section 5 . The current MLCCs’ technologies are facing on a big obstacle to further increase capacitance density because of the reliability and size effect. The limit of capacitance density obtained by the extrapolation of current technology will be predicted using computer simulation technique in the section 6 .