Papers by Author: Hirokazu Chazono

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Authors: Koichiro Morita, Youichi Mizuno, Hirokazu Chazono
Abstract: The lifetime determination model for multilayer ceramic capacitors (MLCCs) is discussed. The accumulation of oxygen vacancies on the cathode/ceramics interface by an electro-migration process is a concept accepted by many researchers. However, the lifetimes and leakage currents measured during a highly accelerated lifetime test (HALT) could not be explained by this concept. To investigate the mechanism, we used a polarity reversal method during the HALT, which provided information on the dominant process for the leakage current. Thermally stimulated current (TSC) measurement provided the relative number of oxygen vacancies both on the cathode/ceramics interfaces and the grain boundaries. Moreover, the microstructure of the MLCC samples was evaluated by both electric property measurements and direct observation. From these results, we concluded that the grain boundaries controlled the leakage current as well as the lifetime.
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Authors: Koichiro Morita, Youichi Mizuno, Hirokazu Chazono, Hiroshi Kishi
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Authors: Satoshi Yokomizo, Takuya Hoshina, Hiroaki Takeda, Katsuya Taniguchi, Youichi Mizuno, Hirokazu Chazono, Osamu Sakurai, Takaaki Tsurumi
Abstract: We researched the phenomenon that the permittivity of dielectric layers in multilayer ceramic capacitor (MLCC) increases with the number of dielectric layers. Finite element method (FEM) shows that the internal residual stress in MLCC was generated by the difference of thermal expansion coefficient between internal electrodes and dielectric layers. We developed a electric measurement system with applying external stress for understanding the stress influence on dielectric properties. The compressive stress along electric field increased the polarization. The polar nano regions (PNRs) in shell composition dielectrics were easily influenced by stress. Based on these results, the relationship between the number of dielectric layers and their permittivity in MLCCs was explained.
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Authors: Tatsuo Sakashita, Kentaro Nakamura, Giuseppe Pezzotti, Hirokazu Chazono
Abstract: Residual stresses in Ni-MLCC were investigated by Raman microprobe piezo-spectroscopic (PS) methods. The shape of the Raman spectrum of BaTiO3 in Ni-MLCC depended on the angle between the polarizing direction of the incident laser beam and the direction of the internal electrode. From a set of precise calibrations, we show that the orientation dependence arises from the interaction between internal stresses and the polycrystalline microstructure; by taking into account such an orientation dependence, we were able to establish a technique for the measurement of the distribution of residual stresses in Ni-MLCC.
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