Papers by Keyword: Ni-MLCC

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Authors: Zhen Ji, Zhigang Xiao, Sen Wang, You Song Gu, Cheng Zhou, Yue Zhang
Abstract: In order to meet the demand on the miniaturization and manufacturing cost reduction of the multilayer ceramic capacitors we have developed a nano-BaTiO3-based non-reducible dielectric material through a soft chemical route. The particle size has been decreased down to the level of 30nm and the dielectric medium could be co-fired with Ni-electrodes under a N2+H2 reducing atmosphere. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and volume shrinkage have been employed to detect the sintering behavior and microstructure evolution including grain growth, pore formation and body densification. Dielectric measurements showed, after a sintering process at 1200°C for 2h, the dielectric constant was 8800, the dissipation factor was less than 2%, the insulation resistance was about 12~13exp Ω.cm, and the temperature coefficients of capacitance were less than 22% and -82% at -30°C and 85°C respectively. On the basis of the results it is anticipated that the material could be used for the Ni-MLCC with thin dielectric layers with a Y5V specification in the Electron Industries Association standard.
Authors: Takafumi Okamoto, Akira Ando, Hiroshi Takagi
Abstract: The electric field distributions in loaded dielectric layers of multilayer ceramic capacitors were investigated at several stages of insulation degradation for the load, using Kelvin probe force microscopy. The electric field distribution was found to be different at each stage of loaded time. Initially, the electric field was concentrated near the cathode, indicating that the insulation resistance near the anode decreased. Then, following the homogeneous distribution shown for an intermediate stage, the electric field eventually concentrated near the anode. This change indicates how insulation degradation occurs locally; this change can plausibly be explained by a hole density increase.
Authors: Makito Nakano, Akira Saito, Nobuyuki Wada
Abstract: The electrical degradation mechanisms of BaTiO3-based ceramics were investigated by measuring the dependence of leakage current on high electric fields. Before the degradation, the leakage current predominately obeyed Ohm’s law and Poole-Frenkel relation. As the degradation progressed, the Poole-Frenkel emission current increased. Moreover, the total current at the high electric fields also comprised Schottky emissions between cathodes and dielectric layers.
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.
Authors: Koichiro Morita, Youichi Mizuno, Hirokazu Chazono, Hiroshi Kishi
Authors: Makito Nakano, Akira Saito, Nobuyuki Wada
Abstract: The factors causing a decrease in the resistivity of multilayer ceramic capacitors (MLCCs) with a decrease in the thickness of dielectric layers were examined by carrying out measurements and finite element method (FEM) simulations. The obtained electric field vs. current density plots (E–J characteristics) indicated that the local concentration of electric field increased with the decrease in the thickness of the dielectric layers. The investigation of the local concentration of electric field at the grain boundaries using an FEM showed that the decrease in resistivity was caused by the roughness of the interface between dielectric layers and inner electrodes and the presence of large grains in the dielectric layers.
Authors: Kazumi Kaneda, Youichi Mizuno, Niall J. Donnelly, Soonil Lee, Wei Guo Qu, Clive A. Randall
Abstract: Re-oxidation is an important thermal process to minimize oxygen vacancies and produce high reliable Ni-MLCCs. The re-oxidation of these devices is then investigated with a series of “in-situ” impedance measurements between 400 and 500 °C in air. From the relative impedance change, chemical diffusion coefficients, associated activation energy and effective equivalent circuit model are determined. Those values were found to be reasonable compared with previous researchers’ data. Moreover, the proposed effective equivalent circuit model successfully represents the real Ni-MLCC morphology. From transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS), it is found that the electrical properties and reliabilities of the Ni-MLCCs re-oxidized under different conditions are identical.
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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