Papers by Keyword: Multilayer Ceramic Capacitor (MLCC)

Abstract: Multilayer ceramic capacitor (MLCC) chips have been successfully prepared through tape-casting and screen-printing. Conventional sintering method and two-step sintering method with different sintering temperature and holding time are used to obtain the MLCC chips. The scanning electron microscopes show that MLCC chips sintered by two-step sintering at T₁=1200°C and T₂=1130°C for 3h have a highly dense dielectric layer. The temperature coefficient of capacitance (TCC) of the MLCC chip is less than ±15% from-60°C to 235 °C that satisfactorily meets the requirement of X9R. The average capacitance and the dielectric loss of the MLCC chip are 88nF and 1.8% at the room temperature, respectively.

Abstract: Surface mount devices (SMDs) such as multilayer ceramic capacitors (MLCCs) have been widely used to reduce the size of electronic circuits as they are mounted directly onto the surface of printed circuit boards (PCBs) and are smaller than their through-hole counterparts because SMDs have shorter internal leads or no leads at all. Another advantage of these components is the lower parasitic inductance, which results in a higher resonant frequency. This work reports on the dielectric characterization of four commercial multilayer ceramic capacitors in a broad frequency range from 0.01 GHz to 2 GHz. The dielectric characterization consists of measuring the reflection coefficient S₁₁ (real and imaginary parts) as function of frequency to calculate the permittivity, impedance and loss tangent of the capacitors tested. In addition, dielectric chemical composition is determined using surface X-ray spectroscopy (EDS). The results show that MLCCs have a resonance frequency higher than 0.3 GHz depending on the value of their capacitance, making them suitable for use in RF equipment, mobile phones, radars, and microwave electronic circuits.

Abstract: Uniform BaTiO₃ polycrystalline coating layer on Ni nanoparticles is achieved by a novel sol-precipitation method. The Fourier transform infrared spectra (FT-IR) of the coated samples inhibit that there is typical Ba-O and Ti-O bond for crystalline BaTiO₃.The influence of reaction time on the properties of the coated samples is investigated. It is found that the coating layer contains less BaCO₃ impurity and crystallizes more completely along with the increase of the reaction time. Moreover, the anti-oxidation properties of these samples are significantly improved.

Abstract: With the advance of microelectronics technologies and integrated circuits (ICs) processes, the electrostatic discharge (ESD) has become one of the most important reliability issues in IC products. But treating the ESD-related problems is a real challenge. The paper focuses on the influence of the using of Universal Serial Bus (USB) in plugging and/or unplugging impact arisen from ESD and also proposes an ESD protection design to improve the ESD robustness. This work utilizes off-chip protection along with the commercial ceramic products to achieve effective ESD protection. The impact of the ESD stress applied at the connector pins of USB is evaluated. The protection design for the high-speed signal lines is easily to implement and achieves the following attractive features: (1) Power trace protection, (2) Signals traces protection, (3) GND protection, and (4) Shield protection. Numerous tests have been made to demonstrate the effectiveness of the work.

Abstract: We present the technology of obtaining and the main properties of multilayered ceramic capacitors (MLCC) based on the PMN-PT-PFN solid solution. PMN-PT-PFN is the abbreviation of the material with general formula (1-y)[(1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3]-yPb(Fe1/2Nb1/2)O3. In our work the investigated material was PMN-PT-PFN with x=0.25, y=0.1 i.e. 0.9(0.75PMN-0.25PT)-0.1PFN. The powder of 0.9(0.75PMN-0.25PT)-0.1PFN has been obtained in three steps. In first step we obtained MgNb2O6. In second step FeNbO4 was obtained. In final third step the 0.9(0.75PMN-0.25PT)-0.1PFN was obtained from mixed powders MgNb2O6, FeNbO4, PbO and TiO2. Thick film pastes for obtaining MLCC were prepared by mixing of PMN-PT-PFN powder with organic vehicle and firing in furnace in the temperature range up to 1050°C. Platinum paste has been used as electrodes. The thickness of single layer was about 45 µm (including electrodes). For obtained MLCC XRD investigations were performed as well as investigations of microstructure, EDS and main dielectric properties.

Abstract: The conventional finite element method (FEM) cannot investigate the size effect on thermal residual stresses induced by the sintering process in micro multilayer ceramic capacitors (MLCCs). In this paper, a FE two-dimensional single layer model is developed for investigation of the effect of the micro scale on prediction of the residual thermal stresses in MLCCs. In this FE single layer model, the strain gradient effect is considered. It is found that with decreasing single layer thickness, the shear stress increases significantly in the ceramic layer near the electrode tip, which might cause cracking of the ceramic layer near the electrode tip. The numerical results also show that the predictions of the thermal residual stresses in MLCCs are strongly dependent on the micro scale. The residual thermal stresses induced by the sintering process exhibit strong size effects and, therefore, the strain gradient effect should be taken into account in the design and evaluation of MLCC devices.

Abstract: In this paper, the effect of Nb₂O₅ on the microstructure and dielectric properties of BaTiO₃-based ceramics has been investigated. In the study，Nb₂O₅ is added to the BaTiO₃-based ferroelectric material by conventional solid state synthesis. The structure is identified by X-ray diffraction method and SEM is also employed to observe the surface morphologies of the sample. The specimens of the ferroelectric doped with 2wt% Nb₂O₅ sintered at 1260°C for 1h exhibit attractive properties, its dielectric temperature coefficient is lower than 15% over a wide temperature range from －55 to +180°C.

Abstract: The role of grain boundaries (GBs) in the diffusion of oxygen vacancies (VO••s) in barium titanate (BaTiO3) and its mechanism were investigated using atomistic simulation techniques. It was found that GBs trapped VO••s at specific sites in the course of the diffusion, and the excess energy reflecting structural distortion of the GB was closely related to the availability of the trapping. GBs therefore act as a resistance of the diffusion of VO••s, suggesting that electrical degradation of multilayer ceramic capacitors (MLCCs), which is derived from vacancy diffusion, enables to be additionally improved by controlling GB structures in BaTiO3-based dielectrics.

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.

Abstract: BaTiO3 powders with particle size 0.1μm were made by solid state synthesis. To make high tetragonality BaTiO3 powder, mixture of TiO2 and BaCO3 was calcined in vacuum condition. And to make low tetragonality BaTiO3 powder, the mixture was calcined in air condition. With each powder, MLCCs with Ni-internal electrode were fabricated. Relationships between temperature and relative dielectric constant of MLCCs’ dielectric layers were analyzed and their dielectric grains were observed by TEM-EDS. As the result, MLCC made from high tetragonality BaTiO3 powder had good temperature characteristics and core-shell dielectric grains.