Dielectric Degradation and Microstructures of Heterogeneous Interfaces in Cofired Multilayer Ceramic Capacitors

The compatibility of electrodes and dielectrics in cofired MLCCs with both Ni and Ag/Pd electrodes was characterized by transmission electron microscopy (TEM) using tripod polished samples. Tripod polishing procedures can reduce entire devices to a thickness of less than 1 m. After low angle ion milling for a short time, many regions across several dielectric and electrode layers are electron transparent, which makes it possible to characterize the cofired interfacial microstructures. When analyzed by convergent beam electron diffraction (CBED) and energy dispersive X-ray spectrometry (EDS), NiO lamellae and P-rich intermediate layers were found in highly accelerated life tested (HALT) MLCCs with Ni electrodes. CBED confirmed that the P-rich layers had a Ba₄Ti₁₃O₃₀ (B₄T₁₃) structures. Oxidized Ni layers containing Mn were also found in the HALT samples. It is believed that Mn ions were reduced by the Ni electrodes, as P-rich and Mn-rich segregated layers were observed in the virginal non-life tested MLCCs. Grains with stacking faults, containing dopants such as Mn, Si, and Mg, had the BaTi₄O₉ (BT₄) structure. No silver diffusion was found in either the BaTiO₃ based perovskite lattices or the flux phases in air-fired X7R type MLCCs.     

Microstructural Analysis of X7R-Type BaTiO<Subscript>3</Subscript> Multilayer Ceramic Capacitors (MLCCs)

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 BaTiO₃. 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.     

Copper Cofire X7R Dielectrics and Multilayer Capacitors Based on Zinc Borate Fluxed Barium Titanate Ceramic

Copper cofired dielectrics may give new opportunities for high temperature capacitors. To demonstrate feasibility, BaTiO₃ has been formulated into X7R dielectrics with copper inner electrodes. This requires the development of a formulation that permits sintering at temperatures below 1000°C, and then firing in a reducing environment in atmospheres pO₂ 10^–8 atms. ZnO—B₂O₃ chemistries were explored with additional dopants to modify densification and the temperature coefficient of capacitance of the BaTiO₃ dielectric anomaly. X7R characteristics with relative dielectric permittivities 2750 and tan 0.01 at 1 kHz were obtained at room temperature. Multilayer capacitors were fabricated in 3.2 mm × 1.6 mm size multilayers with an acrylic binder system and oxidation resistive copper inner electrodes.     

Effect of Interactions at the Cofired Interface of Electrode/Ceramics on the Reliability of Lead-Based Multilayer Ceramic Capacitors

The increase of silver content in the internal electrodes was found to have a negative influence on accelerated-test life of lead magnesium niobate-based multilayer ceramic capacitors under direct current-voltage. Transmission electron microscopy (TEM) and auger electron spectroscopy (AES) analyses were carried out on the cofired electrode/ceramics interfaces to demonstrate the effect of Ag content in the electrode on the reliability of capacitors. The result showed that Ag could diffuse into the ceramic layers for more than one micrometer. We designed Ag-doping experiments to study the interactions between the ceramics and Ag. Temperature-humidity-bias (THB) tests on Ag-doped disc specimens revealed that the failure rate of the specimens increased with the Ag content in the ceramics. Based on these results, it was inferred that the deterioration of the multilayer ceramic capacitors with the increase of Ag content in the electrodes should be attributed to the Ag diffusion from the electrodes into the oxide ceramics.     

特高压串补线路沿线电压分布及串补布置方案研究

提出一种基于传输线理论的特高压串补输电线路电压分布的快速算法。首先,将线路的传输参数矩阵转化为两端口节点导纳矩阵,得到∏型等值模型集总参数。然后将其填入潮流计算软件,对目标电网进行潮流计算。再将计算的结果作为末端边界条件,用传输参数矩阵就可快速得出线路上的电压分布。该算法可精确计算特高压串补线路的沿线电压分布情况,而且还可以计及线路两侧的无功补偿能力,工程适用性很强。最后,还从理论上研究特高压串补的集中／分散布置方案以及串补和高压电抗的相对布置位置,指出高压电抗位于母线侧且串补分散布置的方案比高压电抗位于线路侧且串补集中布置的方案更有利于抑制工频稳态过电压,为特高压输电工程规划给出了指导性建议。     

Luminescence Characteristics of YAG Glass–Ceramic Phosphor for White LED

Luminescence characteristics of Ce:Y₃Al₅O₁₂ (YAG) glass-ceramic (GC) phosphor for a white LED were investigated. The GC phosphor was obtained by a heat treatment of a Ce-doped SiO₂-Al₂ O₃-Y₂O₃ mother glass between 1300degC and 1500degC for the prescribed time period. The quantum efficiency (QE) of Ce³⁺ fluorescence in the GC materials, the color coordinate, and the luminous flux of electroluminescence of LED composite were evaluated with a blue LED (465 nm) set in an integrating sphere. The QE increased with increasing ceramming temperature of the as-made glass. The color coordinates (x, y) of the composite were increased with increasing thickness of the GC mounted on a blue LED chip. The effect of Gd₂O₃ substitution on the optical properties of the GC materials was also investigated. The excitation and emission wavelengths shifted to longer side up to Gd/(Y + Gd) = 0.40 in molar composition. As a result, the color coordinate of the LED with GdYAG-GC of various thickness shifted to closer to the Planckian locus for the blackbody radiation. These results were explained by partial substitution of Gd³⁺ ions in the precipitated YAG microcrystals, leading to the increase of lattice constant of unit cell, which was confirmed by XRD.     

Thermal and Mechanical Analysis of High-Power LEDs With Ceramic Packages

In this paper, we present the thermal and mechanical analysis of high-power light-emitting diodes (LEDs) with ceramic packages. Transient thermal measurements and thermomechanical simulations were performed to study the thermal and mechanical characteristics of ceramic packages. Thermal resistances from the junction to the ambient were decreased from 79.6 to 46.7degC/W by replacing the plastic mold with a ceramic mold for LED packages. Thermomechanical stress induced in the heat-block test was simulated using a finite-element method. Higher level of thermomechanical stress in the chip was found for LEDs with ceramic packages, despite less mismatching coefficients of thermal expansion, compared with that with plastic packages. The thermomechanical-stress components in the direction of the thickness were found to be larger than that in other two directions. The results suggest that the thermal performance of LEDs can be improved by using ceramic packages, but the mounting process of the high-power LEDs with ceramic packages is critically important and should be the reason for causing delaminating interface layers in the packages.     

XPS Studies of PZT Films Deposited by Metallic Lead and Ceramic PZT Dual Target Co-Sputtering

The dependence of the chemical states of the constituent elements of a PZT thin film prepared by RF magnetron co-sputtering using ceramic PZT and metallic Pb dual target materials on the Ar⁺ etching time was studied using XPS. The metallic Pb, lead oxide and Pb in PZT led to the different binding energies of the Pb lines. The intensity of binding energy of metallic Pb relative to that of bulk Pb increased with the depth of the film. The peak position and the line shape of the O_1s electron was associated with the different binding energies of oxygen, which interacts with Pb and Ti and Zr atoms to form the metal oxides, and the softening of the O_1s bonds by the bonding interaction in Ti–O, Zr–O and Pb–O. The broad Ti_2p3/2 line in the PZT film could has been associated with the various charge state of Ti and no spectral changes of Ti_2p and Zr_3d were observed as the Ar⁺ ion sputtering time was increased.     

Design Optimization of Wind Power Planning for a Country With Low–Medium-Wind-Speed Profile

The emerging energy crisis resulting from a high price of crude oil has drawn attention about renewable energy all over the world. Thailand is a developing country located at the heart of Southeast Asia, with about 66 million of population as of 2006. The electricity supply industry structure under the government of Thailand has been managed by the Electricity Generating Authority of Thailand, the Metropolitan Electricity Authority, and the Provincial Electricity Authority for almost 50 years. According to the 2004 Power Development Plan, the country would have generation reserve at a marginal of 15%. Due to the rapid economic growth and difficulty in building new centralized generating facilities, this has the potential to create a security issue of electricity energy shortage and may develop a severe system blackout. Renewable energy issues have been widely discussed and debated over the country. Although solar energy is the most prominent renewable energy source due to the appropriate geographic of Thailand, it is still considered as a low-density energy source which requires a large area of installation. Therefore, for the long-term investment, wind power seems to be a good candidate because it is quick to install, needs no fuel cost, and is environment friendly. Therefore, this paper investigates the impact of the penetration level of wind power generation to be integrated into the Thailand system. System stability has been observed in various system configuration changes due to different control strategies of wind farms. The economic analysis of wind-farm investment has been also considered.      

电感耦合等离子体发射光谱法测定陶瓷制品中铅、镉迁移量的不确定度评定

对电感耦合等离子体发射光谱法测定陶瓷制品中铅,镉迁移量的不确定度进行评定,分析不确定度的主要来源,评估检测过程中不确定度分量。检测结果的不确定度主要来源于测量重复性和标准曲线的非线性。     

Interfacial electrostatic phenomena and capacitance–voltage characteristics of ultrathin polyimide Langmuir–Blodgett films

Capacitance–voltage (C–V) characteristic of ultrathin polyimide (PI) Langmuir–Blodgett (LB) films is discussed theoretically and experimentally taking into account the interfacial electrostatic phenomena and interfacial electronic states at the metal/PI LB film interface. It was found that the apparent film thickness decreases due to the charge exchange phenomena at the metal/film interface. It was also found that electrical insulating properties of the Au/PI LB film/Al device depended on the polarity of external voltage, probably due to the formation of the electrostatic interfacial electric field of 10⁸ to 10⁹ V/m. © 2000 Scripta Technica, Electr Eng Jpn 134(3): 9–15, 2001     

Evaluation of Head Orientation and Neck Muscle EMG Signals as Command Inputs to a Human–Computer Interface for Individuals With High Tetraplegia

We investigated the performance of three user interfaces for restoration of cursor control in individuals with tetraplegia: head orientation, electromyography (EMG) from face and neck muscles, and a standard computer mouse (for comparison). Subjects engaged in a 2-D, center-out, Fitts' Law style task and performance was evaluated using several measures. Overall, head orientation commanded motion resembled mouse commanded cursor motion (smooth, accurate movements to all targets), although with somewhat lower performance. EMG commanded movements exhibited a higher average speed, but other performance measures were lower, particularly for diagonal targets. Compared to head orientation, EMG as a cursor command source was less accurate, was more affected by target direction and was more prone to overshoot the target. In particular, EMG commands for diagonal targets were more sequential, moving first in one direction and then the other rather than moving simultaneous in the two directions. While the relative performance of each user interface differs, each has specific advantages depending on the application.      

Systematic Study of the Dopant-Dependent Properties of Electrically Programmable Fuses With Silicided Poly-Si Links Through a Series of I– V Measurements

Electrically programmable/writable fuses (e-fuses) with a Ni-silicided polycrystalline silicon narrow link and fabricated with four doping conditions were studied using two successive I-V measurements. The initial I-V sweeps can change e-fuses into targeted programmed states and display all of the programming processes where the currents change by many orders of magnitude. The second set of I-V curves can show stability and conduction in the programmed states for both bias polarities. Through the series of I-V measurements, the two-step programming with moderate blowing conditions could be reproduced and studied systematically. The programming processes of incompletely programmed states, before complete programming (CP), were found to be strongly dependent on the dopant conditions. The origin of the dopant dependency was considered within a simple electrical equivalent circuit model. At least two or three programmed states were identified among the completely programmed states in terms of the characteristic spreads of the final resistance and conduction behavior. The most distinctive currents after CP are similar to those in varistors. The stability of every programmed state is strongly dependent on the dopant conditions.     

Strain–magnetization properties and domain structures of silicon steel sheets

The effects of tensile stress and strain on magnetization and magnetic domains in silicon steel sheets were investigated. In the elastic deformation region, magnetization decreased with an increase in strain, while in the plastic deformation region, strain–magnetization properties under stress showed a peculiar characteristic, namely, an increase of magnetization when strain was decreased. We observed lancet and other domains in the specimens after removing the stress applied in the plastic deformation region, especially near grain boundaries. This phenomenon can be explained by changes in the domain structures, which were observed in this study. The features observed in this investigation can be applied to the nondestructive detection of fatigue in metal magnetic materials. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(2): 10–17, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20002     

Separation conditions and criteria for uniform approximation of input–output maps

We consider multidimensional shift-invariant input–output maps G from a relatively compact set of functions S to a set of real-valued functions, and we give criteria under which these maps can be uniformly approximated arbitrarily well using a certain structure consisting of a not-necessarily linear dynamic part followed by a non-linear memoryless section that may contain sigmoids or radial basis functions, etc. The dynamic part is comprised of a finite number of dynamic maps h₁,…,h_j drawn from a set H of maps that satisfy a certain continuity condition. In our results certain separation conditions, of the kind associated with the Stone–Weierstrass theorem, play a prominent role. Here they emerge as criteria for approximation, and not just sufficient conditions under which an approximation exists. In particular, one of the theorems given is a result to the effect that universal approximation can be achieved using the structure we consider if and only if the set H satisfies the separation condition that (hu₁)(0)≠(hu₂)(0) for some h∈H whenever u₁,u₂∈cl(S) and u₁≠u₂ (where cl(S) denotes the closure of S). This holds even if the elements of H are not linear. © 1998 John Wiley & Sons, Ltd.     

Analysis and implementation of a high‐efficiency zero‐voltage‐zero‐current‐switching DC–DC converter

A high‐efficiency zero‐voltage‐zero‐current‐switching DC–DC converter with ripple‐free input current is presented. In the presented converter, the ripple‐free boost cell provides ripple‐free input current and zero‐voltage switching of power switches. The resonant flyback cell provides zero‐voltage switching of power switches and zero‐current switching of the output diode. Also, it has a simple output stage. The proposed converter achieves high efficiency because of the reduction of the switching losses of the power switches and the output diode. Detailed analysis and design of the proposed converter are carried out. A prototype of the proposed converter is developed and its experimental results are presented for validation. Copyright © 2011 John Wiley & Sons, Ltd.     

Evaluation of load division among transformers of different capacities in the grounded wye–delta and open wye–open delta banks under balanced loading and various power factor conditions

This paper evaluates the load division among transformers of different capacities in the grounded wye–delta and open wye–open delta banks under balanced loading and various power factor conditions. In some contingency cases two or three single-phase transformers of different kVA ratings are connected as a three-phase transformer bank to provide three-phase service for critical customers. In these cases, the load division among transformers becomes unequal and results in an unbalanced distribution system. The results of this study corroborate power company experience. Even when both three-phase sources and loads of the bank are balanced, the load division among transformers is unequal if transformers of different capacities are used in a bank, or an open wye–open delta connection is adopted.     

Pedestrian Detection and Tracking Using a Mixture of View-Based Shape–Texture Models

This paper presents a robust multicue approach to the integrated detection and tracking of pedestrians in a cluttered urban environment. A novel spatiotemporal object representation is proposed, which combines a generative shape model and a discriminative texture classifier, both of which are composed of a mixture of pose-specific submodels. Shape is represented by a set of linear subspace models, which is an extension of point distribution models, with shape transitions being modeled by a first-order Markov process. Texture, i.e., the shape-normalized intensity pattern, is represented by a manifold that is implicitly delimited by a set of pattern classifiers, whereas texture transition is modeled by a random walk. Direct 3-D measurements that are provided by a stereo system are further incorporated into the observation density function. We employ a Bayesian framework based on particle filtering to achieve integrated object detection and tracking. Large-scale experiments that involve pedestrian detection and tracking from a moving vehicle demonstrate the benefit of the proposed approach.     

Design and Development of High-Power DC–DC Converter for Metro Vehicle System

This paper presents the design and development of a transformer isolated high-power dc–dc converter. There are several design issues and challenges. In this paper, we focus on three major issues in high-power dc–dc converters. 1) An energy recovery passive snubber circuit and the selection of pulsewidth modulation control methods are first introduced to reduce the voltage spike and power loss across switching devices. 2) Interleaved winding method is then employed to reduce proximity effect in the transformer winding. 3) The voltage oscillation problem in the secondary rectifier diode is addressed, and solutions are provided.