导电聚合物（PEDOT）浆料在钽电容器生产中应用

通过采用浸渍导电聚合物浆料和原位聚合方法制备聚合物钽电容器,并对比电容器电性能,研究导电聚合物浆料对聚合物钽电容器电性能的影响。实验结果表明导电聚合物浆料可以提高电容器的耐压性能,即产品有较高的击穿电压值,但是产品的容量引出率和ESR恶化。     

Metallized polymer film capacitors ageing law based on capacitance degradation

Passive components, particularly capacitors, are very used devices in power electronics applications providing key function on board. Nevertheless, capacitors breakdowns can have catastrophic consequences on the financial and human scale; a good acquaintance of their deterioration over time would contribute in the improvement of the availability of the whole system by performing a predictive maintenance on the component. This operation requires the knowledge of the capacitor ageing law and their failure mechanisms associated to the application. Capacitance loss can be mainly attributed to the self-healing process occurring in metallized film capacitors when used under high steady electrical and thermal stresses. In this paper, a capacitance ageing law is proposed based on the identification of voltage and temperature degradation kinetics from three experimental floating ageing tests performed at different voltage and temperature constraints. A total of 34 capacitors provided from different manufacturers using polyester film as dielectric have been studied and compared to validate the proposed law.     

高比容钽粉在电容器中的应用

优化了高比容钽阳极的烧结温度和压制密度,改进了氧化膜形成和被膜等工艺,最终解决了产品击穿电压低、阴极被膜不良等问题。产品的额定电压为4～16V、标称容量为10～100μF,各项指标均达到行业标准,成品合格率达到80%以上。产品容量约增加一倍、产品尺寸缩小一个壳号。     

Embedded thin film capacitors-theoretical limits

The large physical size of capacitors and/or excessive values of associated lead inductance are two major limitations in the development of novel packaging modules, with high packaging density, high performance and reliability along with low system cost. Embedded capacitor technology in thin film form offers a promising solution to these limitations. A design space with capacitance density and breakdown voltage as performance properties, with material dielectric constant and film thickness as parameters has been explored, focusing on tantalum pentoxide (Ta/sub 2/O/sub 5/) as the dielectric material. An inherent tradeoff is established between breakdown voltage and capacitance density for thin film capacitors. The validity of the proposed design space is illustrated with thin films of Ta/sub 2/O/sub 5/, showing deviation from the "best can achieve" breakdown voltage for films thinner than 0.4 /spl mu/m and films thicker than 1 /spl mu/m.     

导电高分子钽电解电容器的研究进展

综述了导电高分子钽电解电容器的最新研究进展。比较了导电高分子钽电解电容器和二氧化锰钽电解电容器在结构、制造工艺和性能方面的差别。还介绍了聚吡咯(PPy)、聚乙撑二氧噻吩(PEDOT)和聚苯胺(PANi)钽电解电容器的研究状况。导电高分子膜的形成工艺对钽电解电容器性能影响很大。改进和开发新型阴极材料是降低钽电解电容器等效串联电阻Res的重要途径。     

The maximum dielectric strength of thin silicon oxide films

Thin film silicon oxide capacitors with nonshorting breakdowns were investigated. Breakdowns appear in three forms: single hole, self-propagating, and maximum voltage breakdowns. Single hole and self-propagating breakdowns occur at flaws, and self-propagating breakdowns develop only when the resistor to the source is relatively small, less than 10 kΩ in these experiments. After flaws are burned out by single hole breakdowns, with larger source resistors the maximum voltage breakdown can be observed, destroying the whole capacitor simultaneously. Plotting current against voltage, the current increase is quasi-exponential, but prior to maximum voltage breakdown, the current continues to increase while the voltage decreases slightly below a maximum value Vm. Assuming thermal instability as the cause for this change in the I-V relationship, we have derived an expression for the maximum voltage Vm. Calculated results for fields up to 9.5 MV/cm were found to agree well with measurements for temperatures from -145°C to 65°C and for thicknesses from 3000 Å to 50 000 Å. Fmdecreases with increasing temperature and thickness of insulation, and is higher for silicon dioxide than for silicon monoxide films. Maximum voltage breakdown occurs when the quasi-exponential increase of leakage current with field produces thermal instability over the whole capacitor area. The maximum dielectric strength is characteristic of the whole capacitor and is determined by its electrical and thermal conductance.     

提高钽电容器可靠性的一种新老化方法

通过对钽电容器自愈机理的研究,针对传统老化方法不能彻底剔除电介质有缺陷的钽电容器的缺点,提出一种新的老化方法并对多种钽电容器进行老化实验。新方法可以有效识别并100%剔除电容器不良品,钽电容器生产率提高了50%,钽电容器失效率达到0.1%/(1 000 h),可靠性提高。经验证,这种新老化方法适用于固体电容器、片式钽电容器、聚合物钽电容器和液体钽电容器等多种元件的老化筛选。     

Ta2O5介质膜性能对液体钽电容器性能的影响

叙述了钽电解电容器阳极Ta2O5介质膜的形成过程,分析了电解液闪火与氧化膜击穿的微观过程。利用扫描电子显微镜(SEM)分析了阳极氧化后及产品失效后阳极钽芯表面介质膜的微观结构,并对液钽电容器失效机理进行了探讨。结果表明,介质膜内杂质或缺陷处O2-放电产生的电子发射是电解液闪火和氧化膜击穿的前驱点;在高电场或高温度的作用下,介质膜的场致晶化和热致晶化是液体钽电解电容器失效的主要模式。     

T pattern fuse construction in segment metallized film capacitors based on self-healing characteristics

The breakdown happens in metallized polypropylene film (MPPF) capacitor can be classified into two cases: the first one is self-healing, which means that the insulation will recover after the breakdown; the other one is self-healing failure, which means that the capacitor will fail because of short-circuit fault. In this paper, the MPPF capacitor applied in DC filtering which adopt the T pattern segment film technology is investigated. To simulate the two cases mentioned above, a model based on self-healing experiment data is built by Power Systems Computer Aided Design (PSCAD). The current density flowing through the fuse and fuse energy is calculated and analyzed. Meanwhile, the fuse burn-out criteria are investigated according to electrical explosion theory and phase transition energy of segment metallized film fuse. The fuse design methodology of T pattern segment film is presented and a design case is provided.     

组合式金属化聚酯膜电容器的研制

采用金属化聚酯膜、铝金属膜电极、无感式卷绕结构，研制成了ＣＬ２０１型组合式金属化聚酯膜电容器，其体积比箔式电容器要小１／２～２／３，比率电容量也相应提高了，并且电容器具有良好的自愈性。     

氧化膜强化技术在钽电容器生产中的应用

采用氧化膜强化技术在钽阳极体外表面形成抗机械应力的强化氧化膜,并模拟钽电容器回流焊过程,研究回流焊前后钽电容器漏电流变化以及对击穿电压(BDV)的影响。试验结果显示:在回流焊安装前后,应用氧化膜强化技术的电容器漏电流增幅小于普通产品14%;耐BDV比普通产品高6 V。     

Electrical characteristics of anodic tantalum pentoxide thin films under thermal stress

In this work, we report on electrical characteristics of tantalum oxide films fabricated by anodic oxidation of tantalum nitride and tantalum silicide with thicknesses ranging from 100 to 4500 Å. These films exhibit greatly improved leakage currents, breakdown voltage and a very low defect density, thus allowing the fabrication of large area capacitors. Leakage currents in the insulator under thermal stress have been carefully studied in order to determine the nature and physical origin of the dominant conduction mechanisms in the insulator. We have found noticeable differences in the dominant conduction mechanisms for thin and thick anodic tantalum pentoxide films. These differences are explained in terms of the thickness dependence of the insulator layer structure.     

Accelerated testing for failures of tantalum capacitors

This study focused on the use of accelerated testing to find out why tantalum capacitors fail. Stress effects of humidity, temperature, and ripple voltage were examined in different combinations. Results show that a standard 85/85 test with combined enhanced moisture and temperature does not result in failure of tantalum capacitors in 2500 h. However, with added ripple voltage, failures may occur in a relatively short time. High relative humidity and high temperature both affect water diffusion, but apparently increased ripple voltage in 85/85 testing causes tantalum capacitor characteristics to weaken and capacitors to fail. The paper elaborates on the possible reasons.     

Testing the effects of temperature cycling on tantalum capacitors

This study focused on the reliability testing of tantalum capacitors. The objective was to develop efficient tests to examine the effects of temperature cycling on capacitor maximum voltage. A test according to the standard JESD22-A104D overlooks the fact that temperature changes often occur while the voltage is on. Capacitors were first tested according to the standard without voltage; the test was then repeated with added 15 V and 30 V. Second, short cycling tests were run at different temperatures to detect any changes in capacitor characteristics. After the cycling tests, capacitors were tested for voltage, which was slowly increased from 0 V to 90 V, provided no failure occurred. Results suggest that a temperature cycling effect can be achieved in a much shorter time than in standard tests. Temperature cycling can also be accelerated by adding voltage. Possible reasons are discussed in the paper.     

High Density Double and Triple Layer Tantalum Pentoxide Decoupling Capacitors

High-performance integrated circuits (ICs) require extremely low impedance power distribution. The low voltage, high current requirements of these devices must be provided by decoupling capacitors very close to the IC. Currently this decoupling is provided by discrete surface mount capacitors with relatively high parasitic inductance, requiring many devices in parallel to provide low impedance at high frequencies. Thin film, large area tantalum pentoxide (TaO) dielectric capacitors exhibit very low parasitic inductance, but have been limited in capacitance density to 100nF/cm for single layer devices. Multilayer thin film capacitors can substantially increase the available capacitance. These multilayer thin film capacitors can be fabricated in a variety of ways, allowing them to be embedded between FR-4 layers, under ICs, or even embedded in IC packages. We previously described the initial results of two-layer capacitors fabricated on silicon . These devices had two dielectric layers and three copper plates. Recently we extended the technology to three dielectric layers, and fabricated devices with dielectrics as thin as 1000, to yield a total capacitance density of 0.6F/cm. Capacitors were fabricated on silicon wafers by sputtering a metal plate topped with tantalum, and then wet anodizing the tantalum layer. The process was repeated to create a multilayer stack. The stack was then patterned from top to bottom by successive lithographic and etching steps. This paper will describe the fabrication process in detail. Detailed electrical properties for the resulting two and three layer devices, such as capacitance density, leakage current, breakdown voltage, and impedance will be presented. Using the three-layer process, we fabricated devices for inclusion in a 3-D electronic assembly for a DARPA program, and these devices will be described. Screening and test methods to ensure device reliability will be briefly discussed.     

Lowering of the breakdown voltage of silicon dioxide by asperities and at spherical electrodes

The paper examines the assumption that asperites and corners in electrodes can be preferential sites for electrical breakdown of silicon dioxide capacitors. It was assumed for this purpose that asperities can be approximated by spherical surfaces, and the breakdown voltage was then calculated at such asperities. Calculations showed that the breakdown voltage of a planar silicon dioxide capacitor can be lowered by one half to two thirds by asperities, when their radius is less than about one half of the oxide thickness. Such a decrease in the breakdown voltage is widely observed in polysilicon oxide capacitors. The effect of asperities is alleviated by a trapped electron charge, which can increase the breakdown voltage significantly. The spherical asperity model accounted for the breakdown voltages observed on a wide range of polysilicon oxide capacitors with oxide thickness varying from 45 to 820 nm. The radius of asperities responsible for breakdown in these experiments was roughly estimated 25–35 nm.     

The effect of electrode material on the electrical conduction of metal-Pb(Zr0.53Ti0.47)O3-metal thin film capacitors

The electrical conduction of metal–PZT–metal thin-film capacitors depends on the electrode material due to the different magnitudes of the work functions. In this work, Au/PZT/Pt and Pt/PZT/Pt capacitors were fabricated and their electrical properties compared. At the low temperature range of 300–375 K, the electrical conduction of Au/PZT/Pt capacitor is space-charge-limited current (SCLC), whereas Pt/PZT/Pt capacitor shows ohmic conduction at low field (<0.55 MV/cm) and Frenkel–Poole emission at higher fields (0.55 MV/cm). The current level of Au/PZT/Pt is much lower than that of Pt/PZT/Pt at low field (<0.4 MV/cm) due to the larger barrier height for holes of Au/PZT. At high temperatures (375–450 K), the conduction mechanism of Au/PZT/Pt capacitor changes to Schottky emission, whereas that of Pt/PZT/Pt capacitor remains the same as in low temperatures of 300–375 K. The energy band diagrams of the Au/PZT/Pt and Pt/PZT/Pt systems are constructed to explain the different current–voltage characteristics.     

Optimization of Epoxy-Barium Titanate Nanocomposites for High Performance Embedded Capacitor Components

One of the most promising avenues to meet the requirements of higher performance, lower cost, and smaller size in electronic systems is the embedded capacitor technology. Polymer-ceramic nanocomposites can combine the low cost, low temperature processability of polymers with the desirable electrical and dielectric properties of ceramic fillers, and have been identified as the major dielectric materials for embedded capacitors. However, the demanding requirements of mechanical properties and reliability of embedded capacitor components restrict the maximum applicable filler loading (<50vol%) of nanocomposites and thereby limit their highest dielectric constants (<50) for real applications. In this paper, we present a study on the optimization of the epoxy-barium titanate nanocomposites in order to obtain high performance, reliable embedded capacitor components. To improve the reliability of polymer-ceramic nanocomposites at a high filler loading, the epoxy matrix was modified with a secondary rubberized epoxy, which formed isolated flexible domains (island) in the continuous primary epoxy phase (sea). The effects of sea-island structure on the thermal mechanical properties, adhesion, and thermal stress reliability of embedded capacitors were systematically evaluated. The optimized, rubberized nanocomposite formulations had a high dielectric constant above 50 and successfully passed the stringent thermal stress reliability test. A high breakdown voltage of 89MV/m and a low leakage current of about 1.9times10^-11A/cm² were measured in the large area thin film capacitors     

Impact of circuit resistance on the breakdown voltage of tantalum chip capacitors

Experiments are described in this paper whose results suggest a clear mathematical relationship between total circuit resistance (including the capacitor's ESR) and the voltage at which a capacitor is likely to break down. Specifically, the relationship defines how much each capacitor's (not precisely known) breakdown voltage is affected by changes in circuit resistance. Since a factor that strongly influences the reliability of a tantalum capacitor is the ratio of the capacitor's breakdown voltage to the applied voltage, if the impact of circuit resistance on breakdown voltage can be established, then, at least indirectly, the impact of circuit resistance on reliability can be inferred.The breakdown voltages of individual capacitors, drawn from large randomized samples, were determined for different values of circuit resistance. These data were analyzed and found to fit a specific mathematical relationship with a high degree of confidence. The relationship was found to hold for different, but similar, batches and part-types. The test methods employed to minimize statistical noise are described in the paper as is the resulting mathematical relationship. Implications of the relationship are explored and avenues of future research are suggested.     

Testing the effects of reflow on tantalum capacitors

This study focuses on testing the effects of one and several reflow processes on surface mount tantalum capacitor characteristics, especially in a humid environment. Effects on maximum voltage, moisture absorption, and durability in the standard 85/85 test were examined. Research was done by using a 0–90 V voltage test, a 100% RH moisture absorption test, and the standard 85/85 test. Results show that a reflow process weakens the characteristics of tantalum capacitors and also affects their moisture absorption. Several reflow processes have a greater effect. Possible reasons are discussed in this paper.