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The parallel-plate capacitor equation is widely used in contemporary material research for nanoscale applications and nanoelectronics. To apply this equation, flat and smooth electrodes are assumed for a capacitor. This essential assumption is often violated for thin-film capacitors because the formation of nanoscale roughness at the electrode interface is very probable for thin films grown via common deposition methods. In this work, we experimentally and theoretically show that the electrical capacitance of thin-film capacitors with realistic interface roughness is significantly larger than the value predicted by the parallel-plate capacitor equation. The degree of the deviation depends on the strength of the roughness, which is described by three roughness parameters for a self-affine fractal surface. By applying an extended parallel-plate capacitor equation that includes the roughness parameters of the electrode, we are able to calculate the excess capacitance of the electrode with weak roughness. Moreover, we introduce the roughness parameter limits for which the simple parallel-plate capacitor equation is sufficiently accurate for capacitors with one rough electrode. Our results imply that the interface roughness beyond the proposed limits cannot be dismissed unless the independence of the capacitance from the interface roughness is experimentally demonstrated. The practical protocols suggested in our work for the reliable use of the parallel-plate capacitor equation can be applied as general guidelines in various fields of interest.

Tantalum capacitors (TCs) are widely used in electronic appliances. The rapid replacement of electronic products results in generating large amounts of waste TCs (WTCs). WTCs, rich in valuable tantalum, are considered as high quality tantalum resources for recycling. However, environmental pollution will be caused if the organics of WTCs were not properly disposed. Therefore, effectively recycling the organics of WTCs is significant for recovering the valuable parts. This study proposed an argon (Ar) pyrolysis process to recycle the organics from WTCs. The organic decomposition kinetic was first analyzed by thermogravimetry. The results showed that the organics were decomposed in two major steps and the average activation energy was calculated to 234kJ/mol. Then, the suitable pyrolysis parameters were determined as 550°C, 30min and 100ml/min. The organics were effectively decomposed and converted to oils (mainly contained phenol homologs and benzene homologs) and gases (some hydrocarbon). These pyrolysis products could be reutilized as energy sources. Moreover, based on the products and bond energy theory, the pyrolysis mechanisms of the organics were also discussed. Finally, a reasonable technological process for products utilization was presented. This study contributes to the efficient recycling the organics before valuable material recovery from WTCs.

A solid state variable capacitor (SSVC) with minimum capacitor is proposed. A variable ac capacitor (with capacitance varied from 0 to $C_{{{\rm ac}}}$ ) is traditionally implemented by an H-bridge inverter and a large electrolytic dc capacitor, whose capacitance is 20 times of the ac capacitor's value, in order to absorb the ripple power pulsating at twice the line frequency (2 ω ripple power). The proposed SSVC system consists of an H-bridge and an additional phase leg connected to an ac capacitor with fixed capacitance $C_{{{\rm ac}}}$ and can reduce the dc capacitance to minimum value for absorbing switching ripples. The ac capacitor absorbs the 2 ω component and theoretically can eliminate 2 ω ripples to the dc capacitor completely. The total capacitor size is reduced by 13 times if same type capacitors (film) are used. Moreover, the proposed SSVC shows special advantages in terms of the switches’ current and voltage stress compared to other applications and the total device power rating is only 1.125 times of H-bridge. Since the proposed SSVC only has a small dc capacitor, a novel control system directly based on ripple power is also proposed to achieve stable dc voltage and fast dynamic response. Simulation and experimental results are shown to prove the effectiveness of the proposed SSVC with minimum capacitor.

High temperature and high electric field applications in tantalum and niobium capacitors are limited by the mechanism of ion migration and field crystallization in a tantalum or niobium pentoxide insulating layer. The study of leakage current (DCL) variation in time as a result of increasing temperature and electric field might provide information about the physical mechanism of degradation. The experiments were performed on tantalum and niobium oxide capacitors at temperatures of about 125°C and applied voltages ranging up to rated voltages of 35 V and 16 V for tantalum and niobium oxide capacitors, respectively. Homogeneous distribution of oxygen vacancies acting as positive ions within the pentoxide layer was assumed before the experiments. DCL vs. time characteristics at a fixed temperature have several phases. At the beginning of ageing the DCL increases exponentially with time. In this period ions in the insulating layer are being moved in the electric field by drift only. Due to that the concentration of ions near the cathode increases producing a positively charged region near the cathode. The electric field near the cathode increases and the potential barrier between the cathode and insulating layer decreases which results in increasing DCL. However, redistribution of positive ions in the insulator layer leads to creation of a ion concentration gradient which results in a gradual increase of the ion diffusion current in the direction opposite to the ion drift current component. The equilibrium between the two for a given temperature and electric field results in saturation of the leakage current value. DCL vs. time characteristics are described by the exponential stretched law. We found that during the initial part of ageing an exponent n = 1 applies. That corresponds to the ion drift motion only. After long-time application of the electric field at a high temperature the DCL vs. time characteristics are described by the exponential stretched law with an exponent n = 0.5. Here, the equilibrium between the ion drift and diffusion is achieved. The process of leakage current degradation is therefore partially reversible. When the external electric field is lowered, or the samples are shortened, the leakage current for a given voltage decreases with time and the DCL vs. time characteristics are described by the exponential stretched law with an exponent n = 0.5, thus the ion redistribution by diffusion becomes dominant.

Summary Circular economy approaches aim to close material cycles along the value chain. As such, the circular economy can be a long-term strategy to mitigate the risks of critical raw material (CRM) supply. Tantalum, with a current end-of-life recycling rate of less than 1%, has been intermittently discussed as critical. Even though the specificity of tantalum applications and high-mass fractions of tantalum in relevant components provide good boundary conditions, recycling barriers hinder the successful implementation of recycling technologies. With this case study, we identify potentials and barriers for implementing the recovery of CRM, using the example of tantalum. To this end, information about visually identifiable tantalum capacitors (VICs) and printed circuit boards (PCBs) in various equipment types was obtained by disassembly campaigns for mobile phones, smartphones, tablets, notebooks, desktop personal computers, flat screen monitors, servers, etc., and the chemical analyses of resulting fractions. Results show great differences in the application of tantalum in various equipment types. Because of this, the tantalum potential of put-on-market (POM) or of waste electric and electronic equipment (WEEE) devices differs between products and regions. Worldwide, the highest POM tantalum flows originate from desktop computers, but in Germany they originate from notebooks. A focus on particular products leads to higher yields in recycling and supports circular economy approaches. Recycling of tantalum from WEEE is generally possible. But an accurate separation of tantalum from PCBs is not feasible solely by separation of VICs. This process also leads to the loss of silver. Further, this study reveals potential miniaturization trends, decreasing the use of VICs, with an anticipated substitution of tantalum with niobium. These barriers impede long-term recycling strategies for tantalum aimed at establishing a circular economy.

Polymer aluminum (PA) electrolytic capacitors have solid conductive polymers as electrolyte. Reliability of polymer capacitors at elevated temperature humidity is not well understood. Elevated temperature–humidity testing was performed on PEDOT PA electrolytic capacitors by two manufacturers, Nichicon and Nippon Chemi-Con. Both the companies are among the top suppliers of aluminum electrolytic capacitors worldwide. Two different dominant failure modes of increase in equivalent series resistance and increase in leakage current (LC) were found in the PA capacitors from the two different capacitor manufacturers. The capacitance value of the polymer capacitors remained stable during the test. In the subsequent analysis, a new failure mechanism that has not been previously reported in the literature was found that leads to the high LC failure of PA electrolytic capacitors. The criteria for evaluation for this new failure mechanism should be included during the part and manufacturer selection process.

Recycling e-waste has been a significant topic for environmental protection and also for resource recovery. Waste tantalum capacitors (WTCs), widely existing in discarded small appliances, are rich in high quality tantalum (Ta) resources. However, recovering Ta from WTCs is difficult due to the tightly covered mold resin. This study proposes an efficient and environmentally friendly process using supercritical water (SCW) to decompose the organics and recover Ta from WTCs. Two methods of SCW were studied: SCW depolymerization (SCWD) and SCW oxidation (SCWO). The results indicated that the mold resin (packing) of WTCs were effectively decomposed by SCW treatments. The organic decomposition efficiency in SCWD was lower than that in SCWO. The optimal parameters for SCWD and SCWO were, respectively, considered to be 425 °C, 25 MPa, and 120 min and 400 °C, 25 MPa, and 90 min, adding a 10% volume ratio of H2O2. After SCWO treatment, Ta electrodes were directly recovered, and the purity of Ta could reach 93.18%....

Waste tantalum capacitors (WTCs), dismantled from waste printed circuit boards, are considered a high quality tantalum (Ta) resource. Ta is a rare and strategic material. Nearly half of the Ta consumption is used for manufacturing tantalum capacitors. Furthermore, large amounts of energy and chemicals are consumed during the Ta purification process. Therefore, recovering Ta from WTCs can sustainably utilize the Ta resource and reduce pollution. However, the recycling technology has been poorly developed. This study proposed vacuum pyrolysis (VP) and mechanical–physical separation (MPS) to recover Ta and other materials from WTCs. First, the WTCs were treated by VP to decompose the organics. The suitable VP parameters were considered as 400 °C, 50 Pa, and 60 min. Then, the residues were performed by MPS. Consequently, nickel–iron terminals were recovered by magnetic separation. Ta and silica were separated by corona electrostatic separation. The recovery rate and purity of Ta could reach 97.02 ± 0.85% and ...

The demand for tantalum (Ta) is rapidly increasing due to the manufacture of Ta capacitors (TCs) for electronic devices. With the increasing awareness of environmental protection and conservation of rare metal Ta, recycling of Ta from waste TCs (WTCs) is becoming a hot topic in current society. In this study, an efficient and environmentally friendly process for recycling Ta from WTCs by chloride metallurgy (CM) is proposed. In the CM process, the nontoxic FeCl2 is chosen as the chlorination agent. Thermodynamic analysis demonstrates that Ta can selectively react with FeCl2, and the generated TaCl5 can be easily separated and then condensed in the condensation zone. The recovery of Ta can reach 93.56% under the optimal chlorination parameters as follows: heating temperature of 500 °C, FeCl2 addition amount of 50%, holding time for 2 h, and particle size of Ta-rich powder less than 0.24 mm. Moreover, the kinetic mechanism is discussed, and the rate-controlling step in the chlorination reaction of Ta is det...

Highly-integrated 3D voltage regulators (IVRs) for high-power applications are developed for emerging applications such as AI computing and server. With this 3D process integration, passive components such as inductors and capacitors are embedded into substrates and placed close to the chips, resulting in short power delivery networks (PNDs) and high power efficiency. High-density tantalum capacitors are integrated with high-density magnetic-core inductors to realize IVRs with module thickness around 0.7 mm. By incorporating high-permeability magnetic materials as the cores, the inductors achieved 20X improvement in inductance as compared to air-core inductors. The high inductance allows inductors to be designed with less number of windings, resulting in low component resistance of 5 mΩ. The integrated components have package-compatible terminals that are compatible with electrolytic plating process. The terminals allow them to be connected with low-resistance vias to further reduce parasitic losses and improve the power efficiency. Short PDNs and low-resistance interconnections and low-resistance components make the demonstrated IVRs ideal for high-power density computing applications with high efficiency low-impedance power delivery networks.

I-V characterization of Ta-Ta2O5-MnO2 capacitors was investigated at different temperatures, and Poole–Frenkel (PF) emission saturation was experimentally observed. Under the saturation voltage, the I-V curves at different temperature converged, and the temperature dependency was vanished. Above the saturation voltage, the leakage current was decreasing as the temperature increased. In order to evaluate the effects of saturation voltages (VS) on time-to-failure (TTF) of the capacitors, VS were first determined at +2°C and +25°C, then voltage accelerating tests were conducted at 85°C under 1.6 times of rated voltage. The distribution of VS and TTF of the samples were plotted and compared. It was shown that samples with lower saturation voltage failed earlier in the distribution of time-dependent dielectric breakdown. Comparing conventional methods for evaluating the quality of tantalum capacitors by measuring the leakage current at elevated temperature, the nondestructive measurement of saturation voltage at +2°C and +25°C may provide a novel and practicing approach tool to screening out capacitors with defected Ta2O5 layers.

The reliability and failure modes in surface mount Solid Electrolytic and Polymer Tantalum capacitors were investigated using the parts manufactured with conventional technology and flawless technology (F-Tech) that suppresses typical defects such as crystalline inclusions in the amorphous matrix of the tantalum oxide dielectric. The accelerated tests were performed; failure rates were calculated based on the cumulative percent of failed parts vs time and acceleration factor. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy and thermo-gravimetric/deferential scanning calorimetry analysis (TGA/DSC) were included in the investigation to analyze chemical and structural transformations in the capacitors failed in the accelerated tests. Results show strong impact of technology on reliability and failure mode including the lowest failure rate and no wear-out failure mode in Polymer Tantalum capacitors manufactured with F-Tech. No ignition and burning tantalum were found in the Solid Electrolytic Tantalum capacitors that failed short. Limiting temperatures and protecting the encapsulating epoxy compound from ignition and burning at normal conditions of the accelerated testing take place via ablation process—heat consuming irreversible structural and chemical transformations in the material such as carbonization process.

The article is firstly focused on thermal analysis of electrolytic double layer capacitor (EDLC) operated at repeated cycles of charging and discharging. This process is mostly applied at switched mode power supplies (SMPS), where electrolytic capacitor within given period of operation acts as energy storage element (discharge period). Charging and discharging process of EDLC may cause additional heating, which consequently influences capacitor’s lifetime. This parameter (lifetime) is nowadays very important parameter of EDLC, because operational life of the most of complex power electronic systems is directly influenced by its most critical components, i.e., by electrolytic capacitors. In this paper, the theory necessary for capacitor analysis and analysis of heat transfer is presented. The particular aluminum electrolytic capacitor Nichicon is examined in the paper. The implementation of real model into COMSOL Multiphysics and consequent simulation settings are being described too. Based on the main parameters of target application, the simulation analysis is processed. These results are consequently verified by experimental measurements on a given sample of EDLC. Deviations between measured and simulated data are identified, and optimization steps for better accuracy are also given. Finally, the factors influencing the lifetime of electrolytic capacitors together with calculation of capacitor’s lifetime in power application are described. During lifetime estimation, heat transfer simulation modeling of capacitor is utilized. Presented approach offers acceleration of necessary variables identification, which are hardly to be identified with the use of measurements, e.g., capacitor’s core temperature. Thus, more accurate results regarding lifetime estimation can be achieved.

Aluminum electrolytic capacitors with polymer electrolytes were developed to obtain lower equivalent series resistance (ESR) than that is achievable with liquid electrolytes. Replacement of the liquid electrolyte with a solid conductive polymer also overcomes the propensity of the liquid to evaporate over time, which leads to a reduction in capacitance and an increase in ESR values. However, capacitor manufacturers acknowledge that humidity can degrade the polymer, thereby having an adverse effect on the reliability of polymer aluminum (PA) capacitors. In the current study, surface mount and thru-hole PA capacitors from two different manufacturers were subjected to highly accelerated stress testing (110 °C, 85% RH) and elevated temperature–humidity (85 °C, 85% RH) conditions for rapid assessment. The polymer electrolyte in the capacitors was poly(3,4-ethylenedioxythiophene). Failure analysis was performed to determine the observed failure modes and the underlying failure mechanisms. The dominant failure modes observed were an increase in leakage current and an increase in ESR.

This work focuses on a polymer based capacitive harvester which can be fabricated with help of roll-to-roll and low cost printing methods. In contrast to electrostatic MEMS based parallel plate transducers or dielectric elastomer systems here, the capacitance is varied as function of the mechanical load by changing of the top electrode area with help of an electrically conducting composite elastomer. In case of a composite elastomer electrode the maximum capacitance in compressed state does not only depend on the thickness and permitivity of the dielectric but first of all on the quality of the interface and the micro structure of the conducting phase in the composite electrode at the interface which was investigated by FEM Maxwell simulation. An equivalent circuit model is used to study the influence of the leakage current inside the dielectric and the bulk resistivity of the elastomer electrode. First experiments with state of the art polymer, thin film and novel printed dielectrics in contact with elastomer electrodes have been performed to prove the harvesting principle at low frequencies. Charges between 25 and 70 nAs per cm2 have been transferred per cycle at 100 V/200 V while the maximum capacity was between 0.4 and 0.8 nF/cm2.

When the valve metal is used as anode material, the dielectric properties of sol–gel-derived thin film are greatly enhanced. That is because anodized self-healing occurs at the interface of the anode and the thin film. An oxide insulating layer with a good dielectric property is generated. Anodization heals the defects and the breakdown spots of thin film. Other than anodized self-healing, electrode contact is also an important factor, affecting the dielectric characteristics of the thin film capacitor, which cannot be ignored, especially when both factors exist in one film device. In this study, the sol–gel-derived strontium titanate thin film is used as dielectric material in the film capacitor, and platinum and aluminum as electrode materials. We find that the Schottky barrier at the interface of platinum and strontium titanate greatly reduces the leakage current. However the interface barrier restricts the anodizing of aluminum electrode and the further enhancement of the dielectric strength of the thin film capacitor.

This paper describes active shunt LC decoupling circuit with ceramic capacitors, allowing volume reduction and lifetime improvement of the high-voltage dc filters. Active filtering is based on the energy exchange between high-voltage coupling and low-voltage auxiliary capacitors. The coupling capacitor enables use of the low-voltage switched-mode power stage and low-voltage auxiliary decoupling capacitor. Advantageously, this allows to reduce power dissipation, switching frequency ripple current, and to reduce volume of the circuit. Additionally, power efficiency and capacitor lifetime are improved by using recent high-voltage coupling multilayer ceramic capacitors, reaching very low ESR . This paper provides description of the active decoupling capacitor, and shows an example of the feedback control. Obtained performances are demonstrated on the prototype of 1300-μF/450-V capacitor, allowing to reduce volume by three, when compared to ordinary 450-V electrolytic capacitor.

Among all the raw materials for aluminum electrolytic capacitors, there is no doubt that the anode foil is one of the most important raw materials influencing the performance of capacitors. The voltage, capacitance, thickness and impurity content of the anode foil have a direct effect on the performance of capacitor. The cost of anodes also contributes to the total cost of capacitors by a high percentage. Thus, for the manufacturers of capacitors, minimizing the anode foil costs needs also to be taken into account besides its performance. Against such a background, this article evaluates the anode foil of a new supplier to be used in a 400 V medium and in a high voltage aluminum electrolytic capacitor with the purpose of minimizing the product costs while achieving the same performance. The capacitors with new supplier's anode foil are compared with that using the current anode foil by evaluating the performance by the change of the various electrical properties.

Submodule (SM) capacitor is a key component in a modular multilevel converter (MMC), the selection of which must consider the component’s specifications and the requirements of the targeted converter application. This paper focuses on the capacitor selection for MMCs in applications including high-voltage direct current (HVDC) transmission and static VAr compensation using metalized polypropylene film (MPPF) capacitors. The dominant ageing mechanisms of the MPPF capacitors are reviewed to define their operational limits. A straightforward computational procedure and a set of curves are presented to assist the capacitor selection, taking into account criteria in the aspects of maximum capacitor voltage, capacitor voltage ripple, SM voltage capability, and capacitor ripple current stress. Simulation shows the validity of the method and demonstrates its use in design examples.

Because of the fabricability of polymer and excellent dielectric properties of ceramics, ceramic-polymer composites have been investigated widely for embedded capacitors which can improve electric performance greatly. In order to obtain further application of composite, the embedded capacitors with three-layer sandwich structure containing the BaTiO3/epoxy composites as dielectric layer and copper foil as electrodes were fabricated. The dielectric properties are improved by preventing the defect in dielectric layer through lamination process. Our results show that the capacitors exhibit high dielectric permittivity (e = 20), low dielectric loss (0.01) at 103 Hz from 40 to 100 °C and high breakdown strength (24 kV/mm), which indicate that the lamination is a promising process for embedded capacitor fabrication and BaTiO3/epoxy composites have potential for high-performance embedded capacitors application in field of microelectronics.

The highly conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films were prepared on porous tantalum pentoxide surface as cathode for polymer tantalum capacitors (PTC). The electrical performances of PTC with PEDOT:PSS films as cathode were optimized by dimethyl sulfoxide (DMSO) bath treatment. With the DMSO-bath treatment of PTC, the equivalent series resistance (ESR) of PTC decreased from 25 mΩ to 9 mΩ. The ultralow ESR led to better capacitance-frequency performance. The device reliability investigation revealed the enhanced environmental stability of PTC. The enhanced performances were attributed to the conductivity improvement of PEDOT:PSS cathode films and the removal of excess PSS from PEDOT:PSS films.

In this study, the dielectric properties of metal-oxide-metal capacitors based on Tantalum Titanium Oxide (TiTaO) thin films deposited by reactive magnetron sputtering on aluminum bottom electrode are investigated. The structure of the films was characterized by Atomic Force Microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The dielectric properties of TiTaO thin films were studied by complex impedance spectroscopy over a wide frequency range (10 -2 - to 10 5 Hz) and temperatures in -50 °C to 325 °C range. The contributions of different phases, phases’ boundaries and conductivity effect were highlighted by Cole – Cole diagram (ɛ” versus ɛ’). Two relaxation processes have been identified in the electric modulus plot. A first relaxation process appears at low temperature with activation energy of 0.37 eV and it is related to the motion of Ti 4 + (Skanavi’s model). A second relaxation process at high temperature is related to Maxwell-Wagner-Sillars relaxation with activation energy of 0.41 eV.

We report that efficient high dielectric polymer/ceramic composite materials can be optically printed into three-dimensional (3D) capacitor by the projection based stereolithography (SLA) method. Surface decoration of Ag on Pb(Zr,Ti)O 3 (PZT@Ag) particles were used as filler to enhance the dielectric permittivity. Polymer nanocomposites were fabricated by incorporating PZT@Ag particles into the photocurable polymer solutions, followed by exposure to the digitally controlled optical masks to generate 3D structures. The dielectric permittivity of Flex/PZT@Ag composite reaches as high as 120 at 100 Hz with 18 vol% filler, which is about 30 times higher than that of pure Flex. Furthermore, the dielectric loss is as low as 0.028 at 100 Hz. The results are in good agreement with the effective medium theory (EMT) model. The calculated specific capacitance of our 3D printed capacitor is about 63 F g −1 at the current density of 0.5 A g −1 . Cyclic voltammetry (CV) curves indicate 3D printed capacitors possess low resistance and ideal capacitive properties. These results not only provide a tool to fabricate capacitor with complex shapes but lay the groundwork for creating highly efficient polymer-based composites via 3D printing method for electronic applications.

The first article in this series [1] covered the early history of electrolytic capacitors, from their invention around 1880 to the invention of the modern Al electrolytic capacitor structure in 1925. The second article [2] takes us from Samuel Ruben’s 1925 invention to the wide range of Al electrolytic capacitors presently on the market. The present article discusses electrolytic capacitors based on metals other than Al.

The study to obtain tantalum concentration from electronic components (ECs) on Printed circuit board assembly (PCBA) of laptop was conducted. Electronic components on laptop PCBA were detached from boards by using self-developed experimental apparatus. The detached electronic components were sieved and 93.2 wt.% of tantalum capacitors were concentrated from the size interval from 2.80 mm to 6.35 mm. The tantalum capacitors were pulverized by hammer mill and electrodes (anode and cathode) were removed from the grinding products by using magnetic separators under the magnetic force of 300 Gauss. Finally, tantalum concentrate was concentrated from the magnetic separator products by using Knelson concentrator, and the maximum efficiency of 76.9% was achieved under the operating condition of bowl rotating speed of 200 rpm, and fluidizing water flowrate of 7 L/min. The grade and recovery of Ta concentrate under the condition were 81.1% and 78.8%, respectively.

Electrochemical capacitors are becoming promising energy conversion/storage and power output devices. However, high cost and low energy density are two serious disadvantages. By integrating the advantages of Li-/Na-ion batteries and electrochemical capacitors, Li-/Na-ion capacitors have been explored recently. Al is very cheap and is the most abundant metal element on the earth. There are few reports on Al-ion capacitors due to the challenges in finding a suitable anode with large capacitance and good rate performance. Here, the feasibility of assembling an Al-ion capacitor with good electrochemical performance is demonstrated. The Al-ion capacitor is assembled by using a composite of MoO3 nanotubes coated by a conductive polypyrrole (PPy@MoO3) as an anode, which functions via a redox intercalation/deintercalation of Al3+ ions in aqueous solution. It delivers a capacitance of 693 F g−1, about 3 times higher than that of electrode materials for sodium-ion capacitors in aqueous solution. Combined with an activated carbon (AC) cathode, the Al-ion capacitor presents an energy density of 30 W h kg−1 and an excellent cycling life with 93% capacitance retention after 1800 cycles. This finding provides another energy storage device with low cost and promotes the application of capacitors.

As new temperature critical applications continue to emerge, the need for components capable of enduring temperatures up to and exceeding 200°C is increasing. Advanced down-hole electronics, underhood automotive and aerospace systems rely on components delivering optimal performance while subject to extreme environmental conditions. This paper will discuss the design advances in tantalum technology that have given rise to innovative devices that provide the enabling technology for a new generation of applications. Traditionally, hermetically sealed “wet” axial tantalum capacitors (utilizing a non-solid electrolyte that promotes self-healing and long lifetime), have been used for both high bulk capacitance (to 5,600uF) and high voltage applications (to 125VDC). In recent years, this technology has been developed to meet the 200°C operational requirements of harsher environment industrial applications. For lower operating voltages (6v – 25v), SMD packages are preferred, and for several years, 200°C rated high temperature solid tantalum chip devices have been the preferred technology over “wet” tantalum for capacitances to 220uF, being smaller size, lower cost and having the combination of lower ESR and higher frequency response. More recently, hermetic SMD packaging has been developed for SMD solid tantalum capacitors. The hermetic seal enables the internal element to be operated in an inert gas environment, while offering superior resistance to moisture ingress. These two factors enable operation to 230°C, with higher capacitance (up to 330uF) and voltage (up to 63vDC) ranges. Both molded and hermetic high temperature SMD solid tantalum capacitors have been developed to be compatible with high temperature pcb or hybrid circuit assembly processes, with a range of termination finishes compatible with HMP solder, epoxy or wire bonding. Their design also harsh mechanical environment shock & vibration. This paper will discuss the evolution in materials, design and testing for each of these technologies, along with the considerations taken into account to give maximum compatibility with emerging requirements in high temperature and harsh environment applications, with emphasis on down-hole oil exploration, aerospace and military systems and underhood automotive electronics.

Emerging power electronics in a broad range of military, aerospace, hybrid vehicle, renewable energy and drilling applications rely on advances in dielectric materials for capacitors. Compact capacitors possessing low dielectric loss and high operating temperature capability are needed for power conditioning in advanced converter and inverter designs for these applications. Wound film capacitors represent the preferred capacitor technology but are limited by low operating temperature capabilities, < 150°C, and low volumetric efficiency, capacitance per unit volume less than 1.0 μF/cc. TPL is developing processes and manufacturing techniques for fabrication of advanced capacitor films comprised of high temperature polymers modified with ceramic nanoparticles. The selected polymers enable high temperature operation and the ceramic nanoparticles enhance volumetric efficiency by increasing the dielectric constant. The fabricated films are adaptable to conventional wound film capacitor construction methodologies. This paper provides an overview of TPL's experience to-date with a film dielectric material system comprised of fluorenone polyester polymer and titanate nanoparticle filler. The fluorenone polyester polymer was selected to provide a stable operating temperature of at least 200°C, while the addition of the titanate powder increases the dielectric constant and, in turn, the volumetric efficiency of wound film capacitors constructed with this film system. Status and ongoing capacitor development issues are provided relative to the intended high temperature power conditioning applications.

This paper covers technological results achieved with silicon capacitors for Aerospace applications, including stability, reliability and frequency data at high temperatures, as well as thermal stress, vibration & shock tests and radiations stress, according to ESA TRP reference (n° T723-325QT).

For applications such as electronics for down-hole drilling and exploration, geothermal energy generation and power electronics, there is a growing need for capacitors that have robust reliability at temperatures of 150°C or above. Conventional X7R and X8R type ceramic capacitors are designed for applications up to 125°C and 150°C, respectively. At temperatures above 150°C, these types of capacitors typically suffer from degradation of reliability performance and severe reduction in capacitance, especially under DC bias conditions. A Class-I C0G dielectric has been developed using Nickel electrodes for high temperature application up to 200°C and beyond. Due to its linear dielectric nature, this material exhibits highly stable capacitance as a function of temperature and voltage. Multi-layer ceramic capacitors (MLCC) made from this material can be qualified as X9G with robust reliability. These C0G capacitors are showing robust reliability at extreme temperature of 260°C (500 degrees Fahrenheit). We have also developed a modified-X7R dielectric composition with nickel internal electrodes showing high reliability in this Class-II dielectric at 175°C. This paper will report electrical properties and reliability test data on these Class-I C0G and Class-II ceramic capacitors at high temperatures of 150–200°C and above.

Waste tantalum capacitors, containing about 30–40 wt% rare metal tantalum (Ta), are one of the main Ta secondary resources. Not just to achieve the Ta resource recovery but to realize the value-added utilization, we recycled waste tantalum capacitors to prepare Ta2O5 photocatalyst by a chlorination-sintering process. To enhance the photocatalytic performance, Ta2O5 was further decorated by polyaniline (PANI) through a chemisorption approach. The as-prepared Ta2O5 and Ta2O5/PANI photocatalysts exhibited irregular nanoparticles with the particle size of 50–80 nm. After the PANI decoration, the photocatalytic performance of Ta2O5 was significantly enhanced. The optimal simulated sunlight H2 evolution rate and RhB degradation rate constant of Ta2O5/PANI (3 wt%) could reach 200.8 μmolg−1h−1 and 0.1342 min−1, which were about 3.3 and 5.6 times higher than those of Ta2O5. The superior photocatalytic performance of Ta2O5/PANI was ascribed to the intense interfacial interaction, increased visible light absorption and efficient charge carrier separation. In short, this study demonstrates a sustainable approach to convert e-waste to high-value-added and high-efficient photocatalyst, which is significant for waste utilization and environmental protection.

Stability of Polymer Tantalum capacitors with pre-polymerized PEDOT (slurry PEDOT) cathodes were investigated under different environmental conditions. Capacitance dependence on temperature, frequency, and dc bias voltage were investigated in humid and dry capacitors with different dielectric thicknesses. Electrical measurements and scanning electron microscopy (SEM) were used to characterize the capacitors. Humid capacitors were observed to have higher capacitance than dry capacitors for all dielectric thicknesses. The capacitance for all dielectric thicknesses was observed to increase with temperature in both humid and dry capacitors. Humid capacitors showed a strong temperature dependence at lower temperatures while dry capacitors showed a strong temperature dependence at higher temperatures. These temperature effects were more pronounced in thinner dielectric capacitors, and the results were explained by the integrity of the dielectric-polymer interface. The capacitance for all dielectric thicknesses was also observed to decrease with an increase in frequency, both in humid and dry capacitors. The frequency effect was more pronounced in humid capacitors with thinner dielectrics. These results were explained by a distributed capacitance model, secondary transitions of the polar segments of the polymer cathode, and lower reactance and lower self-resonance frequency of the thinner dielectric capacitors. The technological principles of improving environmental stability of Polymer Tantalum capacitors are also discussed.

Tantalum (Ta) is the one of the most critical elements according to the European Commission. Research on tantalum recovery from secondary sources such as waste electrical and electronic equipment (WEEE), bottom ash and by products of the industrial activities, however, is limited. In this study, the recovery potential of tantalum from spent tantalum capacitors was tested using bioleaching. Three different kinds of microorganisms were tested for tantalum recovery, which were Pseudomonas putida (DSM No. 6125), Bacillus subtilis (DSM No. 1088532), and Penicillium simplicissimum (DSM No. 1078). It turned out that P. simplicissimum has the ability to leach tantalum from wasted tantalum capacitors with a maximium leaching rate of 1.25 g Ta per kg sample. An unknown species achieved the highest leaching rate (9.88 g Ta / kg sample) but isolation and identification failed. The potential of tantalum recovery by bioleaching is demonstrated, however, further research needs to be carried out.

Gamma radiation induces surface defects in PEDOT which could recover under electric field, where gamma ray restricts the polarization of dipole. Parameters of PEDOT tantalum capacitor in space could be stable when resting and vary less when working. Gamma ray favors the use of PEDOT cathode tantalum capacitor in space.

Experimental research was carried out under the stimulation of 10 μF tantalum capacitor discharge, to obtain the ignition characteristics of micro-energy semiconductor bridges (SCB) with different ignition compositions. Meanwhile, the critical ignition voltages of different pyrotechnics were tested by the Neyer-D optimal sensitivity test method. The results reveal that SCBs with multiple ignition compositions are entirely different in ignition voltage and current signal. These five kinds of pyrotechnics in ascending order of firing sensitivity are: refined lead styphnate, neutral lead styphnate, basic lead styphnate, zirconium/potassium chlorate, and lastly lead azide, while lead ferrocyanide/potassium perchlorate and boron/potassium nitrate are relatively insensitive to SCB.

Several studies on the degradation mechanism of electrochemical capacitors have been conducted, but they have not predicted and analyzed the lifetime of the capacitors. A capacitor's life is normally considered to end when its capacity is reduced to 20% of the initial level or its ac equivalent series resistance (ESR) increases by 200% compared its initial value. Once the ac ESR reaches a failure state, it becomes impractical to use it as a factor to determine the failure of an electrochemical capacitor; hence, only the capacity is considered as a factor when determining a capacitor's failure. This method, which is used for small-scale electrochemical capacitors employed as capacitance backup, cannot be applied to new electrochemical capacitors with high output and low resistance. Therefore, we analyzed a failure mechanism by conducting a load-life test on high-output cylindrical-shaped electrochemical capacitors under different voltages (2.5, 2.7, and 2.9 V) and temperatures (333.15 K, 343.15 K, and 353.15 K) for 1000–1500 h, using the simulation software ALTA 8 PRO and Weibull ++8. By proposing an appropriate dc ESR as a life-determining factor for existing capacitors and by analyzing different failure conditions (150%, 180%, and 200%) through comparison, we found that a 180% increase in the dc ESR over its initial level is the most appropriate factor to be used as a failure condition for electrochemical capacitor performance. In addition, in the case of performance degradation due to voltage and temperature changes, an acceleration factor for each condition has been deduced, facilitating a preliminary performance evaluation w an accelerated life test.

Despite being highly reliable under steady state operating conditions, manganese dioxide (MnO2) tantalum capacitors are prone to catastrophic exothermic failures under surge current conditions. Such failures can be mitigated by the use of conductive polymers in place of MnO2. However, these polymers are more susceptible to failure at elevated humidity levels. In this paper, the electrical performances of both MnO2 and polymer tantalum capacitors are compared by subjecting them to temperature humidity bias testing at 85°C and 85% RH. The test population consists of tantalum capacitors with two voltage ratings (50V and 16V). At each of these voltage ratings, two sets of tantalum capacitors, one each with MnO2 and conductive polymer electrodes, were tested. The voltage levels used to bias the capacitors were periodically increased in multiples of the rated voltage to accelerate degradation. The performance of the capacitors was tracked by monitoring their capacitance, dissipation factors and leakage currents, both in-situ and at room temperature. The degradation trends are discussed in light of the differences in voltage ratings and electrode types. These trends are also mapped to fundamental failure mechanisms within the capacitors.

Energy-efficient residential lighting such as household light-emitting diode (LED) lamps with ac input require an ac/dc converter (or driver) with large output capacitance to minimize the low frequency LED current ripple. The energy storage capacitor used in the conventional ac/dc LED driver is usually an electrolytic capacitor due to its low cost and high energy density. However, the average lifetime of an electrolytic capacitor is at least 2–3 times less than that of an LED device. Hence, the potential lifetime of the LED lamp is significantly affected by the presence of the electrolytic capacitor in the driver circuit. In this paper, two novel isolated single-switch ac/dc high power factor LED drivers without using any electrolytic capacitors are proposed. In the proposed circuits, the energy storage capacitor is moved to the rectifier side, with a three-winding transformer used to provide isolation; input power factor correction as well as to store and provide the required energy to the output. As a result, the energy storage capacitance is significantly reduced, which allows film capacitor to be used to replace the conventionally used electrolytic capacitors. The circuit’s operating principles and its characteristics are described in this paper. Simulation and experimental results are given on a 120 $\text{V}_{\rm rms}$ , 12 W prototype to confirm that a power factor of at least 0.96 is achieved.

The operating temperature of a power capacitor has an effect on its service life directly. A 500-kvar power capacitor is taken as the research object. The capacitor fever produced by internal dielectric loss is considered under the running condition of 55 $^{\circ}\hbox{C} $ . The 3-D finite volume method calculation model of capacitor temperature is established, and the temperature distribution characteristics and the internal temperature at the hottest spot of the capacitor are obtained. With the research on a corresponding prototype, the numerical simulation results are consistent with the test values. The accuracy of temperature calculation model is testified, which provides a reliable basis for the design and operation of power capacitor.

Metallic niobium powder was produced for applications in electric capacitors via calciothermic reduction of niobium hydroxide in molten CaCl 2 . Sub-micrometer spherical metallic particles with coral-like morphologies reflected the particle size of the starting oxide powder. A fine powder was obtained from the mixtures of niobium hydroxide and CaO or Ca(OH) 2 , respectively. Sintered pellets of the metallic powder showed a higher capacitance (CV) than those of the simply reduced powder without pre-treatment, because the shrinkage during sintering was smaller. The CV was as large as that of commercially sintered pellets for tantalum capacitors. Therefore, this niobium powder would act as a higher-voltage capacitor by applying chemical anodic treatment at higher voltages, and lower oxygen content in the reduced power could realize a lower leak current.

This paper presents a new structure for the Micro-electromechanical capacitors with high capacitance and tuning range. The obvious feature of the proposed capacitor is the use of a thermal actuator to change the dielectric coefficient of capacitor. In this work, BaTiO3 is used as a dielectric. Due to its high dielectric coefficient, BaTiO3 increases the capacitance in this structure. Another characteristic of this material is that it changes the dielectric coefficient linearly in a specified temperature range. Through this work, given the thermal properties of the dielectric, a variable capacitor with a wide tuning range is made using a heater as a thermal actuator. The proposed variable capacitor has a one-piece structure and removes problems such as the pull-in effects completely by eliminating the moving parts. The results show that the tuning range of the proposed capacitor is about 600 % and its capacitance density is equal to 41.66 μF cm?2. This capacitor can be used in the MEMS telecommunication systems, particularly radars that require high capacity with too small sizes.

High-voltage high-current pulse power sources such as linear transformer driver, Marx generator and magnetically driven flyer device require that the capacitors have a long life and high reliability. To meet requirements, life tests of five capacitors which have been used in pulse power systems were carried out. A capacitor test facility capable of ~3,000 shots/month, which is a portable high-voltage test facility designed primarily for testing high voltage capacitor that may be used in future, has been designed and operated. This paper summarizes the results of our lifetime testing of the selected five kinds of high energy storage low inductance capacitors. Different combinations of insulating mediums (polypropylene film and high quality capacitor paper) and impregnating agents (benzyl toluene and castor oil) were studied in order to optimize the structure of capacitors and improve performance of capacitors in future. The effects of high reversal on the lifetimes of capacitor for given insulating medium and impregnating agent show that the selected insulating medium and impregnating agent are suitable for capacitor working under high reversal. The life test data which shows that the design of these capacitors is successful may be combined to estimate the reliability of pulse power sources in the future. These work and results may give us some guidelines to design and apply a capacitor.

The size of pores and throats is at the nanometer scale in tight oil and shale gas zones, and the resistivity of these reservoirs is very high, so the reservoirs show more dielectric properties than conductivity properties. The conductive and dielectric characteristics of a parallel plate capacitor full of fresh water, NaCl solutions, and solid dielectrics, for example, sands are investigated in this paper, and the capacitance data of the non-gas capacitor are measured at different salinities and frequencies by a spectrum analyzer. The experimental results illustrate that the capacitance of this kind of capacitor is directly proportional to the salinity of the solutions and inversely proportional to the measuring frequency, the same as a vacuum parallel plate capacitor. The remarkable phenomenon, however, is that the capacitance is inversely proportional to the square of the distance between two plates. The specific characteristic of this capacitor is different from the conventional parallel plate capacitor. In order to explain this phenomenon, the paper proposed a new concept, named “single micro ion capacitor”, and established a novel model to describe the characteristics of this particular capacitor. Based on this new model, the theoretical capacitance value of the single micro ion capacitor is calculated, and its polarization and relaxation mechanisms are analyzed.