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Due to the importance of capacitance temperature stability in precise analog circuit applications, capacitance instability at elevated temperature of 125°C was investigated in tantalum capacitors with PEDOT:PSS counter electrodes. Capacitance-voltage measurement supposed that residual ions in the PEDOT:PSS dispersion caused an accumulation of charges at the dielectric-cathode interface which contributed to an increase in the dielectric constant and resulted in the capacitance increasing at high temperature. Based on the hypothesis, water wash process was applied and capacitance dropped significantly at high temperature. This study shows that an additional water wash process is necessary to improve the capacitance temperature stability after each dispersion dip step.

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 replacement of the anode material in tantalum capacitors by a new generation of high CV niobium powders offers the possibility to get an economical alternative to tantalum for a wide range of applications. Due to the high CV potential of niobium powder there is also an alternative to low voltage aluminum electrolytic capacitors. We developed a new niobium capacitor which shows stable electrical values. By optimizing the structure of the dielectric and the cathodic layers as well as the process parameters we gained a capacitor which can be used up to105 °C. Electrical characteristics and lifetest behavior of niobium capacitors out of 100 k–150 k CV/g powder will be discussed.

Solid electrolyte tantalum capacitors (Ta) are a major part of the passive electronic components industry. These capacitors are comprised of a sintered porous Ta powder compact on which a dielectric film of tantalum pentoxide (Ta2O5) is grown electrochemically. In most cases, a conducting MnO2 counter-electrode is applied by pyrolysis of an aqueous solution of Mn(NO3)2. Such capacitors have very high volumetric efficiency and excellent long-term stability. However, in certain applications, some of the tantalum properties are not required. This has led to the development of high efficiency ceramic capacitors and organic semiconductor aluminum capacitors that can substitute for Ta in some applications. Another potential substitute material is niobium (Nb), which has electrical and chemical properties similar to tantalum. Early attempts to use Nb failed because of an unstable niobium=niobium pentoxide (Nb2O5) interface [1], but recently two approaches to stabilization have been developed. One is based on the known effect of Ta nitriding, and the other takes advantage of the unique properties of niobium monoxide (NbO). This paper discusses the dynamics of the substrate=dielectric interface and shows how control of oxygen migration at the interface results in improved capacitor performance.

With the dramatic growth in electronic circuitry applications, more demands are being placed on those systems’ integrity and reliability. More circuits require use of higher frequencies and smaller space to miniaturise products. The next generation microprocessors require lower voltages and increased supply currents. Over the past 3, 5 years, microprocessor current has increased 5 times and equivalent series resistance (ESR) requirements have dropped by a factor 7. Therefore, capacitors must have high capacitance and low ESR [1]. Tantalum capacitor manufacturers have been developing novel technologies such as new anode design & process optimisation in order to achieve the lowest possible ESR [2–7]. Conductive silver adhesives used for bonding the tantalum anodes onto the leadframe have an impact on both the electrical and mechanical performance. As a supplier of such adhesives, Emerson & Cuming conducted a research program in order to identify and develop silver adhesives combining a very high throughput with excellent electrical and mechanical performance. This paper investigates the effect of different adhesives combined with different leadframe metallisations on the ESR and the mechanical strength. The effect of the cure schedule has also been investigated. It is concluded that the selection of a conductive silver adhesive depends on the metallisation of the leadframe and the preferred cure method.

The possibility of enhancing the frequency performance of electrochemical capacitors by tailoring the nanostructure of the carbon electrode to increase electrolyte permeability is demonstrated. Highly porous, vertically oriented carbon electrodes which are in direct electrical contact with the metallic current collector are produced via MPECVD growth on metal foils. The resulting structure has a capacitance and frequency performance between that of an electrolytic capacitor and an electrochemical capacitor. Fully packaged devices are produced on Ni and Cu current collectors and performance compared to state-of-the-art electrochemical capacitors and electrolytic capacitors. The extension of capacitive behavior to the AC regime (~100 Hz) opens up an avenue for a number of new applications where physical volume of the capacitor may be significantly reduced.

The goal of this research was to test the effects of seacoast atmosphere on tantalum capacitors. Four tests were chosen for this purpose: the 85/85 test was chosen for testing the effects of the combination of high humidity and high temperature, salt spray testing was done for examining the effects of high humidity and salt, temperature cycling test was applied for testing the effects of temperature changes, and a 100% RH humidity test was developed for examining the effects of very high humidity. The results show that combination of high humidity and high temperature did not possess a significant risk for these capacitors during their normal use. Very high humidity and radical temperature changes both affected the breakdown voltages of tantalum capacitors. Salt fog caused corrosion of these components and had a small effect on breakdown voltage but did not have an effect on capacitance or ESR.

The analysis of electrolytic capacitors as a distributed network is examined. The parameters contributing to the equivalent series resistance (E.S.R.) have been determined for various production capacitors at low and high frequencies.

This paper shows the type of development that has occurred over recent years in tantalum capacitors, with particular reference to the sintered tantalum powder – liquid electrolyte (wet Ta) system. In the ‘wet’ system, the various defects that arise, such as silver migration, scintillation and field crystallisation, are illustrated and the effect of improvement in initial particle shapes on final surface area is considered.

The wet tantalum capacitor is well established in both power supply smoothing and timing applications and has a well proven high reliability. This paper reviews the mechanisms of the possible failures arising from mis-application or over-stressing. The effect of over voltage on the anodic oxide is considered and the influence of cathode structure on reverse voltage and ripple current capability is discussed. The silver cathode allows migration of silver ions through the electrolyte under appropriate conditions and hence produces a failure mechanism not present in the tantalum cathode device. The life of a wet tantalum unit is eventually limited by loss of water vapour leading to open-circuit. Results are presented for button style capacitors which suggest that this is in fact not a practical limitation.

It has been suggested that failure of solid tantalum capacitors is due to thermal migration of impurities from the tantalum anode to flaws in the oxide layer. This implies, however, that leakage current gradually increases under normal operating conditions, an effect which has not been observed. An alternative hypothesis advanced here is that failure is due to crystallization of tantalum oxide under the influence of the electric field. Scanning electron microscopy of specially cleaned anodized tantalum sheet on which thin gold electrodes have been deposited clearly shows the occurrence of crystallization after 17 hours at an applied voltage of 75 V and a temperature of 65℃. Results of accelerated life tests on solid tantalum capacitors at temperatures of 85℃ and 125℃, and at up to 2,5 times rated voltage also accord better with a field crystallization hypothesis than with a thermal migration failure hypothesis.

The electrical characteristics of anodic oxide films formed on tantalum are investigated in anodes oxidized in the standard electrolytes for low-voltage (0.01% H3PO4in water) and high-voltage (same plus ethylene glycol) applications. It is found that small additions (about 0.1%) of certain organic acids such as citric acid to the above electrolytes greatly improves the leakage current, the scintillation voltage and the dielectric losses of tantalum capacitors. Furthermore, the use of these organic acids makes it possible to extend to higher voltages the use of the low-voltage electrolyte, and allows, in the case of the high-voltage electrolyte, a substantial diminution in the ethylene glycol concentration without impairing the characteristics of the resulting capacitors. Finally, the effect of the citric acid and the ethylene glycol in the anodizing electrolytes is discussed.

Noise has been measured in a number of biased solid tantalum capacitors at frequencies down to 0.01 Hz. The noise current was found to have a 1/f power spectrum, and the amplitude varied with the bias voltage with a law in the range 1st to 4th power. There was a large difference in amplitudes between different capacitors of the same type.

The ripple current rating in electrolytic capacitors is limited by the maximum allowable temperature rise inside the capacitor. The temperature rise is determined by the I2R losses inside the capacitor and the efficiency of heat flow from the interior to the surrounding. The ripple current rating can be extended by either reducing the tanδof the capacitor or by increasing the efficiency of heat flow to ambient.The heat flow is determined by the thermal characteristics of the capacitor surface and thermal conductivity of the medium separating the capacitor winding from the surrounding.In this article a mathematical analysis for the heat flow in capacitors is given. The effects of various parameters are examined and methods of extending the ripple current rating are discussed.