Capacitance Stability of Polymer Tantalum Capacitors Under Different Environmental Conditions

Polymer Hermetic Sealed (PHS) Tantalum capacitors with pre-polymerized PEDOT cathodes and different dielectric thicknesses were used to study the stability of Polymer Tantalum capacitors under different environmental conditions. In particular, capacitance dependence on temperature, frequency, and dc bias voltage were studied in humid and dry capacitors with varying dielectric thicknesses. Capacitance and ESR measurements were performed 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 stronger temperature dependence at lower temperatures while dry capacitors showed a stronger 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 the RC ladder effect, secondary transitions of the polar segments of the polymer cathode, and lower reactance and lower self-resonance frequency of the thinner dielectric capacitors

The tantalum-cased tantalum capacitor

Tantalum-cased tantalum capacitors were tested with regard to temperature stability, capacitance ratio, surge current capabilities, shock, vibration, and thermal shock. They were found to be superior to the conventional wet slug tantalum capacitor cased in silver, since they are more resistant to sulfuric acid. The tantalum-cased tantalum capacitors are widely accepted for use in critical electronic equipment because of their excellent performance and reliability

Radiation effects design handbook. Section 3 - Electrical insulating materials and capacitors

Steady state radiation effects on electrical insulating materials and capacitors - handboo

Reliability studies on solid tantalum electrolytic capacitors

The primary objective of this thesis is to determine and analyze the failure mechanisms of solid tantalum capacitors, pinpoint the causes, and suggest the precautionary measures that prevent the occurrence of these failures. To achieve this goal, the study went in two directions, theoretical and experimental. The theoretical part-is a comprehensive review of the work -done on tantalum capacitors since 1960 up to date. The experimental part of the study is a life test (1000 hours) of solid tantalum capacitors under humidity and high temperature. To avoid the misconception that could happen by investigating a particular manufacturer\u27s product, units from five international companies are tested. For each unit, three parameters are measured before and after the life test; namely capacitance, equivalent series resistance (ESR), and leakage current. Both humidity and temperature were found to have profound effects on capacitor behaviour. The study was also able to rank the five major capacitor producers according to their units behaviour before and after the life test

Leakage Currents and Gas Generation in Advanced Wet Tantalum Capacitors

Currently, military grade, established reliability wet tantalum capacitors are among the most reliable parts used for space applications. This has been achieved over the years by extensive testing and improvements in design and materials. However, a rapid insertion of new types of advanced, high volumetric efficiency capacitors in space systems without proper testing and analysis of degradation mechanisms might increase risks of failures. The specifics of leakage currents in wet electrolytic capacitors is that the conduction process is associated with electrolysis of electrolyte and gas generation resulting in building up of internal gas pressure in the parts. The risk associated with excessive leakage currents and increased pressure is greater for high value advanced wet tantalum capacitors, but it has not been properly evaluated yet. In this work, in Part I, leakages currents in various types of tantalum capacitors have been analyzed in a wide range of voltages, temperatures, and time under bias. Gas generation and the level of internal pressure have been calculated in Part II for different case sizes and different hermeticity leak rates to assess maximal allowable leakage currents. Effects related to electrolyte penetration to the glass seal area have been studied and the possibility of failures analyzed in Part III. Recommendations for screening and qualification to reduce risks of failures have been suggested

INVESTIGATING PRE-BREAKDOWN CURRENTS IN POLYMER TANTALUM CAPACITORS

Poly(3,4-ethylenedioxythiophene) (PEDOT), a conducting polymer, has been used since the 1990s for the cathode of tantalum capacitors, which have a tantalum anode, and a layer of tantalum pentoxide as the dielectric. Such capacitors are referred to as Polymer Ta capacitors. The first method, an in situ polymerization technique, used to deposit the polymer resulted in capacitors with a significant leakage current and breakdown voltages near 50 V. The second method, a pre-polymerization (pre-poly) technique, resulted in capacitors that have a much lower leakage current and a higher breakdown voltage than the in situ capacitors. In this thesis, an accurate measurement technique for dielectric leakage current, also referred to as the pre-breakdown current, was established for capacitors. Current versus time measurements at constant voltage were performed at several voltages and the results were compiled to obtain the current-voltage (I-V) characteristics of both in situ and pre-poly types of capacitors. These characteristics were then modeled and analyzed, which led to the conclusion that the pre-breakdown current is controlled by the Poole-Frenkel mechanism in the in situ capacitors and by both the Poole-Frenkel and Schottky mechanisms in the pre-poly capacitors. Current versus time measurements were also performed at various temperatures to obtain the activation energy for the current in the capacitors and to verify the leakage mechanisms. Results suggest the presence of shallow 0.15 eV traps in the dielectric of the in situ capacitor and deeper 0.75 eV traps in that of the pre-poly capacitor. Additionally, pre-poly capacitors also have a 0.54 eV Schottky barrier that limits the electrons from being emitted into the dielectric from the electrode. Both the deep trap levels and the Schottky barrier explain the lower leakage current and higher breakdown voltage observed in the pre-poly capacitors as compared to the in situ capacitors

Physical and Electrical Characterization of Aluminum Polymer Capacitors

Conductive polymer aluminum capacitor (PA capacitor) is an evolution of traditional wet electrolyte aluminum capacitors by replacing liquid electrolyte with a solid, highly conductive polymer. On the other hand, the cathode construction in polymer aluminum capacitors with coating of carbon and silver epoxy for terminal connection is more like a combination of the technique that solid tantalum capacitor utilizes. This evolution and combination result in the development of several competing capacitor construction technologies in manufacturing polymer aluminum capacitors. The driving force of this research on characterization of polymer aluminum capacitors is the rapid progress in IC technology. With the microprocessor speeds exceeding a gigahertz and CPU current demands of 80 amps and more, the demand for capacitors with higher peak current and faster repetition rates bring conducting polymer capacitors to the center o( focus. This is because this type of capacitors has been known for its ultra-low ESR and high capacitance. Polymer aluminum capacitors from several manufacturers with various combinations of capacitance, rated voltage, and ESR values were obtained and tested. The construction analysis of the capacitors revealed three different constructions: conventional rolled foil, the multilayer stacking V-shape, and a dual-layer sandwich structure. The capacitor structure and its impact on the electrical characteristics has been revealed and evaluated. A destructive test with massive current over stress to fail the polymer aluminum capacitors reveals that all polymer aluminum capacitors failed in a benign mode without ignition, combustion, or any other catastrophic failures. The extraordinary low ESR (as low as 3 mOMEGA), superior frequency independence reported for polymer aluminum capacitors have been confirmed. For the applications of polymer aluminum capacitors in space programs, a thermal vacuum cycle test was performed. The results, as expected, show no impact on the electrical characteristics of the capacitors. The breakdown voltage of polymer capacitors has been evaluated using a steady step surge test. Initial results show the uniform distribution in the breakdown voltage for polymer aluminum capacitors. Polymer aluminum capacitors with a combination of very high capacitance, extraordinary low ESR, excellent frequency stability, and non-ignite benign failure mode make it a niche fit in space applications for both today and future. Polymer capacitors are apparently also the best substitutes of the currently used MnO2-based tantalum capacitors in the low voltage range. However, some critical aspects are still to be addressed in the next phase of the investigation for PA capacitors. These include the long term reliability test of 125 C dry life and 85 C/85%RH humidity, the failure mechanism and de-rating, the radiation tolerance, and the high temperature performance. All of the above requires the continuous NEPP funding and support

Capacitor Technologies, Applications and Reliability

Various aspects of capacitor technologies and applications are discussed. Major emphasis is placed on: the causes of failures; accelerated testing; screening tests; destructive physical analysis; applications techniques; and improvements in capacitor capabilities

Reliability studies on solid tantalum electrolytic capacitors by means of accelerated life tests

The purpose of this thesis is to understand the failure mechanisms in Solid Tantalum Capacitors encapsulated in plastic, and to suggest the precautionary measures that prevent the occurrence of these failures. The reliability of Solid Tantalum Capacitors encapsulated in plastic is of considerable interest because in some applications where the mechanical accelerations or shocks are considerable the better hermitically sealed type are not able to sustain themselves. Poor adherence between the dielectric film and the base metal Tantalum under the conditions of sudden mechanical shocks, causes problems. Our study was carried out in two different directions, theoretical and experimental. The theoretical part is comprehensive review of the work done on Tantalum Capacitors from 1960 to upto date. The experimental part of the study is done by means of accelerated life testing under the conditions of high humidity & high temperature as well as various high temperatures without added humidity

Characterization of Polymer Hermetic Sealed Tantalum Capacitors Using Thin-film Devices

Polymer Hermetic Sealed (PHS) capacitors are advanced polymer capacitors with a hermetic seal enclosing the materials inside a metal enclosure. Their primary features include leakage current stability, high volumetric efficiency, and low weight compared to both wet and solid-state polymer tantalum capacitors. However, Life Tests performed on these capacitors have revealed a failure to withstand their rated voltage in a working temperature range over the long-term. There are also other interesting properties which have been observed such as Breakdown voltage (BDV) exceeding the Formation Voltage (Vf), anomalous transient currents, and a larger than expected capacitance dependence on temperature, C(T). A primary goal in this research is to understand whether the observed characteristics of PHS capacitors are a result of their complex structure or due more to the nature of interactions between the organic and inorganic material layers present. C(T) and BDV measurements were performed on thin-film MIS capacitors representing the material layers of PHS capacitors. Measurements were performed in the voltage range (0V-100V), a temperature range (-550C to 1250C), with varying frequency (20-10kHz), under both humid and dry conditions. Furthermore, one sample went through a curing process referred to as Heat Treatment , which is thought to improve device stability. Results from these measurements show that thin-film devices can be reasonable representatives of discrete PHS capacitors, and the properties observed in PHS capacitors are significantly dependent on the material layers in the capacitors. Thus, the thin-film MIS capacitor is shown to be a useful test structures for investigating physical phenomena observed in the more complex polymer Ta capacitor structure