Reliability comparison of tantalum and niobium solid electrolytic capacitors

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This paper deals with a comparative investigation of tantalum and niobium solid electrolytic capacitors. Nb is an attractive replacement for Ta in solid electrolytic capacitors because it is lighter and cheaper than Ta. Although these two metals have much in common in their crystalline structure and physical and chemical properties, the electrical properties of Ta and Nb capacitors are different. Particularly, most Nb capacitors are characterized by an increase in direct current leakage during life testing. This causes parametric failure of Nb capacitors. On the other hand, the direct current leakage of Ta capacitors does not change significantly for a long time, but then increases sharply for some samples. Hence occasional catastrophic failures are typical for Ta capacitors. Nevertheless, the properties of high-CV Ta capacitors with low and high rated voltage approach the properties of Nb capacitors. The physical nature of these phenomena is discussed. © 1998 John Wiley & Sons, Ltd.