Tantalum and Niobium oxide capacitors: Field crystallization, leakage current kinetics and reliability

The study of the charge carrier transport in Ta and NbO capacitors was performed to analyze the leakage current kinetics at high temperature and high electric field for MnO₂ and Conducting Polymer (CP) cathode. Leakage current of Ta and NbO capacitors at the room temperature is driven by the Ohmic and Poole-Frenkel mechanism at the rated voltage. It was found that these capacitors are very stable for temperature below 100°C. High temperature and high voltage applications are considered to be limited by the field crystallization mechanisms and ions diffusion. The leakage current changes in high electric field and at the elevated temperature T = 400 K could be divided into three time intervals: (i) Leakage current is stable (in some samples is slightly decreasing or increasing) during a period of 1 to 10 days. (ii) Leakage current increases with the slope 5 to100 pA/s for time interval about 10 days. (iii) Leakage current is stable or slightly increases with the slope less than 1 pA/s. Activation energy decreases during the ageing period from 0.55 to 0.45 eV. Leakage current variations are partly reversible. Irreversible changes of leakage current appear on about 1% of samples after ageing. Further investigation in this field can lead to the enhancement of reliability and performance of these capacitors.