Effect of Light Elements (N, C, O) in Tantalum on Tantalum Film Capacitor Properties

The results of this study demonstrate that addition of either carbon or nitrogen to tantalum is desirable not only for meeting the 50 volt dc leakage current criterion used on 230 V tantalum film capacitors, but also for optimizing capacitor reliability. Since both dopants lower the capacitance density by about 1% and 0.35% for each atomic (at',, % of N or C, respectively, the amounts added to tantalum should be kept as low as possible. Two at % of nitrogen or three at % carbon are sufficient to realize their beneficial, effect on capacitor leakage current and capacitor reliability, while addition of oxygen (up to 20 at %) does not improve capacitor quality. Possible effects of nitrogen and carbon doping on the electronic structure (band structure) of the anodic oxide will be discussed.