The engineer’s guide to niobium electrolytic capacitors

This article is part of The engineer’s complete guide to capacitors. If you’re unsure of what type of capacitor is best for your circuit, read How to choose the right capacitor for any application.

What is a niobium electrolytic capacitor?

Niobium electrolytic capacitors are one of a few types of electrolytic capacitors you should consider for your electronic circuit. Aluminum electrolytic capacitors offer great volumetric efficiency (capacitance compared to size), are relatively inexpensive and are readily available. Tantalum electrolytic capacitors offer some improvements over aluminum electrolytic capacitors, but are more expensive and can have longer lead times. When tantalum capacitors are not available, niobium capacitors are the next choice.

Niobium is a sister metal to tantalum and shares many chemical characteristics. Niobium electrolytic capacitors offer a few disadvantages and several advantages when compared to tantalum electrolytic capacitors.

Niobium capacitor technology appeared on the market in 2002 when Vishay offered early sampling and announced preproduction. When compared to tantalum, niobium is limited in its maximum rated voltage, lower volumetric efficiency, incompatibility with low equivalent series resistance (ESR) polymer electrodes and a limited range of values. Several vendors keep this technology as a niche line of the tantalum capacitor industry today. But some advantages of niobium electrolytic capacitors—including safety, reliability and lower cost—are worth closer examination and consideration.

Comparison of niobium and tantalum electrolytic capacitors

Tantalum capacitors are often used in power supply filter circuits where a large bulk capacitance is needed. Power supply filter applications can result in increases in peak voltage or current. A current surge, a large ripple current or an overvoltage spike can cause a tantalum capacitor to fail. When its dielectric breaks down, the heat generated by a large current flowing through a defect site will produce dielectric destruction. There will be a chemical reaction that can produce flaming.

The niobium capacitor design is very different. During a dielectric breakdown event, the temperature rise is significantly lower than for tantalum. The niobium oxide layer tends to grow at elevated temperatures resulting in a “self-arresting” feature. As a result, niobium capacitors reduce the ignition failure mode by 95% compared to tantalum capacitors. For this reason, niobium oxide capacitors are regarded to be one of the safest available capacitor technologies.

The below table compares several characteristics of niobium and tantalum oxide layers.

Applications of niobium electrolytic capacitors

Niobium electrolytic capacitors are regarded as substitutes for tantalum electrolytic capacitors, and their applications are similar. However, in low voltage (3.3 V or 5 V) applications, niobium capacitors are preferred because of their “non-burn” failure mode. In contrast, tantalum capacitors can become short circuits when they fail, which can produce arcs or flames.