Tantalum Capacitor

Tantalum capacitor

The tantalum capacitor is a high reliability form of electrolytic capacitor in which the dielectric is formed from a very thin anodized layer of tantalum pentoxide.

• 1 Types and Construction
• 2 Advantages and disadvantages
• 3 Uses
• 4 References

In military grade tantalum capacitors, the anode consists of a small cylindrical billet of tantalum metal held inside a sterling silver can, which forms the cathode, by teflon spacers. A tantalum lead exits the can via a teflon and silicone rubber gasket at one end. This tantalum lead is spot welded to a copper lead outside the can. An electrically conductive jelly fills the space between the inside wall of the silver can and the surface of the tantalum billet, which is covered by the steel blue layer of oxide which is the dielectric barrier.

A cheaper form consists of a similar sintered tantalum billet, coated in manganese IV oxide and an electro-deposited layer of silver, this being soldered inside a tin plated brass can with an enameled glass seal at one end.

The cheapest form consists of a mixture of tantalum powder and manganese IV oxide pressed into a solid chalky mass around a tantalum wire, this is coated with silver and dipped into coloured epoxy resin resulting in a small coloured bead with two leads.

Tantalum capacitors possess very low electrical leakage, (high leakage resistance), and will retain a charge for a long duration, they are also more tolerant of harsh, hot operating environments unlike standard aluminium electrolytic capacitors. Tantalum capacitors are relatively expensive, particularly the military grades, they are not particularly tolerant of heavy charge and discharge currents, particularly of a repetitive nature and their effective series resistance, ESR, is quite high when compared to aluminium electrolytics. As with all electrolytic capacitors, correct polarity must be observed otherwise the capacitor will depolarize and the dielectric oxide layer will be reduced back to the metal, reducing the resistance of the device and causing it to become very hot and possibly explode. Tantalum capacitors are less prone to "drying out", causing a decrease in capacitance as is often the case with aluminium electrolytic capacitors particularly when used in hot environments. They maintain their designed capacitance under such conditions over long periods of time, (decades).

The low leakage and high capacity of tantalum capacitors favors their use in sample and hold circuits, (long hold duration), and some long duration timing circuits where precise timing is not critical. They are also often used for power supply rail decoupling in parallel with film or ceramic capacitors with low ESR and reactance at high frequency. Sometimes tantalum capacitors can replace aluminium electrolytic capacitors in situations where external environment or dense component packing results in sustained hot internal environment and high reliability is important.

Due to their higher cost, tantalum capacitors were rarely ever seen in consumer electronics, although the cheapest epoxy dipped types were sometimes used. Requirements for high quality and reliability, such as in medical electronics sees the use of many tantalum capacitors in this type of equipment.

Low-voltage tantalum capacitors are nowadays commonly used in large numbers for power supply filtering on computer motherboards and in peripherals due to their small size and long-term reliability.^[1][2]