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Advantages of tantalum capacitor

29 Jul 2015  | Charles Pothier

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Tantalum capacitors offer designers of densely packed, high-performance electronic circuits a reliable high-capacitance solution with stable performance. A historical favourite among design engineers, tantalum capacitors are found in a wide range of applications such as bulk energy storage, filtering, and decoupling. Advancements in tantalum capacitor technology include the maturation of the polymer cathode system, which brings lower effective series resistance (ESR), significant improvements in packaging density, and reductions in effective series inductance (ESL). Herein, we will examine the impacts these developments have had on performance.


Background
Tantalum capacitors have been in use for almost 60 years. Noted for their long-term reliability and capacitance density, tantalum capacitors have been central in the design of military and commercial avionics, implantable medical electronics, notebook computers, smartphones, and industrial automation and control systems.

At the core of their popularity has been their volumetric efficiency, which yields high capacitance per unit volume. Refer to the equation for capacitance:

C = (kA)/d


Where:

C = capacitance

k = dielectric constant

A = surface area

d = thickness of the dielectric


With an extremely large surface area, high dielectric constant, and a relatively thin dielectric, tantalum capacitors offer the best capacitance density available in the 1µF to 2,200µF range at working voltages up to 50V.

Combining advanced tantalum powders and high-efficiency packaging has kept tantalum capacitors one step ahead of advancements in alternate technologies. For example, today's tantalum capacitors are able to offer up to 22µF at 4V in the 0402 case size. At the other end of the voltage range, one can find tantalum capacitors of up to 47µF at 50V in a single package, and even higher in through-hole packaging.

Conventional tantalum capacitors utilise manganese dioxide (MnO2) as the cathode system. This semiconductor material provides a self-healing mechanism that leads to long-term reliability and is relatively inexpensive. However, its oxygen-rich formulation can contribute to ignition under extreme circumstances involving high heat. Since the mid-1990s, the industry has been working to mature conductive polymers, complementing the MnO2 offering. With significantly higher conductivity than MnO2, conductive polymers have contributed to the reduction of ESR. This advancement, coupled with the elimination of the ignition risk in sensitive applications, has helped drive investment in this technology.


Advancements in tantalum capacitor design
Manufactures offer solid tantalum capacitors in a wide variety of different series optimised for specific characteristics and targeting different applications and market segments. These varied product series include optimisations such as lower ESR, reduced size, high reliability (e.g., military, automotive, and medical), reduced DC current leakage, lower ESL, and higher temperature. This paper focuses on two of these areas of attention: lower ESR and reduced size.

Lower ESR: Optimised for lowest ESR, these devices offer higher efficiency in pulsed or AC applications and better filtering in high-noise environments.

Reduced size: Combining the use of high-CV tantalum powder and highly efficient packaging, these devices offer high capacitance in compact sizes. These are used in space-constrained applications such as smartphones, tablets, and other hand-held consumer electronics.

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