Conductive Polymer Usage in Capacitors:

Conductive polymer usage in electrolytic capacitors on a mass scale has been well documented since the introduction of the NEOCapacitor by NEC Tantalum Corporation in 1995 (now Tokin Corporation), which was in response to the developmental work of Sony Video Components in Japan. In fact, in a 1995 interview of IBM Paumanok learned that Sanyo was their preferred supplier for decoupling the Pentium Processor. They noted that Sanyo was instrumental in the development of the OSCON capacitor.

This capacitor was based upon a radial leaded aluminum electrolytic capacitor design that used a complex salt structure known as isoquinolinium to develop a high voltage, high capacitance design with very low ESR. Sanyo and NEC were also quick to note the potential to displace the manganese nitrate used for coating tantalum anodes with conductive polymer. Pyrole was chosen and this polymer was polymerized and pressurized as a “skin” into the nodules that make up the surface area of a tantalum anode. ESR dropped dramatically by the use of polypyrole in solid electrolytic chip capacitors, which proved critical in decoupling high frequency microprocessors in multiple applications that Kemet soon licensed the NEOCapacitor as the KO Capacitor for distribution in the west. Kemet also began their own study of electro conductive polymers.

Meanwhile, back in Japan, Matsushita Electric Industrial Circuit Capacitor Division (now Panasonic Electronic Devices) developed the D Case polymer aluminum SP-Cap, which offered excellent ESR in a molded chip package with the use of a crimped aluminum anode covered in a skin of organic polypyrole as the cathode. This cathode skin replaced the traditional aluminum foil cathode in a package that was similar in size and shape to the best selling tantalum capacitors. Between 1995 and 2005 multiple vendors introduced capacitors with conductive polymer as the cathode. The large volumes consumed are in the molded and coated tantalum chip capacitors, horizontal aluminum chip capacitors, vertical chip aluminum capacitors and radial leaded aluminum capacitors. Experimentation is underway for the use of conductive polymers in electric double layer carbon capacitors in Korea and Japan today. Additionally, development is underway for the use of polymer cathode in niobium capacitors (NEC says they have a niobium with polymer, and AVX says they are working on one).

Why Lower the ESR?

ESR is an industry buzzword. It means equivalent series resistance, and the lower the ESR the better. Lowering the ESR increases the speed at which the capacitor can release its charge. This speed is important for decoupling microprocessors. Single digit ESR is the near term target, and ESR ratings less than 1 are envisioned by the customer.

Conductive Polymers in Use:

There are three conductive polymers currently in use as cathode materials in the capacitor industry. These include polypyrole, polythiophene and polyaniline and multiple derivations thereof. Two additional conductive polymers exist although Paumanok notes no known usage of these additional conductive polymers outside of the electroluminescent display markets. Polypyrole is the polymer that has the largest usage across both tantalum and aluminum capacitor markets and is the most heavily consumed worldwide. Polythiophene, however, is becoming a larger part of the growing market, while polyanailine is being used in addition to the other polymers for unique purposes that enhance the performance of the finished anode.

Difference in Conductive Polymer Performance in the Finished Capacitor:

Paumanok has determined that while each of the conductive polymers have different prices (with polypyrole being the least expensive and polanaline being the most expensive) there is no difference in performance of any of the polymers. All three offer very similar ESR performance in the finished capacitor. However, capacitor vendors have varying ESR ratings that are disproportional to the limited number of conductive polymers to choose from, which means that other aspects of the production process are key to lowering the ESR.

What Really Lowers the ESR:

In a capacitor anode that employs a conductive polymer cathode, the key to lowering the ESR to its lowest levels, in addition to replacing manganese nitrate or aluminum cathode materials with conductive polymer, is to increase the surface area of the capacitor anode. This applies to both tantalum and aluminum capacitor technologies respectively, and explains why multianode designs and large single anodes offer the lowest ESR. Even with MN02 tantalum capacitors this phenomenon exists, so it is obvious that in larger case sizes or in multianodes with conductive polymer, ESR can be lowered to the single digit level. This is why most of the competition between the solid polymer electrolytic capacitors is in the D case size. In fact, solid polymer aluminum capacitors are only available in D case sizes and variations of that size. Conductive polymer is also popular in larger case sizes in tantalum, but sales are excellent for portable digital electronics and in audio circuits where volumetric efficiency, low ESR, high capacitance and low piezoelectric effect can be satisfied only by polymer tantalum.

Production Processing Differentiation:

Since the number of available polymers for use in capacitors is limited and the number of vendors selling these parts is large, with ESR capabilities varying by so very much among these manufacturers the logical conclusion is that processing differentiation among the vendors is also key. For example, the best ESR will be found in the capacitor that has the most consistent coverage of the polymer among the nodules of the tantalum anode. This has been attempted by a gas diffusion process and a traditional cathode dipping process. ESR can further be improved by the type of capacitor grade tantalum metal powder used. Higher CV/g (Capacitance Value Per Gram) are not as good as lower CV/g tantalum metal powders in lowering ESR. Some vendors have discovered this and now employ the same in their selection of powders used in anodes for their polymer line.

Market Leaders:

Based upon detailed competitive analysis of low ESR vendors of capacitors, Paumanok notes that in molded chips that Sanyo, Tokin, Kemet, EPCOS (now owned by Kemet) and Panasonic currently lead the field in terms of low ESR products and diverse product portfolios that offer the most voltage ratings, case sizes, and capacitance values.

Market Potential and Growth:

The low ESR market continues to be one of the fastest growth portions of the global capacitor industry as design engineers give increasing importance to ESR in addition to voltage, capacitance, operating temperature and price when buying electrolytic capacitors, although price continues to be the most important criteria of negotiation regardless of how fast the capacitor releases its charge. As for the vendors of conductive polymers selling to capacitor vendors, these plastics producers will continue to grow at a rate in accordance with the market and have the entire manganese nitrate market to take over.