Solid Electrolyte Capacitors

Clevios™ Conductive polymers are essential for low ESR (Equivalent Series Resistance) electrolytic capacitors. Because of its high conductivity and outstanding temperature stability the conductive polymer poly (3,4-ethylenedioxythiophene), also known as PEDOT, is widely used in the capacitor industry to manufacture polymer type tantalum, niobium and aluminium capacitors.

Classical capacitors are made using a metal anode, typically an aluminium foil or a sintered compact of tantalum or niobium powders. Since the capacitance is directly related to the electrode’s surface area, the aluminium foil is roughened by an etching process. tantalum or niobium powders have inherently large surface areas. The dielectric layer is formed by an anodic oxidation process and consists of the respective metal oxides. To complete the capacitor structure , a counter electrode is applied on top of the metal oxide layer. Conventional tantalum capacitors use manganese dioxide contacted via additional graphite and silver layers . The counter electrode of an aluminium winding type capacitor has a second aluminium foil that is part of the wound capacitor element, consisting of an aluminium anode and cathode foil with a separator soaked and filled with a liquid electrolyte.

In modern capacitors Clevios™ materials have replaced the manganese dioxide and the liquid electrolyte resulting in more stable and efficient elements used in the electronics applications such as mobile phones and note books and is now an industry standard.

Aluminum Capacitors:
• Etched aluminum anode foil
• Electrochemical generation of Al2O3 as dielectric
• Separator
• Aluminum cathode foil
• Poly[3,4-ethylenedioxythiophene], (PEDOT)

Tantalum Capacitors:
• Sintered tantalum powder
• Electrochemical generation of Ta2O5 as dielectric
• Poly[3,4-ethylenedioxythiophene], (PEDOT)

Many process steps are necessary to apply the manganese dioxide as the counter electrode during capacitor manufacture. Also, the conductivity of the manganese dioxide and electrolytes are too low to achieve excellent high frequency properties required on the capacitor. There were many attempts to replace Mn O2 and electrolytes with conductive polymers which are not only more conductive but also can be easier to apply.

By using PEDOT, via the in-situ polymerization of Clevios™ M and Clevios C, as the cathode material these hurdles are now overcome. PEDOT outperforms any other technology due to its outstanding heat stability and superior conductivity. For the chemical in-situ polymerization process to prepare PEDOT, Heraeus offers a wide range of Clevios™ C grades, solutions of iron salt oxidizers, and Clevios™ M the EDOT monomer.

The Clevios™ K product line-up is the newest generation of Heraeus proprietary conductive polymer products and a milestone for the production of solid electrolyte capacitors.

Clevios™ K can greatly simplify the impregnation process during production, because it contains the already polymerized conductive polymer; it is ready-to-use. Application is very fast and easy; only dipping and drying is required which ensures good process control and high material yield.

In terms of capacitor performance, Clevios™ K shows various advantages compared to the in-situ chemical polymerization (Clevios™ M and Clevios™ C). Clevios™ K is the key to extend the voltage range of tantalum- and aluminum-polymer capacitors to considerably higher working voltages. It shows an improved thermal stability compared to in-situ chemical PEDOT. Furthermore, Clevios™ K products are waterborne and do not contain hazardous solvents, therefore, handling and storage are safer, following the trends of ever increasing environmental specifications.