If you take a look at the main board of an electronic device such as a personal computer, you’re likely to see some of the six types of capacitors shown below (Fig. 1).
Common types of capacitors include tantalum electrolytic capacitors (MnO2 type and polymer type), aluminum electrolytic capacitors (electrolyte can type, polymer can type, and chip type), and MLCC.
There are many other types of capacitors, such as film capacitors and niobium capacitors, but here we will describe polymer capacitors, a type of capacitor produced by Murata among others.
In both tantalum electrolytic capacitors and aluminum electrolytic capacitors, a polymer capacitor is a type of electrolytic capacitor in which a conductive polymer is used as the cathode.
In a polymer-type aluminum electrolytic capacitor, the anode is made of aluminum foil and the cathode is made of a conductive polymer.
In a polymer-type tantalum electrolytic capacitor, the anode is made of the metal tantalum and the cathode is made of a conductive polymer.
Figure 2 shows an example of this structure.
In conventional electrolytic capacitors, an electrolyte (electrolytic solution) or manganese dioxide (MnO2) was used as the cathode. Using a conductive polymer instead provides many advantages, making it possible to achieve a lower equivalent series resistance (ESR), more stable thermal characteristics, improved safety, and longer service life.
As can be seen in Fig. 1, polymer capacitors have lower ESR than conventional electrolytic capacitors.
Note that the type of valve metal used for the anode basically determines the type of dielectric, and this in turn determines the dielectric constant and DC bias characteristics, as well as the acoustic noise characteristics.
Thus, a wide variety of characteristics can be obtained by combining anodes, cathodes, and dielectrics made of different materials. Each has its own strong and weak points, and these must be kept in mind when selecting components as part of the circuit design process.