Aluminum electrolytic capacitors are used in various applications because they can achieve high capacitance and voltage ratings in small, cost efficient case sizes. In order to understand how this is accomplished, we must examine some of the basic properties of capacitors.
A capacitor is made up of two parallel plates, the electrodes, with a dielectric between them. The amount of capacitance is directly proportional to the surface area of the electrode. If we double the surface area of the electrode, we double the capacitance. The amount of available capacitance is also inversely proportional to the dielectric thickness. If we reduce the thickness by one-half, the capacitance is doubled.
The high volumetric efficiency of an electrolytic capacitor is due to its enhanced plate surface area and a very thin dielectric layer. A very large internal surface can be created on the aluminum electrodes by electrochemical etching. The dielectric is an oxide and has a high dielectric strength which is electrochemically deposited in very thin layers. This combination produces a high capacitance in a small volume.
Since 1965, the case size of aluminum electrolytic capacitors has been reduced to realize a volumetric reduction of almost five times.
Miniaturization has been achieved by the development of new etching technology, improvements in the oxide layer and advancements in production engineering. All this has been accomplished without the significant increase of ESR (equivalent series resistance) or degradation of frequency and temperature characteristics. An example of the technical advancements in electrolytes and oxide formation is the extended operating temperature range from -25 ~ +70°C to -55 ~ +130°C.