Progress in the Key Technologies for the Fabrication of High Specific Capacitance of Aluminum Electrolytic Capacitors

The worldwide market for aluminum electrolytic capacitors (Al E-caps) was about USD 4.805 billion in 2004, among which the production in China took approximately 40%. Besides, the Al E-cap market in China continues to grow by over 15% per year due to the increased demands from IC and ISI devices. This paper carries out a brief survey on the key technologies for the fabrication of high specific capacitance of Al E-caps. The recent development in both composite alumina films with high dielectric constant and working electrolytes for Al E-caps is discussed in detail, jncluding related technological difficulties and problems. Three different methods to manufacture alumina composite films with high dielectric constants, the sol-gel coating, hydrolysis precipitation and electrophoretic precipitation, are reviewed. Commonly-used solvents, solutes and additives in the working electrolyte for Al E-caps and their performances are analyzed in this paper. Solid electrolytes, including organic semiconductive electrolytes 7,7,8,8-tetracyanoquinodimethan (TCNQ) and its complex salts, and conducting polymers, such as polypyrrole, polyaniline and poly(3,4-ethylenedioxytiophene) are compared. Some ionic liquids, a new type of electrolyte applied for V-chip Al E-caps, are also discussed. The future trends on high specific capacitance of Al E-cap are proposed.