Dielectric Films in Aluminum and Tantalum Electrolytic and Solid Tantalum Capacitors

The characteristics of electrolytic capacitors are determined primarily by the nature of the dielectric oxide film. The nature of this film and the factors which influence its physical and chemical characteristics are discussed. Electron photomicrographs of the electrolytic oxide film on aluminum, as well as X-ray diffraction and direct electrical measurements of the dry oxide film, reveal that it is crystalline \gamma-A1
2
O
a
. The characteristics of electrolytic Ta
2
0
5
films on tantalum are compared with those on aluminum, and the factors that make tantalum capacitors more reliable are indicated.