Tantalum Printed Capacitors

Abstract

It has previously been considered either impossible or impractical to make tantalum oxide capacitors by applying a metal counter electrode directly to a tantalum oxide film. Attempts in this direction have led to either direct shorts or low breakdown strength. For this reason, it has been presumed that it was essential to use either an electrolyte or a semiconductor in the cathode structure. Using sputtered tantalum films as the base for the anodized oxide film, however, excellent results have been achieved employing evaporated metal counter electrodes. Many of the properties of units made in this way are superior to those of other types of tantalum capacitors. Capacitances obtained are comparable to the capacitance-area relationships for tantalum electrolytic capacitors formed to the same voltages. DC leakages, however, have been found to be much lower than values reported for those of tantalum electrolytic units. Another advantage is that these units are capable of withstanding higher voltages than will tantalum solid electrolytic capacitors formed to the same voltage. Indeed, voltages equal to the anodizing voltage may be maintained on the capacitor without impairment. Capacitors have also been produced with thin films of other anodizable metals, evaporated aluminum in particular. This type of capacitor should find many applications in the lower capacitance areas, and seems ideally suited for printed circuit applications.