Gas Phase Anodization of Tantalum


The anodic oxidation of tantalum in the gas phase was studied using an electromagnetic, ion cathode. The anodic films were prepared at constant current densities of 1.0 and 2.0 ma/cm 2. The growth characteristics of anodic tantalum oxide films, in the gas phase, were found to be similar to films prepared in liquid electrolytes. A comparison is made between the results Of this study and other reported gas phase reactions with various anode surfaces. The tantalum oxide growth, for the experimental conditions reported here, is shown to be l inearly dependent on the total charge passed in the anode circuit during the reaction up to a formation voltage of 200v. Tantalum oxide films prepared by anodic reactions in aqueous and nonaqueous electrolytes have been shown to contain impurities from the solution (1-3). Anodic oxide films prepared in an oxygen discharge (4-7) have been found to exhibit physical and elec-trical properties analogous to those found with films formed in l iquid electrolytes. Certain aspects of the growth of films by anodization in liquid electrolytes are similar to those observed during gas phase anodi-zation. Examples are the relationship between thick-ness and the formation voltage and the current decay at constant voltage. Some authors (5) report the presence of a large electron population in the gaseous electrolyte and anode temperatures as high as 200 ~ during anodiza-tion. This paper reports the use of an electromagnetic ion cathode which was designed to limit the electron and positive ion concentration in the gaseous elec-trolyte. Separation of the ion cathode from the anode reduces heating effects of the anode and allows for the observation of the anode reaction without the mask-ing effects of a general discharge. Results are com-pared with anodic oxidation of tantalum in aqueous electrolytes and with gas phase anodization f var i-ous materials as reported by others

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