The effect of moisture and metallic contact area has been investigated on the asymmetry properties of anodic tantalum oxide films, approximately 2400Aå thick. Moisture has been reversibly desorbed and adsorbed by vacuum baking followed by exposure at 50–85% RH. The cathodic currents are not affected significantly by this cycle, while the anodic leakage and charging current can be changed by factors of 106 and 102, respectively. The contact area experiment confirm previous results that the asymmetry is due to local inhomogeneities in the oxide film, since nonpolar characteristics, in the absence or presence of moisture, can be obtained with a contact area less than 0.01 mm2. This result indicates that the moisture effect is associated with defects in the oxide film. The oxide film can thus be considered as a normal dielectric with high symmetrical anodic and cathodic breakdown voltages. Distributed on the average 0.1 mm apart throughout the film are heterogeneities of an unknown nature which cause a symmetrical but lower breakdown than the rest of the oxide. The asymmetry results from an increase in the anodic breakdown at these distinct sites due to the presence of water.
Reactively sputtered films consisting of ∼65 atom per cent (a/o) Ta and ∼35 a/o Si are of considerable interest for forming thin film capacitors and resistors. Oxides have been anodically grown on Ta‐Si films and examined by the Rutherford backscattering technique. This analysis revealed that the outer layer of the oxide is greatly enriched in Ta and almost devoid of Si, while the inner layer has a lower Ta:Si ratio than the as‐sputtered film. This indicates that Ta cations are very mobile within the oxide and are migrating to the surface under the influence of the applied field during anodization. No appreciable dissolution of either Ta or Si takes place. The Ta:Si:O stoichiometry of the oxide is consistent with a film composed of Ta2O5 and
SiO2
.
The suitability of niobium as the anode for solid electrolytic capacitors has been investigated. Field crystallization of the amorphous niobium oxide film has been found to be a determining factor for the properties of these capacitors. Purity of the porous anodes as dependent on the sintering conditions, formation temperature and voltage, and formation electrolytes, parameters all known to control the initiation of crystallization, have been correlated with the initial and life test properties of these capacitors. The initial properties of niobium solid electrolytic capacitors prepared under optimum conditions compare favorably with equivalent tantalum components. However, with the current purity of niobium powder, only units with operating voltages up to 20 v survive a life test at 85°C, with the failures of capacitors rated at higher voltages attributed to the partial crystallization of the amorphous film during formation.
Sputtered tantalum‐titanium alloy thin films have been anodized in 0.01% aqueous citric acid, and the atom distribution, stoichiometry, and thickness determined by Rutherford backscattering analysis and stylus measurement. The anodic oxide film consists of a uniform amorphous mixture of
Ta2O5
and
TiO2
with about 3% of the oxide at the electrolyte interface consisting of almost pure
TiO2
. During anodization a small fraction of the titanium dissolves in the electrolyte. The apparent growth constant of the anodic oxide on
Ta0.49Ti0.51
films is
1.88±0.02 normalnm/V
. The density of the oxide is determined as
false(5.9±0.2false)×103 normalkg/m3
. From aqueous contact capacitance measurements, the dielectric constant of the alloy anodic oxide is
24.7±0.9
.
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