Charge Storage Effects in Tantalum Oxide Films

Abstract

The phenomenon of the residual discharge current following an inverse time law, inormalres∝b/t , was confirmed for tantalum electrolytic capacitors. It was shown that the coefficient b was independent of charging fields up to 2/3 of the formation field and that the residual current increased with temperature. The activation energy was 2.5 kcal/mole. Furthermore, it was shown that, if the external resistor was removed and the cell was left with open terminals, the internal residual current continued to flow until the build‐up field modified the flow. If the oxide film were illuminated during discharging, two different photoeffects were recorded: the transient effects due to wavelengths of 320 mµ to about 600 µ and the stationary photocurrent mostly due to wavelengths shorter than 300 mµ.Several models are discussed which lead to an inverse time law. Preference was given to the idea that a net positive space charge arises within the oxide during charging; that this space charge causes two internal fields of opposite directions and that the residual discharge current is the difference of two currents flowing in the opposing fields, thus neutralizing the space charge. Irradiation during charging and discharging affected the positive transient effect and the space charge field.

Correlation between Electrical and Optical Properties of Tantalum Anodic Oxide and Electron Cyclotron Resonance Etching Studies of E-Beam Deposited Ta2O5Films

“…Figure 1 shows I versus t and Figures 2a and 2b show optical the ellipsometric data n versus λ and α versus λ, respectively, for samples A and B. The current decay for anodic tantalum oxide samples always follows the power function with the power value of "∼−1" when the anodization is good 9 as seen for sample A (Eq. 1).…”

On the Mechanisms of Electrolytic Rectification

“…Lindmayer (54) considered discharge transients from a dielectric sandwiched between metal electrodes. He also observed an inverse time relationship, as did Dreiner (84). In view of what has just been said it is clear that double injection is also a definite possibility if protons can be injected into an oxide film.…”

“…The threshold for photoconductivity in Nb/Nb2OJAu diodes is about 1.2 ev and is attributed to excitation of electrons from an impurity band. The effect of illumination on stored charge from Ta/Ta2Oh/ electrolyte was studied by Dreiner (84). To explain the inverse time law for the residual discharge current, a model is proposed in which a positive space charge in the film, generated during the forming process, gives rise to two opposing electric fields in the oxide.…”

Solid-State Anodic Oxidation of Tantalum

“…If the amount of dielectric healing is sufficiently extensive, the characteristic battery-like behavior of these areas may become apparent. This effect, coupled with residual voltages of the type described by Dreiner (14), may account for some of the complicated opencircuit voltage behavior reported for Ta-Ta2Os-MnO2 capacitors by Law and Richards (15).…”