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Dielectric properties of thin insulating films Wilcox , Philip Stanley

Abstract

The dielectric polarization processes, conduction mechanisms and space charge effects occurring in tantalum / tantalum pentoxide / metal devices are investigated. The dielectric properties are analyzed on the basis of an ionic relaxation process with a nearly flat distribution of activation energies. This distribution leads to step response polarization currents following an inverse time law. The effect of an injected electronic space charge on the response of the device due to the removal of a step voltage is analyzed and results are given demonstrating this effect. The devices used exhibit a rectification behaviour. For tantalum positive the currents follow a Schottky law and for tantalum negative, the bulk Poole-Frenkel law. Hysteresis effects are observed as well as the effects of a space charge on the Schottky law currents. On one sample, sufficiently high fields causes an increase in the conductance by a factor of 10³ to 10⁵. For this deformed sample, no hysteresis or rectification is observed and the currents follow a Schottky law for both polarities. The validity of the ionic relaxation model is discussed in light of the observed dielectric losses at low temperatures. The experimental results indicate that an electronic rather than an ionic process could be responsible for the dielectric losses.

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