Regensburg 2010 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 7: Dielectric and ferroelectric thin films

DF 7.1: Talk

Tuesday, March 23, 2010, 14:00–14:20, H11

Electrode polarization from a different point of view — •Björn Martin and Herbert Kliem — Saarland University, Germany

To investigate electrode and space charge effects thin film capacitance structures using ion-conducting polyethylene oxide contacted with metal electrodes are prepared.

In contrast to continuum models a discrete three-dimensional model is developed to describe the ionic motion. Single charges are regarded. Negative ions can fluctuate thermally activated over energy barriers in a multiwell potential. Positive immobile ions provide charge neutrality. Interactions of the ions with the electrodes using the method of images and all other electrostatic interactions are considered.

In simulations a coulombic attraction between the mobile ions and their image charges in the electrodes is found even in short circuit condition. The accumulated ions trapped at the electrodes together with their image charges yield dipole like fields repelling further ions towards the volume of the samples leaving behind a positive depletion zone. Thus, a maximum of the internal potential results in the middle of the sample which is verified experimentally.

With applied voltage the ions are partly detrapped. The mobile ions are shifted to the positive electrode and a broad depletion zone with positive immobile charges arises at the negative electrode. Therefore, a high potential drop is found here. In the bulk the potential increases only slightly indicating no space charges in this region.