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Varistor piezotronics: Mechanically tuned conductivity in varistors

Baraki, Raschid and Novak, Nikola and Hofstätter, Michael and Supancic, Peter and Rödel, Jürgen and Frömling, Till (2015):
Varistor piezotronics: Mechanically tuned conductivity in varistors.
In: Journal of Applied Physics, pp. 085703(1-9), 118, (8), ISSN 0021-8979, [Online-Edition: http://dx.doi.org/10.1063/1.4929360],
[Article]

Abstract

The piezoelectric effect of ZnO has been investigated recently with the goal to modify metal/semiconductor Schottky-barriers and p-n-junctions by application of mechanical stress. This research area called “piezotronics” is so far focused on nano structured ZnO wires. At the same time, ZnO varistor materials are already widely utilized and may benefit from a piezotronic approach. In this instance, the grain boundary potential barriers in the ceramic can be tuned by mechanical stress. Polycrystalline varistors exhibit huge changes of resistivity upon applied electrical and mechanical fields and therefore offer descriptive model systems to study the piezotronic effect. If the influence of temperature is contemplated, our current mechanistic understanding can be interrogated and corroborated. In this paper, we present a physical model based on parallel conducting pathways. This affords qualitative and semi-quantitative rationalization of temperature dependent electrical properties. The investigations demonstrate that narrow conductive pathways contribute to the overall current, which becomes increasingly conductive with application of mechanical stress due to lowering of the barrier height. Rising temperature increases the thermionic current through the rest of the material with higher average potential barriers, which are hardly affected by the piezoelectric effect. Hence, relative changes in resistance due to application of stress are higher at low temperature.

Item Type: Article
Erschienen: 2015
Creators: Baraki, Raschid and Novak, Nikola and Hofstätter, Michael and Supancic, Peter and Rödel, Jürgen and Frömling, Till
Title: Varistor piezotronics: Mechanically tuned conductivity in varistors
Language: English
Abstract:

The piezoelectric effect of ZnO has been investigated recently with the goal to modify metal/semiconductor Schottky-barriers and p-n-junctions by application of mechanical stress. This research area called “piezotronics” is so far focused on nano structured ZnO wires. At the same time, ZnO varistor materials are already widely utilized and may benefit from a piezotronic approach. In this instance, the grain boundary potential barriers in the ceramic can be tuned by mechanical stress. Polycrystalline varistors exhibit huge changes of resistivity upon applied electrical and mechanical fields and therefore offer descriptive model systems to study the piezotronic effect. If the influence of temperature is contemplated, our current mechanistic understanding can be interrogated and corroborated. In this paper, we present a physical model based on parallel conducting pathways. This affords qualitative and semi-quantitative rationalization of temperature dependent electrical properties. The investigations demonstrate that narrow conductive pathways contribute to the overall current, which becomes increasingly conductive with application of mechanical stress due to lowering of the barrier height. Rising temperature increases the thermionic current through the rest of the material with higher average potential barriers, which are hardly affected by the piezoelectric effect. Hence, relative changes in resistance due to application of stress are higher at low temperature.

Journal or Publication Title: Journal of Applied Physics
Volume: 118
Number: 8
Uncontrolled Keywords: Grain boundaries; Varistors; Piezoelectric effects; Schottky barriers; Current density
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Nonmetallic-Inorganic Materials
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 14 Sep 2015 12:31
Official URL: http://dx.doi.org/10.1063/1.4929360
Identification Number: doi:10.1063/1.4929360
Funders: This work was financed by the Deutsche Forschungsgemeinschaft (DFG) under the Project No. RO954/23
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