Elektro-mechanische Charakterisierung von Varistoren

Translated title of the contribution: Electro-mechanical characterisation of ZnO-Varistors

Martin Stoiser

Research output: ThesisDiploma Thesis

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Abstract

Varistor ceramics are resistors with highly non-linear electrical characteristics. These functional ceramics are widely used in parallel with circuits to protect devices from voltage surge. Varistors are made of polycrystalline zinc oxide (ZnO), made semiconducting by addition of several dopants. Dopant ions, which are situated at the grain boundary interface, trap electrons, what leads to the formation of potential barriers. The current flow through the bulk is limited by these electrostatic barriers, the so-called Double Schottky Barriers (DSB). When mechanical stress is applied to ZnO, additional piezoelectrical charges are induced at the DSB, which causes a change of the electrical characteristics (i.e. “piezotronic” effect). The modification of the characteristic I-V-curves of Multilayer Varistors (MLV) in respect to uniaxial applied compressive stress is subject to this thesis. The impact of the piezoelectric effect is investigated in detail by a variation of testing setups with respect to the orientation of the electrical field vector and the applied load. For the first time micro four point probe measurements on single grain boundaries in combination with applied tensile as well as compressive stresses are performed. In a special preparation process thin sections of MLV are bond to ceramic cantilevers. A micro four point bending stage is used for compressive or tensile loading of the cantilever and to transfer the mechanical strain to the thin section. The macroscopic compressive stress tests clearly show drifts of the I-V-curves and also modifications of the natural asymmetry, both caused by the “piezotronic” effect. The electro-mechanical microscopic investigations on single grains reconfirm the detected effects. The tendency of a measured drift under compressive stress goes into reverse when tensile stress is applied.
Translated title of the contributionElectro-mechanical characterisation of ZnO-Varistors
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Supancic, Peter Hans, Supervisor (internal)
Award date1 Jul 2016
Publication statusPublished - 2016

Bibliographical note

embargoed until null

Keywords

  • Double Schottky Barrier (DSB)
  • Varistor
  • Piezoelectricity
  • Piezotronic effect
  • Micro 4 Point Probe
  • Multilayer-varistors
  • MLV

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