Infrared Micrograph of a ZnO Varistor During Electrical Breakdown

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  Diff. and Therm. Prop. Group
  High Temperature Materials Laboratory
  Metals and Ceramics Division
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    H. Wang, R.B. Dinwiddie, HTML
    F.A. Modine et. al., Solid State Division, ORNL

Background

ZnO varistors are used as surge protectors due to the non-linear I-V characteristic. Topics such as conducting paths, breakdown mechanisms, barrier height have been covered extensively. However, there has been no experimental technique to make the electrical breakdown visible. Working with the Solid State Division, HTML staff used an infrared camera to capture the heat transient associated with the breakdown.


Results

The thermal micrograph was captured by a high-speed, high-sensitivity IR camera, 1 ms after a 1 A electrical pulse. The integration time was 1 ms. The specimen was 100 µm thick and 4mm wide. The grain size ranged from 100 µm to 250 µm. Electrical breakdown occurred at selected paths with small Schottky barrier potentials, and appeared as hot conducting paths in the IR image. The bright spots indicated local heating at grain boundaries.

Publications

"Non-uniform heating in ZnO varistors studied by infrared imaging and computer simulation", H.Wang, M. Bartkowiak, F.A. Modine, R.B. Dinwiddie, L.A. Boatner and G.D. Mahan, J. Am. Ceram. Soc., 81(8) pp 2013-2022 (1998)


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Acknowledgments

URL: http://www.html.ornl.gov/tpuc/varistor.html