Jpn. J. Appl. Phys. 40 (2001) pp. 3606-3609 |Next Article| |Table of Contents|
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Evaluation of ZnO Varistors by Photoacoustic Spectroscopy
Yasuhiro Ohbuchi,
Akitsugu Kimura,
Toshio Kawahara,
Jun Morimoto and
Taro Toyoda1
Department of Materials Science and Engineering, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka 239-8686, Japan
1Department of Applied Physics and Chemistry, The University of Electro-Communications,
1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan
(Received November 23, 2000; accepted for publication January 17, 2001)
ZnO varistors degraded under various conditions were evaluated by photoacoustic spectroscopy (PAS). The degradation where the grain boundary is damaged by DC bias stress is more than that by AC bias stress. PAS, however, reveals that the interior of the grains of the sample degraded by AC bias stress is much more damaged than that by the DC bias stress. The PA signal intensity at a wavelength of more than 500 nm increases and the dispersion of the spectrum decreases throughout the wide wavelength range considered with the degradation time. In particular, the decrease of the spectral dispersion below 500 nm is caused by the change of the electronic states at the interface, that is, the increase of the recombination center of the space charge. The annealing effect on the degradation of ZnO varistors was also studied. The PA spectrum of the sample annealed in N2 gas corresponds to those of the sample degraded by DC and AC bias stress for a long time. This suggests that the degradation of ZnO varistors is closely related to the release of oxygen from both ZnO grain interior and grain boundaries.
URL:
http://jjap.jsap.jp/link?JJAP/40/3606/
DOI: 10.1143/JJAP.40.3606
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