Varistor Ceramic Fabricated By ZnO Composite Nanopowders And Its Degenerative Mechanism And Stability

In order to study the feasibily of Varistor ceramic prepared by sol-gel method and composite nanopowders, the sintered kinetics of the composite nanopowders, the microstructure and the electrical properties of varistor ceramics prepared by composite nanopowders; to study the degradation mechanism of mini-varistor thin piece under DC, AC, pulsed electric field and temperature fields; and to study the stability and the reliability of mini-varistor thin piece. First, A principle of preparetion composite nanopowders by sol-gel method has been preposed, and the physical properties of composite nanopowders has been indicated. Then, A surface diffusion transmission model at the beginning of the grain growing is proposed, on this basis, A kinetics model of grain growing is established, and then the two kinds of materials' microstructures and electrical properties prepared by composite nanopowders and composite micropowders were compared.In the research about mini-varistor device stability and reliability , first, the degradation phenomenon of the mini-varistor thin pieces under AC, DC,pulsed electric fields and temperature fields were investigated, then by the semiconductor Schttky Barrier model; the semiconductor atomic defect model; and the grain boundary depletion layer ion migration model, the degradation phenomenons are explained. On the basis of these, the practical measure of increasing varistor thin piece stability was perpormed.During the study about long time stability and reliability of mini-varistor thin piece, by the deep level transient spectroscopy, mobile defect -Zinc interstitials defect is comfirmed, it is the key factor of device instsbility. Then, by atomic defectmodel, and by defect diffusion and subsequent chemical reaction model, the essence of the stability increasing during heat treatment is expressed. On the basis of these, a compound model was proposed that has made important effect for the varistor stability e.g. grain boundary phase transform from ft into y, and interstitials Zn Znt diffus from depletion layer to grain boundary interface.At the last, in order to exploit low voltage large surge current chip multi-layer type varistor, we cooperate with Hong Chuan Electronics Technical Corporation and has producted two sets of and tens type of chip varistors, that has filled blank of this field in our country; and now, it is our target to realize industrialization.