Electrical properties of Al2O3-doped ZnO varistors prepared by sol–gel process for device miniaturization

Al2O3-doped ZnO varistors with high performance have been fabricated with nano composite powders, which were prepared by the sol–gel method. The xerogels, calcined powders and sintered material ceramics were fully characterized. The electrical properties and grain boundary characteristics were measured. The average grain size decreased from 4.4 μm to 3.0 μm and the breakdown voltage increased from 720 V/cm to 1160 V/cm as the amount of Al2O3 increased from 0.0 wt.% to 0.40 wt.%. 2 ms square-wave test indicates that the energy capability was better in a sol–gel derived ZnO varistor than a conventional sample and was enhanced by Al2O3 doping. Improved electrical properties of sol–gel derived ZnO varistors is attributed to the smaller grain size and more uniform distribution of additives. Al2O3-doped ZnO varistor obtained from sol–gel process is useful for device miniaturization.