Study On Electrical Transport Properties Of ZnO Based Varistor And Design Of The Varistor With High Peak Current

Zinc oxide varistors with highly nonlinear voltage-current characteristic, excellent surge withstanding capability and wide range working stability are employed to protect electrical circuits in the fields of electrical and electronics. And the research to manufacture ZnO varistor with high peak current has attracted lots of attention both at home and abroad, and has prominent meaning in the future too. In this paper, interface state and electrical transport properties of ZnO varistor at the interface, degradation process under surge, preparation of nano-sized powder and its application in ZnO varistor, sintered process by microwave plasma and oxygen behavior in ZnO varistor are systematically studied, and kinds of models and manufacture process parameters are provided.First of all, the conduction mechanisms such as "Space charge limited current" and "tunneling" are studied. By analyzing the interface defects resulted from dopants and excess Oxygen atom, the trap levels in forbidden band and its distribution are indicated, using instruments tests, for examples: X-ray photoelectron spectroscopy (XPS) and Cathodoluminescence (CL), after that Poisson equation is applied to reason the model of Double Shottky Barrier with some trap states. The degradation mechanism under surge is explained at the same time, especially the effects of distribution of dopants and grain size distribution. After having obtained these conclusions, we design our experiments schedule and contents.The raw materials of ZnO varistors play a very important role to improve the peak current of ZnO varistors, and so three nano-sized raw materials or doping technology are introduced including: A) Sol-Gel method to homogeneously prepare nano-sized compound powder with the same compositions as varistor, B) DC arc plasma to prepare nano-sized Bi2O3 and special doping technology of using metal...