ZnO压敏陶瓷冲击老化的电子陷阱过程研究

Research on electronic process of impulse degradation of ZnO-based ceramics

使用8/20μs脉冲电流发生器对普通商用ZnO陶瓷压敏电阻片进行了最多5000次的冲击试验.测量了冲击前后试样的电气性能和介电特性,分析了冲击后小电流区的U-I特性和损耗角正切值tanδ随脉冲大电流的不断作用而发生的变化.实验发现压敏电压U1mA随冲击次数的增加经历增大—稳定—减小三个过程.认为正反偏Schottky势垒的中性费米能级的变化是影响样品小电流区的最根本原因.本文提出用试样的非线性系数α作为老化特征参数比传统的U1mA能更好地表征其老化程度;发现在-100℃时,冲击600次后介电频谱中在105Hz附近出现新的损耗峰,该损耗峰的活化能随冲击次数的增大而降低,最后趋于稳定,认为该冲击老化过程中出现的新峰是由晶界中的陷阱俘获和发射注入的电子所引起.

The electrical and dielectric properties of a commercial ZnO-based varistor ceramics were measured in the process of 8 /20 μs impulse current degradation up to 5000 times of impulses. The characteristics of U-I in the region of low current and the loss tangent were mainly investigated. It was found that the varistor voltage U1mA will first increase rapidly with impulse times increasing,and then remain stable and finally decrease sharply. Furthermore,a new loss peak emerges at-100℃ in the dielectric spectra after 600 times of impulse degradation,which suggests a new trapping behavior introduced in the degradation process. Activation energy of the new peak first decreases,then becomes independent on impulse times. It was also found that the non-linear coefficient was more sensitive to the degradation process than varistor voltage U1mA. These phenomena have not been reported before,which revealed that the variation of the neutral Fermi level between positive bias Schottky barrier region and reverse bias Schottky barrier region is the origin which leads to the degradation of electrical properties.