ABSTRACT
Terrace contrast in sectioned zinc oxide (ZnO) varistors observed under scanning electron microscope-remote contact electron beam induced current (SEM-REBIC) has been reported previously and in the past has been proposed as a method for the characterisation of varistor device quality. This chapter presents a simple one dimensional model that attempts to explain the origin of the contrast seen by considering the varistor material as a collection of resistive elements. The model has been used to produce theoretical SEM-REBIC line-scan profiles which show excellent correlation with real-life line-scan and image data for poor quality ZnO varistor material. The model suggests that it may be possible to globally characterize the different contributions to the measured signals, from different zones on the specimen, without the need for examining individual grains or grain boundaries. The observed terraces can extend across several grain widths and are generally aligned in a direction parallel to the remote contacts.
