Electrical Surface Breakdown of Thin-Film ZNO Varistors

Samples of zinc oxide varistor material representing a thin film are studied. An electrical discharge is consistently produced at electric field strengths and energy levels both well below those required to cause bulk material with the same composition to fail. The investigation examines each of the major issues which could be responsible for this anomalous behavior. Electrode/sample contact integrity, electrode shape, and surface considerations are studied. It is concluded that the discharge is directly related to the surface preparation. Study of the sample surface under different preparation conditions indicates that macroscopic as well as microscopic surface properties influence the behavior of the discharge.