Evaluation of Planar-Type Thin Film ZnO Varistors Fabricated Using Pulsed Laser Ablation

Abstract

Planar-type thin film Bi-Mn-Co-doped ZnO varistors were fabricated on a silica glass substrate or a sintered alumina substrate using a visible light (532 nm) pulsed laser ablation method. The deposited thin films were annealed at 800°C or 900°C in air. For the thin films deposited on alumina substrates and then annealed, the contents of Bi and Mn decreased compared with those of the as-deposited films. Voltage-current (V-I) characteristics of the thin-film varistor fabricated on the alumina substrates and annealed showed nonlinearity. The nonlinearity index α was approximately 10 for the thin film deposited on the alumina substrate and annealed at 800°C in air using a target of ZnO doped with 2.5 mol% Bi2O3, 0.5 mol% MnO2 and 0.2 mol% Co3O4. Moreover, the current density of 20 A/cm3 was relatively high for safety use.