Papers by Author: Sayuki Sawa

Abstract: Laminar-type thin-film ZnO varistors were fabricated on sintered alumina substrates using visible light (532nm) pulsed laser deposition (PLD). The structure of the laminar-type thin-film varistor is Ni / Co-added ZnO / impurity layer / Co-added ZnO / Ni. Many droplets were observed on the deposited Bi2O3+MnO2 compared with the deposited Co-added ZnO thin film. Moreover, for droplets on the Bi2O3+MnO2 layer, the content of Mn was higher than that of Bi. The V-I characteristics of the deposited ZnO+CoCl2 or Bi2O3+MnO2 thin film were ohmic. However, V-I characteristics of laminar-type thin film including the Bi2O3+MnO2 impurity layer deposited for 30min showed nonlinearity. The non linearity index α was approximately 2 and the varistor voltage was approximately 1V. Thermal annealing in N2 gas atmosphere at 700°C for 10 min was carried out to improve the crystallinity of the thin film. After annealing, both the varistor voltage and the current at which nonlinearity appeared decreased. Moreover, the value of non linearity index α was approximately 2.8.

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.