Structures, varistor properties, and electrical stability of ZnO thin films

In this letter, we report the structures, varistor properties, and electrical stability of ZnO thin films deposited by the gas discharge activated reaction evaporation (GDARE) technique. The X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements showed that the thin films thus prepared have polycrystalline structures with the preferred orientation along the (002) plane whose surface consists of ZnO aggregates with sizes of 50-200 nm. The ZnO thin films deposited by GDARE and annealed at 250 degrees C for 2 h have strong nonlinear varistor-type I-V characteristics. The nonlinear coefficient (alpha) of a single-layered ZnO thin film sample was 33 and that of a triple-layered sample obtained by the many-time deposition was 62. The varistor voltages (V-1mA) of the two samples are found rather close each other. Under a DC bias of 0.75 V-1mA and a temperature of 150 degrees C these thin films exhibit good electrical stability with a degradation rate coefficient K-T of 0.05 mA/h(1/2). (C) 2009 Elsevier B.V. All rights reserved.