This study presents a bias-crystallization mechanism (BCM) that is based on ZnO/In/ZnO tri-layer film and thermal annealing treatment on ZnO/ITO/ZnO tri-layer films. After biasing (40 V, 0.025 A), the resistivity of the ZnO/In/ZnO sample was reduced to 1.35 x 10(-2) Omega cm. Bias-induced Joule heat and indium ion diffusion were critical factors with regard to decreasing resistivity. When substituted for the metal indium layer, the ZnO/ITO (13 nm)/ZnO thin film demonstrated comparatively better electrical properties and optical transmittance. During thermal annealing, the indium and tin atoms in the ITO structure diffused into the ZnO matrix and improved the conductivity of the tri-layer film. Inter-metallic oxide (IMO) was formed in the interface between the ZnO and the interlayer, and it dominated the crystallization characteristics as well as the optical and electrical properties of the tri-layer films. (C) 2013 Elsevier B.V. All rights reserved.