We present the oxygen ion drift-based resistive switching features of TiOx/TiOy bi-layer homo-junctions. The TiOx layer in this bi-layer configuration was designed to have a stoichiometric chemical composition of TiO2, while the TiOy layer was designed to have a non-stoichiometric chemical composition. X-ray photoelectron spectroscopy measurements were carried out before and after electro-forming to determine the role of non-lattice oxygen content. Variation of the oxygen ion content in the TiO2 layers resulted in changes in the on/off ratio and increased the non-lattice oxygen content. A possible switching mechanism based on oxygen ion content is discussed. (C) 2013 Elsevier B. V. All rights reserved.