The effect of Nb doping on the resistance switching characteristics of NiOx films was investigated. Pt/Nb-doped NiOx/Pt metal-insulator-metal stacks were fabricated using NiOx films with various Nb contents sputtered by reactive dc magnetron sputtering. The resistance switching behaviors of the metal-insulator-metal stacks were then examined in conjunction with a study on the physical properties such as the chemical bonding of NiOx films. Nb doping of NiOx at a T-dep of 400 degrees C and an O-2 partial pressure of 5% resulted in an improved endurance of SET/RESET processes with a narrower distribution of V-SET, and a larger memory window compared to undoped NiOx films. NiOx with 5.47% Nb deposited at an O-2 partial pressure of 15% showed bistable resistance switching behavior while undoped NiOx material, deposited under the same condition did not. A study of the chemical bonding states by X-ray photoelectron spectroscopy showed that the Nb-doping of NiOx films produced an increase in the density of Ni-0 and a reduction in the density of Ni3+, compared to corresponding values for undoped NiOx films deposited under the same condition. The resistive switching behavior of NiOx was enhanced by defect engineering with metal impurity with different oxidation valence. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.