The electric-pulse-induced resistive switching properties of TiO2, Al2O3, Al2O3/TiO2, and Al2O3/TiO2/Al2O3 thin films were studied by current-voltage (I-V) measurements using Pt/insulator/Ru structures and conductive atomic force microscopy. The switching parameters of the TiO2 film were stable, whereas those of the Al2O3 films show random variations during repeated I-V measurements. Both films show resistive switching by a filamentary switching mechanism with linear conduction behavior in the low V region. The stacked film shows a bias polarity-dependent switching behavior. This suggests that the nucleation of the conducting filaments occurs at the interface where the electrons are injected. (c) 2006 The Electrochemical Society.