Ultrathin, dense, high purity, stoichiometric HfO2films were grown by plasma-enhanced atomic layer deposition from TEMAH and O2plasma at a substrate temperature of 300°C. Utilizing these high quality HfO2thin films of precise thickness enabled an accurate study of the effect of the thickness of the oxide, i.e., 5 nm and 8 nm HfO2, and the oxygen exchange layer (OEL), i.e., 5 nm and 10 nm Ti, on the electroforming and resistive switching performance. A thinner oxide layer and a thicker OEL, respectively, resulted in a reduction of the electroforming voltage due to an easier formation of the conductive filament. In addition, differences in the bipolar type resistive switching behavior of various HfO2/Ti cells were observed and a transition into complementary switching was found for the stack built with 8 nm HfO2and 5 nm Ti.