The authors systematically studied reactive sputtering deposition of TiOx thin films using a mixture of Ar and O2 gases under different ratios of O2 flow. As directly revealed by X-ray photoelectron spectroscopy, the deposition changed from a metallic Ti target mode to an oxide target mode when the O2 flow ratio was beyond 40%, resulting in TiOx thin films with different chemical compositions. Consequently, metal/oxide/metal devices with a single TiOx layer exhibited a broad spectrum of electrical characteristics such as Ohmic, rectifying, and memristive behavior. The reactive sputtering deposited TiOx thin films were also used in a bilayer memristive device structure, and a transition from bipolar to unipolar switching behavior was observed for devices based on thin films prepared with different oxygen flow.