Abstract
We report unipolar and bipolar resistive switchings in naturally oxidized AlxO1-x thin films. We find a relationship between the switching behavior and the electrode gap distance. The macro-gap device with the electrode separation of 20 µm shows a unipolar switching behavior while the nano-gap device with the separation of 40 nm shows a bipolar behavior. The result is explained by a model in which the unipolar or the bipolar switching is governed by the way of the carrier injection into oxygen vacancies.