We have found a memristive characteristic of an amorphous Ga-Sn-O (α-GTO) thin-film device with double layers of different oxygen density. The double layers are deposited using radio frequency (RF) magnetron sputtering, whose gas for the lower layer contains less oxygen, whereas that for the upper layer contains more oxygen, and it is assumed that the former contains more oxygen vacancies, whereas the latter contains fewer vacancies. The characteristic is explained by drift of oxygen and is stable without forming operation because additional structures such as filament are unnecessary. The fabrication is easy because the double layers are successively deposited simply by changing the oxygen ratio in the chamber.
