Stoichiometric single-crystalline TiO2 thin films were grown on SrTi0.99Nb0.01O3 (Nb:STO) substrates by oxygen plasma-assisted molecular beam epitaxy. The Pt∕TiO2∕Nb:STO∕Pt devices showed extremely weak resistance switching hysteresis without applying reverse bias. However, when the reverse bias increased above −2V, the hysteresis became more and more prominent. Further, it was found that the low (high) resistance state can be set by applying sufficient reverse (forward) bias. The origin of the reverse-bias-induced bipolar switching behavior should be attributed to the modulation of Schottky-like barrier width by electrochemical migration of oxygen vacancies.

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