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There are unrevealed factors that bring about the performance variations of resistive switching devices. In this work, Pt/CeO x /Pt devices prepared by magnetron sputtering showed rectification in their asymmetrical current–voltage (I–V) curves during voltage sweeps. X-ray photoelectron spectroscopy showed that the deposited CeO x film had an inhomogeneous composition, and more oxygen vacancies existed in CeO x near the top electrode. The asymmetrical resistance change of the Pt/CeO x /Pt devices can be explained by the presence of more charged oxygen vacancies in CeO x near the top electrode, along with the Schottky conduction mechanism. This work reveals that the compositional inhomogeneity is inevitable in the magnetron sputtering of oxide targets like CeO2 and can be an important source of device-to-device and cycle-to-cycle variations of memristors.

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TiN/HfO2/ Ce O x /TiN memristors were prepared by magnetron sputtering. To further improve their performance, the devices were rapidly thermally annealed at different temperatures for different times. Compared with those of unannealed devices, the coefficients of variation (CVs) of the set voltage ( V SET ) and the reset voltage ( V RESET ) were reduced by 35.1% and 59.4%, respectively, and the CVs of the resistances in low and high resistance states ( R LRS and R HRS ) were reduced by 70.2% and 52.7%, respectively, after annealing at 400°C for 2 min in air. Through X-ray diffraction, X-ray photoelectron spectroscopy, and I ‐ V curves of the devices before and after annealing, we propose that the combined effect of grain growth (i.e., grain boundary reduction) and decreased oxygen vacancy content in the switching film resulting from annealing is responsible for the improvement in the switching parameter distribution of TiN/HfO2/ Ce O x /TiN devices. This work presents a simple way to enhance the performance of memristors.