Anisotropic Resistive Switching in NiO Thin Films Deposited on Stepped MgO Substrates

Duisebayev T. Zhazitov M. Abdullah M. Tezekbay Y. Syrlybekov A. Ibraimov M. Khaniyev B. Serikov T. Nuraje N. Toktarbaiuly O.
November 2025 Multidisciplinary Digital Publishing Institute (MDPI)

Nanomaterials
2025 #15 Issue 22

Thin films of nickel oxide (NiO) were deposited on a 5° miscut magnesium oxide (MgO)(100) substrate using electron-beam evaporation to pursue morphology-directed resistive switching. The atomic force microscope (AFM) confirmed a stepped surface with a terrace width of ~85 nm and a step height of ~7 nm. After deposition, the film resistance decreased from 200 MΩ to 25 MΩ by annealing under ambient air at 400 °C, attributed to the increase in the p-type conductivity through nickel vacancy formation. Top electrodes of Ag (500 nm width, 180 nm gap) were patterned parallel or perpendicular to the substrate steps using UV and electron-beam lithography. Devices aligned parallel to the step showed reproducible unipolar switching with 100% yield between forming voltages 20–70 V and HRS/LRS~10² at ±5 V. In contrast, devices formed perpendicular to the steps (8/8) subsequently failed catastrophically during electroforming, with scanning electron microscopy (SEM) showing breakdown holes on the order of ~100 nm at the step crossings. The anisotropic electrodynamic response is due to step-guided electric field distribution and directional nickel vacancy migration, illustrating how substrate morphology can deterministically influence filament nucleation. These results highlighted stepped MgO as a template to engineer the anisotropic charge transport of NiO, exhibiting a reliable ReRAM as well as directional electrocatalysis for energy applications.

anisotropic switching , nickel oxide , resistive random-access memory , stepped MgO substrate

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National Laboratory Astana, Nazarbayev University, Astana, 010000, Kazakhstan
Department of Physics and Technology, Al-Farabi Kazakh National University, Almaty, 050040, Kazakhstan
Institute of Molecular Nanophotonics, Buketov Karaganda University, Karaganda, 100024, Kazakhstan
Department of Chemical & Materials Engineering, School of Engineering & Digital Science, Nazarbayev University, Astana, 010000, Kazakhstan
TEQNOVATE LLC, Astana, 010000, Kazakhstan

National Laboratory Astana
Department of Physics and Technology
Institute of Molecular Nanophotonics
Department of Chemical & Materials Engineering
TEQNOVATE LLC

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