Tuning the Transport Properties of Artificial Synapses: A DFT-Supported Experimental Approach*

Defect engineering is an essential aspect of resistive switching (RS) memories. This work illustrates cationic dopant (Ni) controlled RS characteristics in the thin film of anatase titanium dioxide (A-TiO₂). A significant increase in ON/OFF ratio to 10³ with a gradual change in resistance state is accomplished and such RS characteristics are highly expedient for neuromorphic computing applications. Detailed investigations by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) as well as density functional theory (DFT)-based first-principles calculations establish the role of Ni in memristive operation. In particular, TEM results show an evolution of two different Ni-concentration regions within the films that help to reduce the host Ti-site from its +4 valence state, as obtained from Ti-2p XPS analysis. This claim is further verified by DFT calculations, showing a change in the charge density near the Ni-site form the Bader charge analysis and electron localisation function (ELF) plots. Moreover, the role of those two Ni-concentration regions in regulating transport properties of the Au/ Ni:A-TiO₂ /Pt devices similar to the biological synapse is discussed.