The phenomenon of electric field mediated resistance switching in metal oxides is critical to nanoscale electronic devices ranging from conventional energy efficient MOSFETs to emerging memory devices as well as artificial neuron and synaptic devices. Such resistance transition can be facilitated by two main mechanisms: i) conduction of oxygen ions in non-stoichiometric compounds e .g. HfO_x, AlO_x. In this case the redox reaction of the oxide itself is manifested by oxygen anion transport, ii) the oxides serve as electrolyte dielectrics to conduct electrochemically active metal cations, such as Ag or Cu, forming the so-called electrochemical metallization memory (ECM) devices.

So far inert and electrochemically active transition metals such as Pt and Cu/Ag respectively have been implemented to demonstrate resistive switching in Metal-Insulator-Metal (MIM) devices for application in steep slope transistors and as non-volatile memory and selector device. However, post transition metal e. g. Sn with lower cohesive energy as well as lower negative heat of formation of metal oxide offers viable alternative to Cu and Ag in ECM type devices.

In this study, we fabricated asymmetric two terminal MIM structures in a cross-bar array with atomic layer deposited HfO₂ thin film sandwiched between Pt and post-transition metal (Sn). We demonstrate reversible resistance switching in HfO₂. Filamentary conduction by cations beyond a threshold voltage was verified by varying device areas. A recent report demonstrated coexistence of both oxygen anion and metal cation transport being responsible for resistance switching in a single oxide depending on the anode metal. We present a comparative investigation based on current-time (I-t) measurements to distinguish contributions from oxygen anions and metal cations in the resistance switching process.

Using Sn anode we demonstrate bidirectional threshold switching as well as bipolar memory switching. We further evaluate viability of Sn anode in terms of switching speed in comparison with Cu and Ag. Furthermore, we discuss considerations for bidirectional threshold switching and bipolar memory switching with Sn anode substantiated with our ongoing molecular dynamic simulations.