Improved resistive switching and synaptic characteristics using Ar plasma irradiation on the Ti/HfO2 interface

In this report we perform the irradiation of argon (Ar) plasma on the surface of amorphous atomic layer deposited HfO2 thin film intentionally to modulate interface between Ti and HfO2 having influence on resistive switching as well as synaptic characteristics within the Ti/HfO2/Pt memristor structure. Due to structural change in sub-TiOx interfacial layer as well as oxygen vacancy modulation at the HfO2/Ti interface, compared to the pristine HfO2 thin film, the Ar plasma-irradiated HfO2 thin film exhibits an electro-forming free repeatable switching with digital SET and multilevel voltage-induced RESET characteristics under smaller positive and negative sweeps, respectively. The multilevel resistance states are induced by applying different stopping voltages during the process of RESET. To investigate synaptic characteristics of the Ar plasma-treated device, we carried out the transient electrical measurement by designing the input stimulation with different pulse parameters in order to achieve the symmetric and near-linear conductance change. Finally, we emulated one of the important learning rules of biological synapse called spike-time-dependent-plasticity (STDP) by applying specially designed spikes at the top and bottom electrode by adjusting the time intervals between pre- and post-spikes. (C) 2019 Elsevier B.V. All rights reserved.