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-TiO_x 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.