Quantized synaptic characteristics in HfO2-nanocrystal based resistive switching memory

We demonstrate the reliable resistive switching performance of nanocrystalline-HfO2 inside amorphous-HfOx in TaN/nc-HfO2/ITO memristor structure. Transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were utilized to confirm the presence of nc-HfO2 and non-stoichiometric HfOx in the switching layer. In presence of nc-HfO2, quantized conductance was controlled by the narrowing of conductive filaments in an atomic scale applying a very slow voltage sweep. Conductance change under DC voltage shows the quantized conductance states with integer and half-integer multiples of G0 (77.5 μS). Enhanced resistive switching performances with multilevel resistance states behavior were investigated under different current compliance and RESET stop voltages. Short-term plasticity and long-term potentiation, pulse number, and spike rate-dependent plasticity by controlling the magnitude and duration of the input stimulus play a critical role in modulating the post-synaptic conductivity. The combination of nc-HfO2 and amorphous-HfOx in the memristor structure provide promising scope for neuromorphic system applications