HfON-Based Optoelectronic Memristor for Synaptic Computing

In this study, we investigate resistive switching, positive photoconductivity, and synaptic properties of a transparent bilayer memristor. An optically transparent (~90%) memristor is fabricated using optimized thicknesses for HfON and TiOx layers. By introduction of oxygen and nitrogen gas mixture, HfON is fabricated by reactive sputtering, which is identified using X-ray photoelectron spectroscopy (XPS) depth spectra. Such memristor exhibits stable low-resistance state (LRS) and high-resistance state (HRS) of over $10^{{4}}$ cycles at 0.1 V. By changing compliance current and reset stop voltage, multilevel cell (MLC) characteristic is achieved. The nonlinearity values for potentiation and depression of the memristor are 2.38 and 0.97, respectively. The conduction mechanism for the memristor is explained using band diagrams. Under the illumination of blue light, the memristor displays positive photoconductivity. Multiple resistive states are achieved by changing illumination time intervals and intensities. For synaptic behaviors, the learning and forgetting behaviors of human brain are mimicked using the optical pulse of 10 and 20 s as spikes. Paired pulse facilitation (PPF) is calculated using electrical and optical pulses to demonstrate that this memristor would be a promising candidate for optoelectronic synaptic systems.