Pulse-Programmed Short-Term Plasticity and Long-Term Potentiation of MoS2 Memristive Devices

Short-term plasticity (STP) and long-term potentiation (LTP) properties of neural synapses are crucial for developing complex neuromorphic systems and functions. In this work, we fabricated two-terminal memristors with multi-layer MoS2 channels and investigated pulse-programmed short-term and long-term synaptic responses. This work indicates that MoS2 memristors exhibit different magnitudes of STP and LTP effects under different pulse programming settings. Specifically, we utilized the paired-pulse facilitation (PPF) function for fitting experimentally measured relaxation curves of MoS2 memristors to quantitatively evaluate the relative dominance of STP and LTP effects. Such analytic results show that the absolute magnitudes of both STP and LTP effects in a memristor increase with increasing pulse frequency, pulse voltage (or amplitude), pulse duty cycle, and a total number of applied pulses, whereas the relative dominance levels of these two effects are typically not in a simple monotonous relationship with these pulse parameters. This indicates that the programming pulse parameters profoundly affect pulse-field-mediated charge trapping and S-vacancy migration processes which are responsible for the observed STP and LTP effects, respectively. This work provides a useful guideline for activating STP and LTP effects in emerging memristive devices based on 2D layered semiconductors, which could be deployed for making synaptic nodes in hardware-based artificial neural networks or neuromorphic sensory devices capable of sensing spatiotemporal events.