A Multilevel Magnetic Synapse Based on Voltage-Tuneable Magnetism by Nitrogen Ion Migration

Advanced synaptic devices with simultaneous memory and processor capabilities are envisaged as core elements of neuromorphic computing (NC) for low-power artificial intelligence. So far, most synaptic devices are based on resistive memories, where the device resistance is tuned with applied voltage or current. However, the use of electric current in such resistive devices causes significant power dissipation due to Joule heating. Higher energy efficiency has been reported in materials exhibiting voltage control of magnetism (VCM). In particular, voltage-driven ion motion to modulate magnetism (magneto-ionics) is an emerging VCM mechanism that can offer new prospects for low-power implementation of NC. In the present work, voltage-driven nitrogen ion motion is exploited in transition metal nitride (CoFeN) thin films (i.e., nitrogen magneto-ionics) to emulate biological synapses. In the proposed device, distinct multilevel non-volatile magnetic states for analog computing and multi-state storage are realized. Moreover, essential synaptic functionalities of the human brain are successfully simulated. The device exhibits an excellent synapse with a remarkable retention time (≈6 months), high switching ratio and large endurance (≈10³), for hardware implementation of NC. This research provides new insight into exploiting magneto-ionic-based synaptic devices for spin-based neuromorphic systems.