Ligand Exchange Reaction Enables Digital‐To‐Analog Resistive Switching and Artificial Synapse within Metal Nanoparticles

Abstract

AbstractThe transition between digital and analog resistive switching in a single memristive device is beneficial for the reduction in power consumption and circuit complexity, the development of in‐memory neuromorphic computing, and the discovery of new switching mechanisms. However, achieving such transition is a challenge due to the complex switching mechanisms and device designs. Here, it is shown that the digital‐to‐analog resistive switching can be realized by the ligand exchange reaction of metal nanoparticles. The field‐injected copper cations migrate within carboxyl‐functionalized gold nanoparticle (AuNP) layer that are subsequently reduced into metallic filaments, enabling an abrupt resistive switching. Importantly, when the carboxyl groups on the gold nanoparticle are replaced by amino‐carboxyl ligands, the copper cations coordinate with the new ligands and create the conductance bridges to reduce the electron tunneling/hopping energy barriers, leading to continuous modulation in conductivity. This analog resistive switching allows to implement several important synaptic functions such as potentiation/depression, paired‐pulse facilitation, learning behaviors including forgetting curves and spaced learning effect. In the end, due to the non‐volatile characteristics, the gold nanoparticle synapse is used to build single layer perceptron for pattern classification with 100% accuracy.