In-situ Observation of Low-Power Nano-Synaptic Response in Graphene Oxide using Conductive Atomic Force Microscopy

Multiple studies have reported the observation of electro-synaptic response in different metal/insulator/metal devices; however, most of them analysed large (>1 m2) devices that do not meet the integration density required by the industry (1010 devices/mm2). Some studies 2 employed a scanning tunnelling microscope (STM) to explore nano-synaptic response in different materials, but in this setup there is a nanogap between the insulator and one of the metallic electrodes (i.e. the STM tip), which is not present in real devices. Here we show how to use a conductive atomic force microscope (CAFM) to explore the presence and quality of nano-synaptic response in confined areas <500 nm2. For this study, we selected graphene oxide (GO) due to its easy fabrication and excellent electrical properties. Our experiments indicate that metal/GO/metal nano-synapses exhibit potentiation and paired pulse facilitation with low write current levels <1 μA (i.e. power consumption ~3 μW), controllable excitatory post-synaptic currents and long-term potentiation and depression. Our results provide a new method to explore nano-synaptic plasticity at the nanoscale, and point GO as an important candidate material for the fabrication of ultra-small (<500 nm2) electronic synapses fulfilling the integration density requirements of neuromorphic systems.