Realization of Long-Term Plasticity in Ion-Gel Gated Monolayer Graphene Synaptic Transistor

The ion-gel gated synaptic transistor has been widely researched to achieve low voltage operation, mimicking synaptic functions for neuro-inspired electronics. Although organic materials have been widely studied for ion-gel gated synaptic transistors, the reliability and retention time of long-term potentiation is still short for neuromorphic computing. To overcome these issues, exploration for new materials in an ion-gel gated synaptic transistor is required. Graphene has been widely studied with various advantages such as zero bandgap property, mechanical flexibility, and biocompatibility.<br/>Here, we fabricated ion-gel gated monolayer graphene synaptic transistors (IG-MGST). Due to ion trapping between graphene monolayer/substrate and ion adsorption on a graphene substrate, various synaptic plasticity long-term plasticity has been realized. Because of the ion-gel gated device, and zero bandgap characteristic of IG-MGST, the device can operate with low voltage consumption with the ambipolar operation. To tune the synaptic plasticity of IG-MGSTs, the ionic size effect of ion-gel has been investigated. Also, Dirac point and resulted operation voltage have been controlled by introduction of various kinds of self-assembled layers. By temperature-dependent plasticity measurement and Raman spectroscopy, the origin of synaptic plasticity has been explored which has not been discovered before. Finally, we simulated the recognition of handwritten digits in both LiTFSI-based ion-gel and [EMIM][TFSI]-based ion-gel, thus improved linearity has been obtained in IG-MGST using LiTFSI-based ion-gel. Our study provides not only a graphene-based synaptic transistor but also provides fundamental information for 2D material-based synaptic transistors for future neuromorphic electronics.