Gate-Deterministic Remote Doping Enables Highly Retentive Graphene-MXene Hybrid Memory Devices on Plastic

In this work, a highly retentive and synaptic-functional transistor memory device architecture based on the gate-deterministic remote doping of graphene via surface-oxidized Ti₃C₂T_X MXene nano-floating-gates (NFG) is presented. By using solution-phase size-sorting followed by controlled surface oxidation process, a regulated distribution of MXene nanoflakes comprising metallic Ti₃C₂T_X as the core surrounded by TiO₂-a high dielectric constant insulator-as the shell is achieved. The size-sorted core/shell-like MXene nanoflakes show a self-sustainable charge trapping/detrapping behavior, which is highly feasible for realizing non-embed NFGs for transistor memory devices. Interestingly, unlike the conventional NFG-embedded architecture, the introduction of core/shell-like MXene under an electrolyte-gated graphene field-effect transistor (GFET) architecture induces a cooperative evolution of the hysteresis loop associated with ionic motion in the electrolyte gates and charge trapping/detrapping in the nanoflakes, resulting in a deterministic remote doping of the graphene layer. The resulting device exhibited a highly retentive memory behavior, which can be optimized by the nanoflake size distribution. In addition, synaptic functions having mechanical flexibility can be successfully emulated using MXene-based GFETs fabricated on a flexible polyethylene naphthalate substrate.