Electrically Driven Ion Dynamics with Negative Differential Resistance in Alkali Ions Intercalated 2D-Layered Metal Oxide

Ion-based electronics provide a platform to explore unique physical properties and have extensive applications in the design of bio-nano interface and bio-mimetic devices. 2D-layered materials, thanks to their ability to easily accommodate ions between their layers, emerge as an ideal choice for these ion-based electronic platforms. To realize systematic ion control in 2D-layered materials, it’s crucial to ensure stable spatiotemporal reactions of ions on demand. However, substantial hurdles persist during device fabrication and operation based on ion intercalation, including the need for external force during the intercalation process, the challenge of maintaining thermodynamic stability with ions, and the management of structural distortions during ion migration. Here, we introduce the intrinsic stable potassium ion (K⁺) intercalated 2D-layered MnO₂ (2D K-MnO₂) by the metal-organic chemical vapor deposition (MOCVD) method. Thermodynamically, the layered structure of MnO₂ with the intercalated potassium ion and H₂O has the lowest Gibbs free energy among the other phases, resulting in spontaneous intercalation during the growth process. Potassium ions intercalated into the van der Waals gap of layered MnO₂ can easily move under the external bias, and this electrical-driven ion movement causes the reversible phase transition to Mn₃O₄. Especially, the phase transition of Mn₃O₄ and the lattice distortion by over-concentrated potassium ions form a high Schottky barrier that presents dominant negative differential resistance (NDR). We designed a device with multi-channels of the 2D K-MnO₂ to apply simultaneous signals with various conditions and successfully proved that the spatial and temporal potassium ion controls the gradual conductance changes with NDR behavior. Moreover, we imitated the biological voltage-gated potassium channels based on NDR-related conductance change and applied the long-term & short-term plasticity to the associative learning. Our approach to NDR-based ionic motion of 2D K-MnO₂ shows not only a new concept of the dynamics of ion devices but also the high applicability for ionic activities in the human body.