Reversible Transformation between Bipolar Memory Switching and Bidirectional Threshold Switching in 2D Layered K-Birnessite Nanosheets.

Birnessite-related manganese dioxides (MnO) have recently been studied owing to their diverse low-dimensional layered structures and potential applications in energy devices. The birnessite MnO possesses a layered structure with edge-shared MnO octahedra layer stacked with interlayer of cations. The unique layered structure may provide some distinct electrical properties for the 2D layered nanosheets. In this work, layered K-birnessite MnO samples are synthesized by a hydrothermal method. The resistive switching (RS) devices based on single K-birnessite MnO nanosheets are fabricated by transferring the nanosheets onto SiO/Si substrates through a facile and feasible method of mechanical exfoliation. The device exhibits nonvolatile memory switching (MS) behaviors with high current ON/OFF ratio of ∼2 × 10. And more importantly, reversible transformation between the nonvolatile MS and volatile threshold switching (TS) can be achieved in the single layered nanosheet through tuning the magnitude of compliance current (). To be more specific, a relatively high (1 mA) can trigger the nonvolatile MS behaviors, while a relatively low (≤100 μA) can generate volatile TS characteristics. This work not only demonstrates the memristor based on single birnessite-related MnO nanosheet, but also offers an insight into understanding the complex resistive switching types and relevant physical mechanisms of the 2D layered oxide nanosheets.