Reversible Negative Resistive Switching in an Individual Fe@Al₂O₃ Hybrid Nanotube for Nonvolatile Memory

Hybrid nanostructures can show enormous potential in different areas because of their unique structural configurations. Herein, Fe@Al₂O₃ hybrid nanotubes are constructed via a homogeneous coprecipitation method followed by subsequent annealing in a reducing atmosphere. The introduction of zero band gap Fe nanocrystals in the wall of ultrawide band gap Al₂O₃ insulator nanotubes results in the formation of charge trap centers, and correspondingly a single hybrid nanotube-based two-terminal device can show reversible negative resistive switching (RS) characteristics with symmetrical negative differential resistance (NDR) at relatively high operation bias voltages. At a large bias voltage, holes and electrons can be injected into traps at two ends from electrodes, respectively, and then captured. The bias voltage dependence of asymmetrical filling of charges can lead to a reversible variation of built-in electromotive force, and therefore the symmetrical negative RS with NDR arises from two reversible back-to-back series bipolar RS. At a low readout voltage, the single Fe@Al₂O₃ hybrid nanotube can show an excellent nonvolatile memory feature with a relatively large switching ratio of ∼30. The bias-governed reversible negative RS with superior stability, reversibility, nondestructive readout, and remarkable cycle performance makes it a potential candidate in next-generation erasable nonvolatile resistive random access memories.