Ex Situ Doping of Oxygen Vacancies for Improved ZnO Resistance Switching Devices

Oxygen vacancies (V_Os) are fundamental for oxide resistance switching (RS) devices, while the introduction of V_Os in oxides during the fabrication processes has generally generated unfavorable defects which have limited the improvements in RS performance. Herein, a novel strategy, called ex situ V_Os doping, has been proposed to increase the concentration of V_Os to fabricate improved ZnO RS devices. The ex situ V_Os doping process is similar to modulation doping of heterojunctions, where V_Os are intentionally incorporated in a separate oxide material and then migrated toward the target materials. Specifically, HfO₂/ZnO architecture with a thin oxygen-deficient HfO₂ capping layer is prepared, where V_Os in the HfO₂ layer facilely migrated toward the underlying ZnO under applying bias. Theoretical calculations and atomic binding energy analysis have verified the effective ex situ V_Os doping of ZnO in the HfO₂/ZnO architecture. Benefiting from the dominant migration of V_Os along grain boundaries, the accumulated V_Os around grain boundaries at HfO₂/ZnO interface provided preferential nucleation sites for deterministic formation of conductive filaments. Accordingly, improved ZnO RS devices have been demonstrated in terms of increased RS window and enhanced uniformity, stability, and endurance. The ex situ doping of V_Os using a heterojunction architecture enables multi-dimensional regulation of the formation of conductive filaments, which will find potential applications in achieving improved oxide RS devices in the future.