Achieving High ON State Current through Ferroelectric Polarization‐Dependent Interfacial Resistance Switching in Undoped Orthorhombic HfO ₂ Films

ABSTRACT In this work, we report on a ferroelectric tunnel junction based on an epitaxial undoped orthorhombic 3‐nm‐thin HfO 2 film. An OFF/ON resistance ratio of ≈83 and a high ON state current density of ≈5 A/cm 2 , important for fast device readout, is achieved through ferroelectric polarization switching, which causes electron accumulation and depletion in the adjacent LSMO electrode. Oxygen vacancy movement inside the HfO 2 is observed, but plays at most a minor role for switching. The devices show stable switching endurance of over 10 6 switching cycles, low write voltages of ±3 V, both outperforming previous epitaxial HfO 2 FTJs, 16 measured resistance states, and neuromorphic capability by voltage pulse trains and spike‐timing‐dependent plasticity. This strong performance is achieved by designing ferroelectric tunnel junctions at the materials level of undoped HfO 2, which has a higher tunneling probability than HZO and a stabilized oxygen distribution. The resulting device design shows great promise for neuromorphic and analog memory applications.