All-Oxide ITO/HZO/WO x Ferroelectric Tunnel Junctions with Oxygen-Engineered Interfaces for Highly Endurable Neuromorphic Computing

Ferroelectric tunnel junctions (FTJs) are promising synaptic devices for neuromorphic computing owing to their compact two-terminal structure and ability to support multilevel conductance modulation. However, many FTJ synapses rely on complex multilayer stacks or additional insertion layers to stabilize interfacial transport, increasing device complexity and limiting scalability. Here, we demonstrate a structurally simple metal-ferroelectric-metal (MFM) FTJ based on an ITO/Hf₀.₅Zr₀.₅O₂/WO_x stack in which the interface and electrode properties are deliberately engineered to achieve stable switching without additional layers. By tuning the oxygen stoichiometry of the WO_x bottom electrode, a controlled trap-rich interfacial region is formed that enables polarization-modulated trap-assisted tunneling. In addition, the use of an ITO top electrode redistributes the electric field across the junction, improving programming reliability and breakdown tolerance. As a result, the optimized FTJ exhibits a resistance ratio of ∼100, switching endurance exceeding 10⁸ cycles, and 64 well-resolved conductance states. The device further demonstrates stable spike-dependent plasticity and reliable analog weight modulation suitable for neuromorphic operation. Neural-network simulations based on experimentally extracted conductance characteristics achieve 91.5% accuracy on the MNIST data set, highlighting the potential of simple MFM FTJ synapses for scalable neuromorphic and in-memory computing hardware.