Low‐Temperature‐Sputtered Epitaxial WO ₃ Bottom Electrodes for Reliable Interfacial Memristive and Neuromorphic Devices

Advances in emerging non‐volatile memories demand electrode materials that are complementary‐metal‐oxide‐semiconductor (CMOS) compatible and form atomically smooth, chemically well‐defined interfaces while enabling controlled interfacial oxygen exchange with switching layers. However, few materials simultaneously satisfy these requirements. Here, we demonstrate back‐end‐of‐line (BEOL) compatible, epitaxial WO ₃ thin films sputter‐deposited at 400 °C as viable binary‐oxide bottom electrodes. To benchmark structural quality, WO ₃ deposited at 500 and 700 °C was used as references, confirming that high‐quality epitaxial growth with smooth interfaces and low defect density can be achieved at BEOL‐compatible conditions. By employing chemically similar electrode and switching materials to minimise interfacial mismatch and promote stable oxygen‐vacancy (V _o ) exchange, memristors are fabricated using Hf‐doped WO ₃ (WHO) switching layers. These devices show electroforming‐ and current‐compliance‐free interfacial switching, operating voltages ≤±4 V, high resistance uniformity, memory‐switching ratios >130 and endurance >5 × 10 ³ cycles. They further demonstrate multiple stable conductance states and linear, symmetric analogue potentiation and depression modulation. The analogue behaviour originates from combined trap‐assisted electronic conduction and field‐driven V _o redistribution across an abrupt WHO/WO ₃ interface. This work establishes low‐temperature‐grown epitaxial WO ₃ as a reliable platform for integrating oxide electrodes into non‐volatile memory and neuromorphic electronics.