Low-temperature-sputtered Epitaxial WO3 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 WO3 thin films sputter-deposited at 400 °C as viable binary-oxide bottom electrodes. To benchmark structural quality, WO3 deposited at 500 and 700 °C were 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 (Vo) exchange, memristors are fabricated using Hf-doped WO3 (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 × 103 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 Vo redistribution across abrupt WHO/WO3 interface. This work establishes low-temperature-grown epitaxial WO3 as a reliable platform for integrating oxide electrodes into non-volatile memory and neuromorphic electronics.