Homo-layer hafnia-based memristor with large analog switching window

The fast development of high-accuracy neuromorphic computing requires stable analog memristors. While filamentary memory switching is very common in binary oxides, their resistive switching usually involves abrupt changes due to the rupture or reformation of metallic filaments. In this work, we designed a memristor consisting of dual-layer HfOy/HfOx, with different concentrations of oxygen vacancies (y > x). During the electroforming process, both the migration of existing oxygen vacancies in HfOx and the generation of new oxygen vacancies in HfOy occur simultaneously, leaving a semiconducting part close to the HfOy/HfOx interface. The resulting filament is not metallic as a whole, as revealed by first principles calculations. Such a device demonstrates excellent switching uniformity as well as highly gradual resistance change, ideal for neuromorphic computing. Through fine tuning of the filament structure, the device achieves low variation, high speed, gradual SET and RESET processes, and hundreds of stable multi-level state behaviors. The long-term synaptic plasticity was further achieved, showing good linearity and large analog switching window (ΔG as high as 487.5 μS). This works affords a route toward a gradual resistance change in oxide-based memristors.