HfO ₂ -based memristive synapses with asymmetrically extended p-n heterointerfaces for highly energy-efficient neuromorphic hardware

The escalating energy consumption of existing artificial intelligence hardware has become a serious global issue that demands immediate action. Neuromorphic computing offers promises to drastically reduce this footprint. Here, we introduce multicomponent p-type Hf(Sr,Ti)O₂ thin films for energy-efficient, resistive switching-based neuromorphic devices. We demonstrate interfacial memristors with ultralow switching currents (≤~10^-8 A), exceptional cycle-to-cycle and device-to-device uniformities, and retention >10⁵ s. They reveal hundreds of ultralow conductance levels with a modulation range of >50 (without reaching any saturation) and reproducibly satisfy unsupervised learning rules. This performance originates from incorporating a self-assembled p-n heterointerface between p-type Hf(Sr,Ti)O₂ and n-type TiO_xN_y, resulting in a fully depleted space-charge layer asymmetrically extended into Hf(Sr,Ti)O₂, a large built-in potential, and extremely low saturation current density under reverse bias. Ultralow conductance modulation is controlled by tuning p-n heterointerface's energy-barrier height through electro-ionic charge migration. This materials-engineering strategy addresses energy consumption and variability in existing memristors, opening a pathway toward energy-efficient neuromorphic computing systems.