Anisotropic Charge Diffusion in Polar-Layered Oxides for Ultralong Charge Retention

Persistent surface charge retention in dielectric oxides is critical for a wide range of electronic and energy applications, including charge-trapping memory devices, triboelectric generators, and supercapacitors. Since charge retention is intrinsically governed by charge diffusion, understanding and controlling the underlying diffusion mechanisms in charge-storing materials remain significant challenges. Here, ultralong charge retention in epitaxially grown LaAlO₃ (LAO) thin films is reported, enabled by anisotropic charge diffusion. The surface accumulation of oxygen vacancies, driven by the internal polar field, effectively suppresses out-of-plane electron hopping, allowing ≈90.9% of the initially injected charges to remain on the LAO surface after 180 h, with stable retention persisting for weeks or longer. Time-resolved Kelvin probe force microscopy and finite-difference simulations consistently reveal that this retention enhancement arises from diffusion anisotropy induced by surface-localized defect states in LAO, rather than by isotropic ionic migration. These results provide an effective strategy for designing high-performance charge storage materials based on polar-layered oxides, paving the way for durable surface charge-based electronic and energy devices.