Deterministically Controllable Multi‐State Ferroelectric Switching in BiFeO ₃ Thin Films Through Atomic Interface Design

Realization of multiple ferroelectric states with distinct polarization values is a promising pathway to achieve next‐generation nonvolatile high‐density memory. However, deterministically achieving stable multi‐state polarization is challenging owing to the inherent bi‐stable nature of ferroelectric polarization vectors and the stochastic nature of domain nucleation and growth during the polarization switching. Here, we demonstrate the atomic‐termination‐engineered electric‐field‐controlled deterministic and reversible tri‐state polarization switching among the upward state (+ P ), the intermediate state (0), and the downward state (‐ P ) in (001)‐oriented BiFeO 3 thin films epitaxially grown on the engineered SrTiO 3 (001) substrate with periodically self‐assembled SrO and TiO 2 terminations by combining experimental characterization and phase‐field simulations. Such multi‐state switching is enabled by deterministically precise control of volume fraction of the downward and upward domains generated by SrO and TiO 2 terminations, originating from distinct built‐in biased voltages induced by the interface valence mismatch. A wide voltage window (∼1.2 V) for the intermediate state is appealing for multi‐state applications. Our findings suggest a universal fundamental mechanism for a variety of ferroelectric oxides to realize deterministic, controllable, and reversible multi‐state polarization by interfacial termination engineering for high‐density nonvolatile multi‐state ferroelectric memory.