Hybrid Ferroelectric Tunnel Junctions with Intrinsic Nonlinearity and Self‐Rectification via Interfacial Reconstruction

Hybrid ferroelectric tunnel junctions (FTJs) that combine large tunneling electroresistance (TER) with intrinsic nonlinearity are attractive for selector‐free memory applications, but practical routes to achieve both functions in a simple device structure remain limited. Here, Pt/Ca‐doped BiFeO 3 (BCFO)/Nb‐doped SrTiO 3 (Nb:STO) FTJs with a metal‐ferroelectric‐metal‐semiconductor configuration are reported, in which post‐growth rapid thermal annealing (RTA) reconstructs the BCFO/Nb:STO interface and induces strongly asymmetric tunneling transport. Pristine BCFO FTJs show the highest TER at a BCFO thickness of 3 nm. After RTA, 4 nm‐thick devices exhibit pronounced rectification and nonlinearity, with a rectification ratio of ∼171, a maximum nonlinearity factor of ∼807, and a TER of ∼10 4 , resulting in a substantial increase in the calculated selector‐free cross‐point array size. Atomic‐resolution analyses reveal an atomically thin reconstructed interfacial layer (RIL) at the BCFO/Nb:STO junction, accompanied by lattice modulation, polarization reversal, cation intermixing, and oxygen‐vacancy redistribution. First‐principles calculations and tunneling simulations indicate that the reconstructed interface reshapes the effective tunneling barrier through localized metallic‐like states and asymmetric band bending. These results suggest a useful design route for converting high‐TER FTJs into intrinsically nonlinear and self‐rectifying tunneling junctions.