Unraveling the Effects of Depolarization in Ultrathin Barium Titanate

ABSTRACT

Depolarization fields pose a critical obstacle to realizing ultrathin ferroelectric devices with low‐voltage operation. Although the phenomenology of depolarization has been observed for decades, whether polarization loss proceeds through suppression of ferroelectric order or reverse‐domain formation has remained unresolved. Here, a combination of experiment and simulation resolves this question and establishes the electrostatic origin of polarization instability in the ultrathin limit for BaTiO ₃ . Synchrotron X‐ray absorption spectroscopy confirms that the polar structural distortion in persists down to (at least) 3 nm even as the remanent polarization falls sharply, identifying reverse‐domain formation as the primary mechanism of polarization loss. Time‐resolved pulsed‐switching measurements reveal dynamically evolving depolarization fields that converge to a thickness‐independent equilibrium value. An electrostatic model attributes these fields to the effective series capacitance of the electrode interfaces, validated through thickness scaling and dielectric‐buffer experiments. Phase‐field simulations reveal that modifying this series capacitance reshapes switching dynamics by redistributing internal fields without altering the intrinsic ferroelectric energy landscape. Defects play a consequential secondary role, independently controlling relaxation pathways within this electrostatically constrained regime. These results establish depolarization as a system‐level effect governed by heterostructure boundary conditions, and identify interfacial design and defect management as complementary strategies for stabilizing polarization in ultrathin ferroelectrics.