Vacancy-Assisted Polarization-Catastrophe Framework for Wake-Up and Ferroelectricity in Hafnium Oxide.

Abstract

Ferroelectric wake-up in hafnium oxide remains one of the key unresolved problems in oxide electronics. Here, we combine four-dimensional scanning transmission electron microscopy (4D-STEM), X-ray photoelectron spectroscopy (XPS), first-principles calculations, electrical characterization, and theoretical modeling to investigate wake-up in TaN/Hf0.5Zr0.5O2/TiN capacitors. Although the remanent polarization increases by approximately 2.6-fold after wake-up, the orthorhombic phase fraction changes only slightly from 20.3% to 21.4%, indicating that structural evolution alone cannot explain the electrical activation. XPS and first-principles calculations reveal that the ferroelectric response is highly sensitive to oxygen-vacancy configuration. Motivated by these observations, we develop a vacancy-assisted polarization-catastrophe framework in which vacancy ordering renormalizes the dipolar interaction and drives the transition from a nonpolar single-well to a ferroelectric double-well energy landscape. The model quantitatively explains the observed enhancement of polarization, switching current, capacitance, and hysteresis, establishing vacancy ordering as the governing mechanism of wake-up in hafnium oxide.