Atomic-scale characterization of defects generation during fatigue in ferroelectric Hf_0.5Zr_0.5O₂ films: vacancy generation and lattice dislocation

Abstract

For the first time, we directly observed the lattice dislocation and monoclinic (m-) phase formation in ferroelectric Hf <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf> Zr <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (HZO) films during fatigue, through the spherical aberration (Cs)-corrected transmission electron microscopy (TEM) technique. The main observations are: 1. More oxygen vacancies (Vo) tend to be generated when the orthorhombic (o-) phase polar axis is close to the out-of-plane direction (parallel to the electrical field); 2. The o-phase with large grain size tends to fragment with lattice dislocation and m-phase formation by martensitic-like transformation; 3. At the interface of m-/o-structure, the Vo formation energies are lowered. This work provides fundamental understanding on the defect generation mechanism of HZO film at the atomic-level, laying a solid foundation to further optimization and commercialization of the ferroelectric HZO devices.