Atomic visualization of the emergence of orthorhombic phase in Hf0.5Zr0.5O2 ferroelectric film with in-situ rapid thermal annealing

For the first time, the dynamic process of orthorhombic (o-) phase emergence during rapid thermal annealing in polycrystalline Hf 0.5 Zr 0.5 O 2 (HZO) ferroelectric film was directly visualized though in-situ spherical aberration corrected transmission electron microscopy technique. We have the following main observations: (1) o-phase nucleates from centrosymmetric tetragonal (t-) phase at top TiN/HZO interface where the oxygen vacancy (Vo) concentration is rich, identifying that Vo is helpful to lower the free energy of o-phase; (2) o-phase appears in both heating up and cooling down stages. The o-phase formed in the heating stage rapidly transforms into t-phase again as the temperature further increasing, and the one formed in the cooling stage is retained. These findings provide solid evidence on the o-phase origin in fluorite-type ferroelectric materials.