Highly Stable Epitaxially Crystallized Ferroelectric Hf_0.5Zr_0.5O₂ Films

Cooling conditions are critical in the crystallization of polycrystalline films of ferroelectric HfO 2 because the energy of the HfO 2 polymorphs is very sensitive to oxygen vacancies and because of the role of kinetics in the stabilization of the metastable orthorhombic phase. Here, we investigate the relevance of cooling conditions in the pulsed laser deposition of epitaxial Hf 0.5 Zr 0.5 O 2 films. The orthorhombic phase crystallized in epitaxial Hf 0.5 Zr 0.5 O 2 films does not change when highly reducing or oxidizing cooling conditions are used. The films exhibit similar ferroelectric properties, including polarization value, absence of the wake-up effect, comparable fatigue, and high retention. These results demonstrate that the phases formed in epitaxial films are highly stable and much less sensitive to cooling conditions than polycrystalline films.