Microstructural Change in Crystal Grains during Phase Transformation of Hf-Zr-O Ferroelectric Thin Films

摘要

Phase transformation of Hf-Zr-O films with the annealing condition is investigated. It is shown that depending on the thermal budget applied to the Hf-Zr-O films, the transformation of crystal structures progresses in the order of the tetragonal phase, the orthorhombic phase, and finally the monoclinic phase. This trend is reflected on the emergence of ferroelectricity in Hf-Zr-O films. The stabilization of the metastable orthorhombic phase before transforming into the most stable monoclinic phase is discussed based on the mechanical stress caused by the volume change between crystal cells. Its evidence is demonstrated as the change of microstructure in the crystal grains.