Effects of heat treatment and in situ high-temperature X-ray diffraction study on the formation of ferroelectric epitaxial Y-doped HfO2 film

The process of forming the ferroelectric orthorhombic phase was investigated for epitaxial 7% Y-doped (YHO7) films using in situ high-temperature X-ray diffraction. Epitaxial YHO7 films were grown on (111) ITO-coated (111)YSZ substrates by pulsed laser deposition at room temperature and a subsequent heat treatment process. Films deposited at room temperature were crystallized as paraelectric monoclinic phase. The monoclinic phase partially changes to tetragonal phase above 600 degrees C and perfectly transformed around 950 degrees C during heating. The change from tetragonal phase to orthorhombic phase was detected at 300 degrees C, corresponding to the Curie temperature under the cooling process. These results clearly suggest that the tetragonal phase was more stable at 1000 degrees C for YHO7 films on heating than the other phases, and the formation of this tetragonal phase-the high-temperature paraelectric phase of the ferroelectric orthorhombic phase-is key to the formation of the ferroelectric orthorhombic phase. (C) 2019 The Japan Society of Applied Physics