Ferroelectricity in HfO2 and related ferroelectrics

Ferroelectric HfO2 film has garnered a lot of attention lately due to unique features that cannot be achieved with conventional ferroelectric materials. The ferroelectricity of HfO2 originates from the metastable orthorhombic phase, which does not appear in the phase transition sequence of HfO2 in ambient pressure. This review introduces our recent research on HfO2-related ferroelectrics. The ferroelectric orthorhombic phase was achieved with Hf0.5Zr0.5O2 metal-organic chemical vapor deposition, and obtained by intermediate thermal treatment conditions with low-and high-thermal budget yield in the tetragonal and monoclinic phases, respectively. Furthermore, ferroelectricity was enhanced with the aid of compressive strain, as elucidated by a study using various substrates with different thermal expansion coefficients. Epitaxial films were successfully grown by quenching of a YO1.5-HfO2 solid solution. This epitaxial film revealed that HfO2-related ferroelectrics are good candidates for future integrated application because their ferroelectric properties are comparable to conventional ferroelectric materials. (c) 2018 The Ceramic Society of Japan. All rights reserved.