Ferroelectricity in HfO₂ and related ferroelectrics

抄録

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 Hf_0.5Zr_0.5O₂ 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 YO_1.5–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.