Epitaxial Ferroelectric HfO₂ Films: Growth, Properties, and Devices

About ten years after ferroelectricity was first reported in doped HfO2 polycrystalline films, there \nis tremendous interest in this material and ferroelectric oxides are once again in the spotlight of \nthe memories industry. Great efforts are being made to understand and control ferroelectric \nproperties. Epitaxial films, which have fewer defects and a more controlled microstructure than \npolycrystalline films, can be very useful for this purpose. Epitaxial films of ferroelectric HfO2 have \nbeen much less investigated, but after the first report in 2015 significant progress has been \nachieved. This review summarizes and discusses the main advances on epitaxial HfO2, \nconsidering growth, study of structural and ferroelectric properties, identification of the \nferroelectric phase, and fabrication of devices. We hope this review will help to researchers \ninvestigating epitaxial HfO2. It can also help extend the interest of the ferroelectric HfO2 \ncommunity, now basically focused on polycrystalline samples, to epitaxial films.