Ultra-thin ferroelectrics

Device applications of ferroelectrics have not only utilized the switchable polarization but also adopted myriads of emerging physical properties. In particular, ferroelectrics in ultra-thin limit have recently attracted considerable scientific and technological interest owing to the increasing demand for miniaturization of electronic devices. In the last two decades, ultra-thin ferroelectrics have rapidly developed with the advances in the theoretical calculations, synthesis, and characterization techniques. However, atomic-scale realization and rigorous characterization of ultra-thin ferroelectricity remain challenging. In this review, we summarize state-of-the-art researches on ultra-thin ferroelectrics. We provide a brief overview of the history and underlying mechanism of ferroelectrics in the context of ultra-thin ferroelectrics. In particular, we discuss complex transition metal oxide ultra-thin ferroelectrics, ferroelectric two-dimensional materials, and fluorite HfO2-based ultra-thin ferroelectrics. Further, we discuss the characterization techniques used to verify the ultra-thin limit of ferroelectricity, followed by device applications based on various emergent properties of ultra-thin ferroelectrics. Finally, we provide a brief conclusion and outlook.