Large remanent polarization in Ta-doped HfO2 thin films by reactive sputtering

Applied Physics Letters, Volume 119, Issue 4, July 2021. Ta-doped HfO2 thin films grown on Pt/Ti/SiO2/Si by reactive sputtering possess strong ferroelectric properties, as detected by corresponding polarization vs electric field measurement and mesoscopic piezoresponse force microscopy. Capacitance/current-electric field curves are used to reveal the substances with ferroelectric properties in the thin films. The ferroelectricity of Ta-doped HfO2 is influenced by Ta contents. The remanent polarization Pr can reach ∼53 μC/cm2 by optimizing the Ta percentage. X-ray diffraction and Raman scattering analyses indicate only the presence of monoclinic phase peaks in undoped HfO2 thin films, while Ta doping promotes the formation of the ferroelectric phase (orthorhombic Pca21). X-ray photoelectron spectroscopy demonstrates that the incorporation of Ta5+ within the HfO2 lattice boosts the ferroelectric properties. A polydomain structure is observed on the bare surface of 16% Ta-doped HfO2. Moreover, the switching behavior of the domain is explored by applying an external voltage, demonstrating the potential for storage device applications.