Epitaxial ferroelectric Hf0.5Zr0.5O2 thin film on a buffered YSZ substrate through interface reaction

In this study, we used pulsed laser deposition to successfully grow epitaxial Hf0.5Zr0.5O2 (HZO) films on (001)-, (011)- and (111)-oriented yttria-stabilized zirconia (YSZ) substrates using TiN as the bottom electrode. It is found that the TiO2 buffer layer formed by the interface reaction is the key to epitaxial growth. The epitaxial HZO films (∼15 nm in thickness) exhibit ferroelectric behaviour with a remnant polarization of 7–30 μC cm−2 and a coercive field of 1.1–2.3 MV cm−1. Using piezoresponse force microscopy, polar domains can be written/read and reversibly switched with a phase change of 180° in all the films. X-ray diffraction and high-resolution transmission electron microscopy reveal the presence of nano domains, and a clear epitaxial relation among different layers whose interfaces are relaxed by reconstruction. X-ray absorption spectroscopy provides deep insight into the microstructural origin of ferroelectricity in HZO. A large interface strain stabilized ferroelectric state is observed which is manifested as the non-centrosymmetric Pca21 phase.