Toward Highly Pure Ferroelectric Hf_1–xZr_xO₂ Thin Films by Tailoring the Strain in an Unstable Thermodynamic System

By utilizing the combined analyses of X-ray diffraction and X-ray absorption spectroscopy, a systematic identification on the crystal phases of the polymorphic Hf1–xZrxO2 thin films with various series of preparation conditions was presented. The results of the rigorous quantitative analysis show that the monoclinic phase and the tetragonal phase are mutually exclusive and a high fraction of orthorhombic phase up to 97% can be achieved under a specific process condition. On the basis of the observed correlation between the phase fraction and the in-plane strain, the strain-induced activation energy barrier was proposed to clarify the mechanism of the kinetic phase transition process. The endurance test of the device, exhibiting that the wake-up degree (remnant polarization variation ΔPr/Pmax) increases exponentially with increasing the content of tetragonal phase in the pristine state, indicating the transition from tetragonal to orthorhombic as a possible mechanism of the wake-up effect. Our study presented herein points the way to efficiently optimize the strain toward highly pure orthorhombic Hf1–xZrxO2 thin film through precisely controlling the process parameters, which is beneficial for the future development of ferroelectric devices.