Toward Highly Pure Ferroelectric Hf1-xZrxO2 Thin Films by Tailoring the Strain in an Unstable Thermodynamic System

Yu-Cheng Kao^1*, Hao-Kai Peng², Kuo-An Wu¹, Yung-Hsien Wu², Pin-Jiun Wu³

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
²Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan
³National Synchrotron Radiation Research Center, Hsinchu, Taiwan

* Presenter:Yu-Cheng Kao, email:peter62602@gapp.nthu.edu.tw

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

Keywords: ferroelectric material, crystal polymorphism, X-ray diffraction, X-ray absorption, residual strain