Nanoscale Investigation of the Effect of Annealing Temperature on the Polarization Switching Dynamics of Hf0.5Zr0.5O2 Thin Films

Abstract

Recently, HfO₂-based ferroelectric thin films have attracted widespread interest in developing next-generation nonvolatile memories. To form a metastable ferroelectric orthorhombic phase in HfO₂, a post-annealing process is typically necessary. However, the microscopic mechanism underlying the effect of annealing temperature on ferroelectric domain nucleation and growth is still obscure, despite its importance in optimizing the operation speed of HfO₂-based devices. In this study, the ferroelectric properties and polarization switching of Hf_0.5Zr_0.5O₂ thin films annealed at different temperatures (550–700 °C) are systematically investigated. Evidently, the crystal structure, remnant polarization, and dielectric constant monotonically change with annealing temperature. However, microscopic piezoresponse force microscopy images as well as macroscopic switching current measurements reveal non-monotonic changes in the polarization switching speed with annealing temperature. This intriguing behavior is ascribed to the difference in the ferroelectric-domain nucleation process induced by the amount of oxygen vacancies in the Hf_0.5Zr_0.5O₂ thin films annealed at different temperatures. This work demonstrates that controlling the defect concentration of ferroelectric HfO₂ by tuning the post-annealing process is critical for optimizing device performance, particularly polarization switching speed.