The dual role of 90° domain walls in ferroelectric switching of Hf0.5Zr0.5O2 thin films: Insights from phase-field simulations

The dynamic behavior of ferroelectric domain walls (DWs), particularly both 90° and 180° DWs, is crucial for high-performance HfO2-based ferroelectric devices. However, fundamentally understanding DW dynamics is challenging because the role of 90° DWs and their interplay with 180° DWs in ferroelectric switching remains elusive in HfO2-based ferroelectrics. Here, we employ phase-field simulations to investigate the dynamics of domain and DW in epitaxial Hf0.5Zr0.5O2 thin films with the coexistence of 90° and 180° DWs. It indicates that the threshold voltage for 90° DW migration is much higher than that for 180° DW owing to the higher migration energy barrier for the former. 90° DWs play a complex dual role in ferroelectric switching: they lower the nucleation voltage by serving as preferential nucleation sites for 180° domain switching, while simultaneously impeding the propagation of 180° DWs due to their high migration energy barrier. Furthermore, 90° DWs guide the switching pathway of nascent 180° domains around ferroelastic domains to avoid the formation of unstable charged DWs. These findings provide a fundamental mesoscale understanding of competitive and synergistic mechanisms between 90° and 180° DWs in ferroelectric switching, offering guidance for precise manipulation of DWs to optimize the performance of HfO2-based ferroelectric memories.