Evolution of the Interfacial Layer and Its Impact on Electric-Field-Cycling Behaviors in Ferroelectric Hf_1–xZr_xO₂

Doped HfO2 thin films, which exhibit robust ferroelectricity even with aggressive thickness scaling, could potentially enable ultralow-power logic and memory devices. The ferroelectric properties of such materials are strongly intertwined with the voltage-cycling-induced electrical and structural changes, leading to wake-up and fatigue effects. Such field-cycling-dependent behaviors are crucial to evaluate the reliability of HfO2-based functional devices; however, its genuine nature remains elusive. Herein, we demonstrate the coupling mechanism between the dynamic change of the interfacial layer and wake-up/fatigue phenomena in ferroelectric Hf1–xZrxO2 (HZO) thin films. Comprehensive atomic-resolution microscopy studies have revealed that the interfacial layer between the HZO and neighboring nonoxide electrode experienced a thickness/composition evolution during electrical cycling. Two theoretical models associated with the depolarization field are adopted, giving consistent results with the thickening of the interfacial layer during electrical cycling. Furthermore, we found that the electrical properties of the HZO devices can be manipulated by controlling the interface properties, e.g., through the choice of electrode match and hybrid cycling process. Our results unambiguously reveal the relationship between the interfacial layer and field-cycling behaviors in HZO, which would further permit the reliability improvement in HZO-based ferroelectric devices through interface engineering.