Oxygen Vacancy Control as a Strategy to Enhance Imprinting Effect in Hafnia Ferroelectric Devices

Hafnia-based ferroelectric materials are recently drawing a significant attention for future electronic devices; however, there is a need to further enhance their functionality for practical applications. Especially, an imprinting effect has been regarded as a defect to be reduced in ferroelectrics; yet, it can be positively applied to various electronic devices with the functionality of self-rectifying behavior and threshold voltage adjustment. For the first time, we report a high imprinting effect in bilayer stack capacitors [TiN/Hf0.5Zr0.5O2 (HZO)/tantalum oxide (TaO)/TiN] by employing an optimal TaO insertion layer. Furthermore, the imprinting effect was enhanced by adopting high-pressure annealing (HPA) process. X-ray photoelectron spectroscopy (XPS) depth profile analysis reveals that the origin of the imprint field is the tantalum suboxides (Ta2O5-x) with doubly positively charged oxygen vacancies ( $\text{V}_{\text {o}}^{++}$ ). The imprint field increases with increasing HPA temperatures and achieved a high imprint field of 1.65 MV/cm at 600 °C. Moreover, endurance was observed up to 108 cycles without a breakdown while maintaining the original coercive fields up to 105 cycles. We also investigated how the TaO insertion layer with an imprint field influences the switching, interfacial, and ferroelectric properties. These findings on the imprinting effect provide a new strategy to improve the functionality of hafnia-based ferroelectric devices in the near future.