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

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Abstract
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/Hf $_{\text{0.5}}$ Zr $_{\text{0.5}}$ O $_{\text{2}}$ (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 (Ta $_{\text{2}}$ O $_{\text{5{\kern-0.2pt}-\textit{x}}}$ ) with doubly positively charged oxygen vacancies $^{^{^{^{}}}}$ (V $_{\text{o}}^{{++}}$ ). The imprint field increases with increasing HPA temperatures and achieved a high imprint field of 1.65 MV/cm at 600 $^{\circ}$ C. Moreover, endurance was observed up to 10 $^{\text{8}}$ cycles without a breakdown while maintaining the original coercive fields up to 10 $^{\text{5}}$ 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.
Funding Information
  • National Research Foundation of Korea (NRF-2020M3F3A2A02082436, NRF-2020M3F3A2A01081916, NRF-2020M3F3A2A01081898)

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