A Study on the Impact of Oxygen Vacancy Engineering on the Ferroelectric Properties and Device Performance of HZO Thin Films

Abstract

Hafnium zirconium oxide (HZO) has emerged as a promising ferroelectric material for next- generation non-volatile memory, particularly Ferroelectric Tunnel Junctions (FTJs), due to its CMOS compatibility, strong ferroelectricity at nanometer-scale thicknesses, and suitability for three- dimensional integration. Despite these advantages, the electrical performance of HZO is highly sensitive to oxygen stoichiometry. Oxygen vacancies (Vo) can act as parasitic leakage paths, distorting polarization switching, while insufficient vacancies may limit the stabilization of the orthorhombic ferroelectric phase. Consequently, careful control of oxygen content is critical for achieving reliable, high-performance HZO-based devices. In this work, HZO thin films were systematically engineered by adjusting the H2O pulse time during Atomic Layer Deposition (ALD) to control oxygen vacancy concentration. Three sets of films—Ref HZO, +O HZO, and ++O HZO—were analyzed to understand how oxygen vacancy affects ferroelectric property and leakage behavior. The Ref HZO exhibited elevated leakage current and a rounded P–V hysteresis loop, indicating leakage-assisted polarization and reduced switching reliability. In contrast, the oxygen-rich ++O HZO displayed sharp hysteresis loops, distinct switching current peaks, and sufficiently high remnant polarization, consistent with a higher ratio of the orthorhombic phase. These results highlight the importance of an optimized oxygen vacancy concentration in stabilizing the ferroelectric phase and improving ferroelectric property. The effect of oxygen stoichiometry on device performance was further examined using FTJs. Devices based on Ref HZO showed high off current (Ioff) due to defect-mediated tunneling, which degraded the Tunneling electroresistance (TER). By contrast, ++O HZO FTJs exhibited lower Ioff and substantially improved TER, demonstrating that better stoichiometry enhances the tunneling barrier and overall switching performance. These findings also demonstrate a key trade-off in FTJs: the oxygen vacancy concentration that maximizes polarization is not necessarily optimal for TER, underscoring the need to tailor oxygen vacancy according to the specific device function. Finally, 3D Metal-Ferroelectric-Metal (MFM) devices were fabricated to probe the intrinsic ferroelectric property. P–V and I–V measurements confirmed that the trends observed in thin-film studies were preserved, demonstrating that careful vacancy engineering improves ferroelectric switching while suppressing leakage. The established link between H2O pulse time, oxygen vacancy concentration, orthorhombic phase formation, and electrical performance provides a solid foundation for optimizing both planar and 3D HZO devices. Overall, this study demonstrates that oxygen vacancy control is a key process variable for enhancing ferroelectric properties, minimizing leakage, and improving device performance. These insights offer practical guidelines for designing high performance FTJs and 3D MFM devices, while providing a material basis for next-generation ferroelectric memory applications.