"Interfacial Charge Injection and Defect-Dipole Pinning in fe-HZO imprint" 

Fernando Josue Vega, MSE PhD Candidate 

Advisor: Professor Thomas Beechem

Ferroelectric hafnium zirconium oxide (fe-HZO) offers a highly scalable pathway for non-volatile memory architectures, yet its commercial integration remains hindered by reliability issues such as imprint and cycling fatigue. Central to these challenges are oxygen vacancies (VO), which paradoxically help stabilize the ferroelectric phase while simultaneously acting as the primary agents of device degradation. This report untangles the contested physical origins of imprint by dividing literature into driving models, which describe charge movement mechanisms, and effecting models, which describe how the redistributed charge shifts coercive fields. This review also addresses the inherent complexity of the metal-ferroelectric interface, demonstrating that thermodynamic defect generation and the formation of charge reservoirs are heavily dictated by the specific chemistry of the contacting electrodes. We find that the driving model of imprint must change over time from a rapid to a slower mechanism. The effecting mechanism is identified not to be a global internal electric field, but instead the result of localized defect-dipole pinning that emerges from the transient ionization of VO. A gap remains in temporally decoupling the rapid time frame from the slower time frame and determining their respective driving and effecting models. With a thorough baseline understanding of static VO behavior, characterizing dynamic defect generation during field cycling will become significantly simplified. Future work will employ in-situ sub-bandgap photoluminescence and targeted optical acceleration to directly track transient VO charge states in operando. This future work aims to isolate the charge-movement saturation of the initial imprint driving mode to temporally resolve the full evolution of imprint.