Investigations concerning oxygen deficiency will increase our understanding of those factors that govern the overall material properties. Various studies have examined the relationship between oxygen deficiency and the phase transformation from a nonpolar phase to a polar phase in HfO2 thin films. However, there are few reports on the effects of oxygen deficiencies on the switching dynamics of the ferroelectric phase itself. Herein, we report the oxygen- deficiency induced enhancement of ferroelectric switching properties of Si-doped HfO2 thin films. By controlling the annealing conditions, we controlled the oxygen deficiency concentration in the ferroelectric orthorhombic HfO2 phase. Rapid high-temperature (800 °C) annealing of the HfO2 film accelerated the characteristic switching speed compared to low-temperature (600 °C) annealing. Scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) revealed that thermal annealing increased oxygen deficiencies, and first-principles calculations demonstrated a reduction of the energy barrier of the polarization flip with increased oxygen deficiency. A Monte Carlo simulation for the variation in the energy barrier of the polarization flipping confirmed the increase of characteristic switching speed.

We report variations in the characteristic ferroelectric switching time and interface free carrier concentration associated with wake-up and split-up behaviors of a 4.2 mol. % Si-doped HfO2 thin film. Prior to the development of the split-up behavior, the thin films exhibited the wake-up behavior; the remanent polarization increased on repeated electric field cycling. After the wake-up behavior, Si-doped HfO2 films exhibited degradation of the remanent polarization values and splitting of the ferroelectric switching current peaks when a lower electric field was swept; this is referred to as the split-up behavior. An investigation of the ferroelectric switching dynamics revealed retardation, followed by recovery, of the characteristic switching time for ferroelectric nucleation, coincident with the wake-up and split-up behaviors, respectively. We analyzed the interface free carrier concentration from capacitance–voltage characteristics and revealed that the wake-up and split-up behaviors were associated with changes of numbers of defects as electric field cycling continued.

We report the effect of 60Co gamma-ray irradiation on the ferroelectric properties of metal–ferroelectric Hf0.5Zr0.5O2–metal thin film structures. The pristine Hf0.5Zr0.5O2 films showed strong radiation tolerance against gamma-rays with stable remanant polarization values. When Hf0.5Zr0.5O2 films were exposed to electric field cycling, or “wake-up” process, prior to irradiation, however, their ferroelectricity demonstrated a clear degradation of remanant polarization and coercive voltage shift of the hysteresis curves. The analysis of ferroelectric switching dynamics revealed faster polarization switching with broadening of Lorentzian distribution of characteristic switching time for higher radiation doses, which is contrary to the wake-up behavior. The relationship between the wake-up process and gamma-ray irradiation on the stability of ferroelectric Hf0.5Zr0.5O2 films was discussed in light of domain alignment and defect mechanisms, considering both the redistribution and trapping of defect charges.