Abstract
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.
Highlights
Investigations concerning oxygen deficiency will increase our understanding of those factors that govern the overall material properties
Ferroelectric HfO2 is considered an alternative to ferroelectric perovskites because of its compatibility with current complementary metal–oxide–semiconductor (CMOS) technologies and high scalability
The extremely weak interaction between ferroelectric dipoles was attributed to the flat ferroelectric phonon, which is a unique character of HfO2-based ferroelectricity[27]
Summary
Investigations concerning oxygen deficiency will increase our understanding of those factors that govern the overall material properties. We report the oxygen- deficiency induced enhancement of ferroelectric switching properties of Si-doped HfO2 thin films. A Monte Carlo simulation for the variation in the energy barrier of the polarization flipping confirmed the increase of characteristic switching speed Defects, such as oxygen deficiencies, are present in all material systems and are generally considered detrimental to performance. The control of oxygen stoichiometry has been considered a promising way to manipulate the functionality of ferroelectric oxides, such as incipient ferroelectricity[6], stabilization of intermediate polarization states[7], and defect-mediated polarization switching[8,9]. Robust subloop polarization stability of the ferroelectric H fO2 film has been reported for deterministic control of memory states for analog devices[24,25]. These causalities in HfO2 itself and the consequent emergence of ferroelectricity have been pursued to understand the underlying mechanism of ferroelectricity more precisely
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