Reversible transition between the polar and antipolar phases and its implications for wake-up and fatigue in HfO2-based ferroelectric thin film

Abstract

Atomic-resolution Cs-corrected scanning transmission electron microscopy revealed local shifting of two oxygen positions (OI and OII) within the unit cells of a ferroelectric (Hf0.5Zr0.5)O2 thin film. A reversible transition between the polar Pbc21 and antipolar Pbca phases, where the crystal structures of the 180° domain wall of the Pbc21 phase and the unit cell structure of the Pbca phase were identical, was induced by applying appropriate cycling voltages. The critical field strength that determined whether the film would be woken up or fatigued was ~0.8 MV/cm, above or below which wake-up or fatigue was observed, respectively. Repeated cycling with sufficiently high voltages led to development of the interfacial nonpolar P42/nmc phase, which induced fatigue through the depolarizing field effect. The fatigued film could be rejuvenated by applying a slightly higher voltage, indicating that these transitions were reversible. These mechanisms are radically different from those of conventional ferroelectrics.

Structural and Electrical Response of Emerging Memories Exposed to Heavy Ion Radiation

“…This improvement can be a result of the beam-induced reduction of the monoclinic phase initially present in as-grown films. Such a recovery of ferroelectric properties induced by cycling has been reported in literature for fatigued, nonirradiated PZT 69 and HfO xbased 70 ferroelectric films. Additionally, a comparable enhancement of the polarization in HfO 2 thin films by light ion He bombardment was recently reported.…”

Memory Window Enhancement in Antiferroelectric RAM by Hf Doping in ZrO₂

“…AFE behavior is frequently attributed to a reversible fieldinduced phase transition from the tetragonal to orthorhombic phase, though there is recent evidence of an antipolar Pbca phase [16], [17]. The gradual evolution from AFE to FE properties with more Hf content in Zr 1-x Hf x O 2 is indicative of a compositionally tunable first-order phase transition [18], [19] that is consistent with the free energy diagrams in Fig.…”

Nanocrystallite Seeding of Metastable Ferroelectric Phase Formation in Atomic Layer-Deposited Hafnia–Zirconia Alloys

“…The pristine state is defined as the state of the as-fabricated capacitor subjected to two voltage cycles. The pinched P – V loop can be due to an antiferroelectric behavior, which is attributed to the T-phase or orthorhombic Pbca phase of HZO, or domain pinning in a ferroelectric O-phase film…”

“…The pristine state is defined as the state of the as-fabricated capacitor subjected to two voltage cycles. The pinched P−V loop can be due to an antiferroelectric behavior, which is attributed to the T-phase 13 or orthorhombic Pbca phase 15 of HZO, or domain pinning in a ferroelectric Ophase film. 21 As the ALD temperature increases from 200 to 250 °C, the wake-up behavior is greatly suppressed, and the P−V loops measured for the 225 and 250 °C ALD samples display little or no antiferroelectric behavior.…”

“…Other advanced material characterization techniques demonstrated to identify the O/T-phases are based on the local structures of the crystal phases. For example, Cheng et al reported observation of different orthorhombic phases (space groups Pbc 2 1 and Pbca ) and T-phase ( P 4 2 / nmc ) in crystallized HZO films using annular bright-field scanning transmission electron microscopy (ABF-STEM), showing O atomic positions in different crystal structures. McBriarty et al utilized extended X-ray absorption fine structure spectroscopy to distinguish the O-( Pca 2 1 ) and T-phase in bilayer HfO 2 –ZrO 2 films, determining the phase distributions by fitting the Hf and Zr edge absorption spectra by simulated data.…”