In situ study of phase transition in HZO ferroelectric thin films via TEM electron beam irradiation

Abstract

Oxygen vacancies (V_O) play a crucial role in the stability of the ferroelectric orthorhombic (o-) phase of hafnium dioxide (HfO₂)-based thin films. However, the stability of the ferroelectric phase of HfO₂ under the action of V_O and the mechanism of ferroelectric phase transition are still unclear. In this work, V_O concentration in Hf_0.5Zr_0.5O₂ (HZO) thin films is tuned through electron beam irradiation inside a transmission electron microscope. For the crystalline HZO thin films processed through rapid thermal annealing, the increase of the V_O concentration during in situ electron beam irradiation facilitated the phase transition from the non-polar monoclinic (m-) and tetragonal (t-) phases to the polar o-phase. For the amorphous HZO thin films, the nucleation and growth process of the m- and o-phases are observed during in situ electron beam irradiation. The phase transition from m-phase to o-phase is accompanied by the evolution from tensile to compressive strain. These results help to clarify the mechanism of ferroelectric phase transition under the action of V_O, and guide the control of the ferroelectric properties and phase stability of HfO₂-based thin films.

Keywords

Ferroelectric film / Hf_0.5Zr_0.5O₂ / oxygen vacancy / phase transition / electron beam irradiation

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