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

Oxygen vacancies (VO) 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 VO and the mechanism of ferroelectric phase transition are still unclear. In this work, VO concentration in Hf0.5Zr0.5O2 (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 VO 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 VO, and guide the control of the ferroelectric properties and phase stability of HfO2-based thin films.