Impact of non-ferroelectric phases on switching dynamics in epitaxial ferroelectric Hf0.5Zr0.5O2 films

Abstract

Determining the switching speed and mechanisms in ferroelectric HfO2 is essential for applications. Switching dynamics in orthorhombic epitaxial ferroelectric Hf0.5Zr0.5O2 films with either significant or negligible presence of monoclinic paraelectric phase is characterized. Switching spectroscopy reveals that the polarization dynamics in pure orthorhombic ferroelectric phase films can be modeled by the Kolmogorov-Avrami-Ishibashi mechanism with large characteristic time (≈1 μs), which is shortened in fatigued junctions. The long switching time indicates that non-archetypical switching mechanisms occur and that ionic motion or other extrinsic contributions might be at play. Films containing a higher amount of paraelectric monoclinic phase show a shorter switching time of 69 ns, even in pristine state, for applied electric field parallel to the imprint field, enabling synaptic-like activity using fast electric stimuli. Thus, the presence of defects or paraelectric phase is found to improve the switching speed, contrary to what one can expect a priori.