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

Tingfeng Song,Ignasi Fina,Florencio Sánchez

doi:10.1063/5.0083661

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.

Highlights

Renewed interest in ferroelectric materials for memory applications has been triggered by the discovery of ferroelectricity in HfO2 films,1 which are compatible with CMOS technology
These results contribute to the fundamental understanding of the switching dynamics in ferroelectric hafnium oxide and are relevant for applications
Fast switching is only observed when the final polarization state is aligned with the imprint field

Summary

Introduction

Renewed interest in ferroelectric materials for memory applications has been triggered by the discovery of ferroelectricity in HfO2 films, which are compatible with CMOS technology. CMOS compatibility makes ferroelectric HfO2 interesting for memory applications, such as non-volatile random access memories and field effect transistors. Contrary to what is commonly found in archetypical ferroelectric materials where ferroelectric properties degraded while reducing thickness to the nanoscale, ferroelectric hafnium oxide shows stable ferroelectric character in films thinner than around 10 nm. This robustness for very thin films makes HfO2 especially suitable for its integration in ferroelectric tunnel junctions.13,14Polarization switching dynamics characterization is extremely relevant for applications and to understand the underlying mechanisms of ferroelectric switching. CMOS compatibility makes ferroelectric HfO2 interesting for memory applications, such as non-volatile random access memories and field effect transistors.. Contrary to what is commonly found in archetypical ferroelectric materials where ferroelectric properties degraded while reducing thickness to the nanoscale, ferroelectric hafnium oxide shows stable ferroelectric character in films thinner than around 10 nm.. Contrary to what is commonly found in archetypical ferroelectric materials where ferroelectric properties degraded while reducing thickness to the nanoscale, ferroelectric hafnium oxide shows stable ferroelectric character in films thinner than around 10 nm.6–12 This robustness for very thin films makes HfO2 especially suitable for its integration in ferroelectric tunnel junctions.. In recent years, switching dynamics has been characterized in ferroelectric polycrystalline HfO2 films having different dopant atoms.. In recent years, switching dynamics has been characterized in ferroelectric polycrystalline HfO2 films having different dopant atoms. Commonly, it is found that the characteristic switching time is in the range of 500–1000 ns.

Methods

Results

Conclusion