The effects of annealing and wake-up cycling on the ferroelectricity of zirconium hafnium oxide ultrathin films prepared by remote plasma atomic layer deposition
Journal
Smart Materials and Structures
Journal Volume
28
Journal Issue
8
Date Issued
2019
Author(s)
Abstract
Abstract The crystalline phases and ferroelectric properties of Zr x Hf 1- x O 2 (ZHO) ultrathin films (5.6–5.8 nm in thickness) prepared by remote plasma atomic layer deposition (RP-ALD) before and after post-annealing and wake-up cycling have been investigated in this study. For the films with high ZrO 2 percentages, the plasma bombardment from RP-ALD was able to induce partial ferroelectric orthorhombic ( o ) crystallization during the film deposition stage. The as-deposited pure ZrO 2 ultrathin film exhibited a fully developed ferroelectric polarization hysteresis after wake-up cycling. For the films containing the ferroelectric o -phase in the as-deposited state, post-annealing the films followed by a wake-up cycling procedure could greatly promote ferroelectric switching while maintaining low leakage. The ferroelectric properties of the ZHO ultrathin films were highly dependent on the ZrO 2 -to-HfO 2 ratio and could be tailored by various combinations of post-annealing and wake-up cycling. An increase in the amount of HfO 2 has been found to be detrimental to the ferroelectricity, mainly due to the high crystallization temperature of HfO 2 . For the post-annealed ZHO ultrathin films, the ferroelectricity was governed by the relative amounts of the ferroelectric o -phase and the non-ferroelectric monoclinic ( m ) phase. The Zr 0.5 H 0.5 O 2 ultrathin film was the only composition which exhibited a large, stable polarization hysteresis after post-annealing but before wake-up cycling. The annealed Zr 0.5 H 0.5 O 2 ultrathin film is believed to contain a suitable mix of o and m phases to produce loose grain boundaries, allowing the ferroelectric o -phase crystallites to switch freely under electrical loading.
Publisher
Institute of Physics Publishing
Type
journal article