Ferroelectric Hf0.5Zr0.5O2 films with improved endurance obtained through low temperature epitaxial growth on seed layers

Abstract

Crystallization temperature is a critical parameter in the stabilization of the metastable ferroelectric phase of HfO₂. The optimal crystallization temperature used for polycrystalline films is too low to grow epitaxial films. We have developed a new growth strategy, based on the use of an ultrathin seed layer, to obtain high-quality epitaxial films of orthorhombic Hf_0.5Zr_0.5O₂ at a lower temperature. The threshold temperature for epitaxy is reduced from about 750 °C to about 550 °C using a seed layer. Epitaxial films deposited at low temperatures exhibit highly enhanced endurance, and films grown at 550-600 °C show high polarization, no wake-up effect, and greatly reduced fatigue and improved endurance in comparison with the films deposited at high temperatures without a seed layer. We propose that the endurance enhancement is due to a positive effect of the defects, which limits the propagation of pinned ferroelectric domains.