Phase Transformations Driving Biaxial Stress Reduction During Wake‐Up of Ferroelectric Hafnium Zirconium Oxide Thin Films
Samantha T. Jaszewski, Shelby S. Fields, Sebastián Calderón, Benjamin L. Aronson, Thomas E. Beechem, Kyle P. Kelley, C. Zhang, Megan K. Lenox, Ian A. Brummel, Elizabeth C. Dickey, Jon F. Ihlefeld
Abstract
Abstract Biaxial stress is identified to play an important role in the polar orthorhombic phase stability in hafnium oxide‐based ferroelectric thin films. However, the stress state during various stages of wake‐up has not yet been quantified. In this work, the stress evolution with field cycling in hafnium zirconium oxide capacitors is evaluated. The remanent polarization of a 20 nm thick hafnium zirconium oxide thin film increases from 9.80 to 15.0 µC cm −2 following 10 6 field cycles. This increase in remanent polarization is accompanied by a decrease in relative permittivity that indicates that a phase transformation has occurred. The presence of a phase transformation is supported by nano‐Fourier transform infrared spectroscopy measurements and scanning transmission electron microscopy that show an increase in ferroelectric phase content following wake‐up. The stress of individual devices field cycled between pristine and 10 6 cycles is quantified using the sin 2 ( ψ ) technique, and the biaxial stress is observed to decrease from 4.3 ± 0.2 to 3.2 ± 0.3 GPa. The decrease in stress is attributed, in part, to a phase transformation from the antipolar Pbca phase to the ferroelectric Pca 2 1 phase. This work provides new insight into the mechanisms controlling and/or accompanying polarization wake‐up in hafnium oxide‐based ferroelectrics.