Investigating the Electromechanical Behavior of Unconventionally Ferroelectric $Hf_{0.5}Zr_{0.5}O_{2}$-based Capacitors Through Operando Nanobeam X-ray Diffraction

TL;DR

This study investigates the weak and unconventional electromechanical response of hafnia-based ferroelectric capacitors using operando nanobeam X-ray diffraction, revealing negative piezoelectric effects and voltage-dependent behaviors.

Contribution

It provides new insights into the negative piezoresponse and voltage suppression phenomena in hafnia-based ferroelectric capacitors through combined experimental and first-principles analysis.

Findings

Pristine rhombohedral phase exhibits negative piezoelectric coefficient (~ -0.5 to -0.8 pm/V).

Piezoelectric response is suppressed above coercive voltage.

Unconventional polarization switching behavior differs from normal ferroelectrics.

Abstract

Understanding various aspects of ferroelectricity in hafnia-based nanomaterials is of vital importance for the development of future non-volatile memory and logic devices. Here, the unconventional and weak electromechanical response of epitaxial $La_{0.67}Sr_{0.33}MnO_{3}$/$Hf_{0.5}Zr_{0.5}O_{2}$/$La_{0.67}Sr_{0.33}MnO_{3}$ ferroelectric capacitors is investigated, via the sensitivity offered by nanobeam X-ray diffraction experiments during application of electrical bias. It is shown that the pristine rhombohedral phase exhibits a negative linear piezoelectric effect with piezoelectric coefficient ($d_{33}$) ~ -0.5 to -0.8 pm$V^{-1}$. First-principles calculations support an intrinsic negative piezoresponse. In addition, it is found that the piezoelectric response is suppressed above the coercive voltage. For higher voltages, and with the onset of DC conductivity throughout the capacitor, a second-order effect is observed. The electromechanical response observed in this work is clearly different from that of normal ferroelectrics, again underlining the unconventional nature of polarization switching in the samples.