First Principle Study on Oxygen Vacancy Induced Ferroelectricity in HFO₂-Based Ferroelectrics

HfO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> have attracted much research interest because of its wide application in beyond-moore computing based on the fantastic effects observed in the HfO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -based devices such as resistive switching and ferroelectricity. However, the physical mechanism of ferroelectricity remains elusive. Based on first principle calculations, we propose a new mechanism on the ferroelectricity in HfO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , in which the oxygen vacancies can induce ferroelectricity through symmetry-breaking mechanism. Using first principle methods, we found a stable monoclinic-like ferroelectric M <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> phase with oxygen vacancies in sub-stoichiometric Hf <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf> Zr <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-δ</inf> system and studied its ferroelectric properties. Our proposed mechanism may provide a new way for characterization and optimization of HfO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -based devices.