Domain Wall Evolution in Hf _0.5 Zr _0.5 O ₂ Ferroelectrics under Field-Cycling Behavior

HfO₂-based ferroelectrics have evoked considerable interest owing to the complementary metal-oxide semiconductor compatibility and robust ferroelectricity down to a few unit cells. However, the unique wake-up effect of HfO₂-based ferroelectric films severely restricts the improvement of their performance. In particular, the domain structure is an important characteristic of ferroelectric materials, which still has not been well understood in HfO₂-based ferroelectrics. In this work, a Hf_0.5Zr_0.5O₂ ferroelectric thin film is grown on a typical Si substrate buffered with TiN electrode. The 90° domains of the <i>Pca</i>2₁ ferroelectric phase with head-to-tail and tail-to-tail structures can be observed by <i>C</i>s-corrected scanning transmission electron microscope under their pristine condition. After waking up, the 180° domain is displayed in the ferroelectric phase. The remarkable differences in domain walls for 90° and 180° domains are characterized by qualitatively mapping the polarization distributions at the atomic scale. The domain wall changes from the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>[</mml:mo> <mml:mrow><mml:mn>10</mml:mn> <mml:mover><mml:mn>1</mml:mn> <mml:mo>¯</mml:mo></mml:mover> </mml:mrow> <mml:mo>]</mml:mo></mml:math> of the Hf_0.5Zr_0.5O₂ film to the [001] of the Hf_0.5Zr_0.5O₂ film. This result provides fundamental information for understanding the domain structure of HfO₂-based ferroelectrics.