Crystal Phase Distribution and Ferroelectricity in Ultrathin HfO 2 –ZrO 2 Bilayers

(Hf,Zr)O 2 ultrathin films are used as ferroelectric layers in emerging digital logic and nonvolatile memory devices. The ferroelectric properties of (Hf,Zr)O 2 can be improved by interface engineering, such as the formation of nanolaminates with distinct HfO 2 and ZrO 2 layers. Herein, the ferroelectric performance of HfO 2 –ZrO 2 ultrathin bilayer devices is shown to depend on the stacking order of HfO 2 and ZrO 2 , which affects the quantity of the noncentrosymmetric orthorhombic Pca 2 1 crystal phase. By combining X‐ray diffraction with a novel extended X‐ray absorption fine structure (EXAFS) analysis procedure, the orthorhombic, tetragonal, and monoclinic phase fractions are quantified for bilayers composed of 3 nm HfO 2 and 3 nm ZrO 2 . A significantly larger orthorhombic ZrO 2 phase fraction is found when ZrO 2 has an unconstrained surface during annealing, whereas the presence of a ZrO 2 interface with the substrate results in a substantial tetragonal ZrO 2 phase fraction and a 2.4× smaller remanent polarization. HfO 2 is found to be less susceptible than ZrO 2 to crystal phase templating. The methods presented herein enable mechanistic studies of ferroelectric wake‐up, fatigue, and processing effects in (Hf,Zr)O 2 films, accelerating the development of electronic devices that rely on ferroelectric oxides.