Identification of Structural Phases in Al Doped HfO₂-based Ferroelectric Films by DFT-Assisted EXAFS Analysis

Abstract

$HfO_2$-based ferroelectrics have become important for future applications in CMOS technology such as negative capacitance low-power field effect transistor (FET) logic, FeRAM or FeFET memory, and FeFET- or ferroelectric tunnel junction (FTJ)-based neural network accelerators. In our previous studies, we have used density-functional theory (DFT)-assisted extended X-ray absorption fine-structure spectroscopy (EXAFS) to identify the crystalline phases in the films of ($Hf_{0.46}Zr_{0.54}O_2$) as grown by atomic layer deposition [1]. In these films, Ferroelectric switching in TiN/$Hf_{0.46}Zr_{0.54}O_2$/TiN metal-insulator-metal capacitors is verified. We confirmed that the frequently invoked polar orthorhombic $ Pca2_1 $ phase is present in ferroelectric hafnium zirconium oxide, along with an equal amount of the non-polar monoclinic $ P2_1/c $ phase. For comparison, we verified that paraelectric $ HfO_2$ films exhibit the $ P2_1/c $ phase. In this study we are extending our studies to identify the crystalline phases in Al-doped $ HfO_2 $ thin films. We have again used density functional theory (DFT)-assisted extended X-ray absorption fine-structure spectroscopy (EXAFS) to determine the structural symmetry of Al doped $ HfO_2 $ thin films. The 8-nm thick $ HfO_2 $-based films were grown by atomic layer deposition in a metal-insulator-metal (MIM) stack configuration with varying doping levels Al and annealing temperatures. Grazing-incidence fluorescence-yield mode $ Hf L_3 $ and Zr K absorption edge EXAFS experiments were performed at the 6-BM beamline at the National Synchrotron Light Source II of Brookhaven National Laboratory. The results of the EXAFS multiphase fitting and the effect of Al doping levels to crystalline phases will be discussed in conjunction with the electrical properties [1] M.A. Sahiner et al., Appl. Phys. Lett. 118, 092903 (2021)