Engineering Ferroelectric HZO With n⁺-Si/Ge Substrates Achieving High 2P_r=84 μC/cm² and Endurance >1E11

Metal-Ferroelectric-Metal (MFM) devices possessing high remanent polarizations ( $2P_{r}$ ) of 84 and $73~\mu $ C/cm2 are demonstrated with nearly epitaxially grown Hf0.5Zr0.5O2 (HZO) films on (001) n+-Si(3E19/cm $^{3}$ ) and n+-Ge(3E20/cm $^{3}$ ) substrates, respectively, which are higher than MFM devices with HZO films grown on amorphous SiO2 and partially crystallized TiN underlayers/substrates. The HZO superlattice films by sequential ZrO2/HfO2 plasma-enhanced atomic layer deposition (PEALD) process show high crystallinity in TEM images of all devices; however, the measured $2P_{r}$ values are quite different, ranging from 84 to $33\mu $ C/cm2. The high-resolution scanning transmission electron microscopy (HR-STEM) images of HZO films on n+-Si and n+-Ge show the polarization axis of o-phase is well-aligned with the growth direction which is consistent with observed high $2P_{r}$ values. Much lower interfacial energy at o-phase/Si(Ge) interfaces than m-(t-)phase/Si(Ge) by density functional theory (DFT) calculations indicates that o-phase is greatly stabilized in the HZO films on n+-Si(Ge) substrates. Strong $2P_{r}$ of 51 and $47~\mu $ C/cm2 are measured after 1E9 and 1E11 endurance cycles for HZO films on n+-Si and n+-Ge substrates, respectively. This study shows epitaxial ferroelectric HZO films could be achieved by using small misfit substrates with the thermal budget as low as 450°C.