Identification of the different phase structures in hafnium oxide ferroelectric thin films by atomic image simulations

Hafnium oxide ferroelectric memory offers non-volatility, low power consumption, fast read-write speed, <1 ​nm scalability, and CMOS compatibility, making it a promising next-generation nonvolatile memory device. However, because the ferroelectric phase is not thermodynamically stable, hafnium oxide thin film prepared by atomic layer deposition contains several phases with very similar structures. For example, the orthorhombic and tetragonal phases are nearly indistinguishable when the grain size is small using synchrotron radiation X-ray diffraction, challenging its characterization and mechanism study. In this work, the multi-slice algorithm was utilized to simulate atomic scanning transmission electron microscopy images. For the experimental part, aberration-corrected scanning transmission electron microscopy was employed to acquire high-angle annular dark-field images and annular bright-field images. Based on the results, we proposed that when utilizing specific orientation to distinguish various phases, imaging conditions such as spherical aberration coefficient, tilt angle, film thickness, etc., affect the analysis to some extent. This work lays the foundation for understanding hafnium-based ferroelectric phase structure.