Direct Imaging of\nAsymmetric Interfaces and Electrostatic\nPotentials inside a Hafnia–Zirconia Ferroelectric Nanocapacitor

In hafnia-based thin-film ferroelectric devices, chemical\nphenomena\nduring growth and processing, such as oxygen vacancy formation and\ninterfacial reactions, appear to strongly affect device performance.\nHowever, the correlation between the structure, chemistry, and electrical\npotentials at the nanoscale in these devices is not fully known, making\nit difficult to understand their influence on device properties. Here,\nwe directly image the composition and electrostatic potential with\nnanometer resolution in the cross section of a nanocrystalline W/Hf<sub>0.5</sub>Zr<sub>0.5</sub>O<sub>2−δ</sub> (HZO)/W ferroelectric\ncapacitor using multimodal electron microscopy. This reveals a 1.4\nnm wide tungsten suboxide interfacial layer formed at the bottom interface\nduring fabrication, which introduces a potential dip and leads to\nasymmetric switching fields. Additionally, we compare the measured\npotentials to DFT calculations and find it is nearly 3 V lower than\nexpected in the HZO, which appears to be caused by oxygen vacancies\nand a resulting negative built-in potential. These chemical and electrostatic\ndetails are important to characterize and tune to achieve high-performance\nferroelectric devices.