Hafnium oxide (HfO₂)–based thin films have attracted significant attention due to their unique ability to exhibit ferroelectricity even at thicknesses below 10 nm, making them highly promising for next-generation semiconductor technologies such as non-volatile memories, sensors, and actuators.

​

However, ferroelectricity in HfO₂ originates exclusively from the orthorhombic phase, which is metastable and therefore difficult to reliably form and maintain. This phase is governed by subtle variations in oxygen atomic positions, posing a major challenge for experimental characterization.

​

By leveraging advanced TEM techniques including in-situ electrical biasing TEM, 4D-STEM-ASTAR, and machine-learning-assisted EELS analysis, our research aims to elucidate oxygen-related reaction behaviors and phase evolution in HfO₂-based thin films. Through this approach, we seek to establish a fundamental understanding of ferroelectric phase stabilization in these materials.