Precise structure and polarization determination of Hf_0.5Zr_0.5O₂ with electron ptychography

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Hafnium-zirconium oxide (Hf_0.5Zr_0.5O₂) is a key material for advanced ferroelectric memories and transistors.
• The exact nature of its ferroelectricity is debated due to challenges in nanoscale characterization.

Purpose of the Study:

• To precisely characterize the nanoscale structure and ferroelectric properties of Hf_0.5Zr_0.5O₂ films.
• To investigate polarization behavior, domain walls, and oxygen vacancy distribution at ultra-high resolution.

Main Methods:

• Substrate-free Hf_0.5Zr_0.5O₂ films were analyzed using multislice electron ptychography.
• Achieved 25-picometer resolution enabling atomic imaging, depth profiling, and vacancy quantification.

Main Results:

• Ferroelectric phase polarization displacement measured at ~56 ± 6 picometers (~34 ± 4 μC/cm²).
• Significant polarization suppression observed near grain boundaries, with negligible change at neutral domain walls.
• 180° head-to-head charged domain walls confined within a unit cell were identified, showing reduced atomic displacement and high oxygen vacancy concentration.

Conclusions:

• Ultra-high resolution imaging provides critical structural data for Hf_0.5Zr_0.5O₂ ferroelectrics.
• Understanding domain wall behavior and vacancy effects is essential for optimizing ferroelectric device design.