Enhanced Switching Reliability of Hf_0.5Zr_0.5O₂ Ferroelectric Films Induced by Interface Engineering

Area of Science:

• Materials Science
• Solid-State Physics
• Nanotechnology

Background:

• Hafnia-based ferroelectric thin films, such as hafnium zirconium oxide (HZO), are promising for scaled semiconductor memories due to CMOS compatibility.
• Polarization instability, specifically the 'wake-up' effect, hinders the technological implementation of these materials.
• Understanding the mechanisms behind polarization variation during field cycling is crucial for device improvement.

Purpose of the Study:

• To investigate methods for mitigating the polarization wake-up effect in ferroelectric Hf_0.5Zr_0.5O₂ (HZO) capacitors.
• To elucidate the role of the HZO/electrode interface in HZO ferroelectric performance and wake-up mechanisms.

Main Methods:

• Fabrication of HZO capacitors with and without ultrathin HfO₂ buffer layers at the HZO/electrode interface.
• High-resolution transmission electron microscopy (HRTEM) to analyze film microstructure and crystallite size.
• Synchrotron X-ray diffraction (XRD) to study phase transformations (tetragonal to orthorhombic) during electric field cycling.

Main Results:

• HZO capacitors with HfO₂ buffer layers exhibited significantly reduced polarization wake-up.
• HRTEM revealed larger crystallite sizes in buffer layer capacitors, indicating influenced crystallization during annealing.
• XRD confirmed the conversion of the nonpolar tetragonal (T) phase to the polar orthorhombic (O) phase in control devices, correlating with wake-up, while buffer layers promoted the O phase initially.

Conclusions:

• Ultrathin HfO₂ buffer layers effectively suppress the polarization wake-up phenomenon in HZO ferroelectric capacitors.
• The buffer layers influence HZO crystallization, promoting the formation of the desired polar phase and enhancing device stability.
• These findings offer critical insights into interface engineering for optimizing hafnia-based ferroelectrics in advanced memory technologies.