Grain Size Reduction of Ferroelectric HZO Enabled by Solid Phase Epitaxy (SPE): Working Principle, Experimental Demonstration, and Theoretical Understanding
Dong Zhang, Jixuan Wu, Qiwen Kong, Zijie Zheng, Zuopu Zhou, Long Liu, Kaizhen Han, Chen Sun, Xiaolin Wang, Gan Liu, Leming Jiao, Yuye Kang, Gerui Zheng, Jiezhi Chen, Xiao Gong
Abstract
In this work, we introduce an effective and versatile technique employing replacement electrode solid phase epitaxy (SPE) to realize grain size reduction of the Zr-doped HfO2 (HZO) ferroelectric layer. This technique achieves a significant reduction in the grain size of the HZO layer by approximately 30% and simultaneously enhances the remnant polarization ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> ) by 42% compared to the conventional atomic layer deposition (ALD) growth technique. As a result, a relatively high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> value of approximately <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$25 \mu \text{C}$ </tex-math></inline-formula> /cm2 was achieved with a low thermal budget of 400 °C. In addition, we propose the underlying mechanism behind the grain size-dependent ferroelectric properties, guided by thermodynamics-included first principle simulations for the nucleation process and kinetics effects included analysis for phase change. It is discovered that the reduction in grain size plays a key role in decreasing the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${m}$ </tex-math></inline-formula> -phase and enhancing the oxygen vacancy effect, which leads to a significant improvement in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P} _{r}$ </tex-math></inline-formula> .