Grain Size Reduction of Ferroelectric HZO Enabled by Solid Phase Epitaxy (SPE): Working Principle, Experimental Demonstration, and Theoretical Understanding

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 ( ${P}_{r}$ ) by 42% compared to the conventional atomic layer deposition (ALD) growth technique. As a result, a relatively high ${P}_{r}$ value of approximately $25 \mu \text{C}$ /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 ${m}$ -phase and enhancing the oxygen vacancy effect, which leads to a significant improvement in ${P} _{r}$ .