Nucleation-Limited Ferroelectric Orthorhombic Phase Formation in Hf0.5Zr0.5O2 Thin Films

Various possibilities have been proposed as the cause of the doped- or undoped-HfO2 thin film materials showing unusual ferroelectricity. These assumptions are based on empirical results, yet finding the origin of the unprecedented ferroelectricity within HfO2 has suffered from a serious gap between its theoretical calculation, mostly based on thermodynamic approach and the actual experimental results. To fill the gap, this study proposes to consider the kinetic energy, providing the evidence of the kinetic energy barrier upon a phase transformation from the tetragonal phase to the monoclinic phase affected by the TiN top electrode (capping layer). 10 nm thick Hf0.5Zr0.5O2 thin films are deposited and annealed with or without the TiN capping layer with subsequent annealing at different time and temperature. Arrhenius plot is constructed to obtain the activation energy for the tetragonal-to-monoclinic phase transformation by calculating the amount of the transformed phase using X-ray diffraction pattern. Johnson-Mehl-Avrami and nucleation-limited transformation models are utilized to describe the characteristic nucleation and growth time and calculate the activation energy for the monoclinic phase transformation of the Hf0.5Zr0.5O2 thin film. Both models demonstrate that the TiN capping layer provides a kinetic energy barrier for tetragonal-to-monoclinic phase transformation and enhances the ferroelectric property.