Thermodynamic control of ferroelectric-phase formation in HfxZr1−xO2 and ZrO2.

Since ferroelectric Hf_xZr_1−xO₂ is different from other ferroelectric doped-HfO₂ materials in terms of the dopant sensitivity of the formation of a ferroelectric phase, the mechanism of formation of a ferroelectric phase is investigated in comparison with that in ZrO₂. It is found that ferroelectric Hf_xZr_1−xO₂ follows a unique phase-transition pathway from tetragonal to monoclinic phases similar to that in other doped HfO₂ materials. The phase diagram of the HfO₂–ZrO₂ solid-solution system is reconsidered thermodynamically by taking into account the effects of both film thickness and nonequilibrium fabrication conditions on structural phase stability. The formation mechanism of a ferroelectric phase in the Hf_xZr_1−xO₂ system over a wide range of Hf/Zr concentration ratios is qualitatively (but clearly) understandable from these thermodynamic considerations. Finally, it is demonstrated that both ferroelectric and antiferroelectric ZrO₂ films can be formed on the same substrate by controlling the nucleation of monoclinic and tetragonal phases, respectively. [ABSTRACT FROM AUTHOR]