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

Abstract

Since ferroelectric HfxZr1−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 HfxZr1−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 HfxZr1−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.