Ferroelectricity in and antiferroelectricity in nanolaminates and superlattices based on fluorite-structure oxides for future memory and energy applications
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박민혁 부산대학교 The emergence of ferroelectric properties of HfO2 and ZrO2 nanolaminates and superlattices grown through atomic layer deposition (ALD) on a TiN electrode, and the physical mechanisms behind them, are comprehensively examined. The polymorphism and resulting ferroelectric properties are strongly affected by the starting layer material (either HfO2 or ZrO2), the thickness ratio between the HfO2 and ZrO2 layers, and the single-layer thickness. ZrO2-starting samples become better crystallized during the ALD process, and a more monoclinic phase is formed during crystallization annealing. This can be understood based on the volume increase during the martensitic phase transformation from the orthorhombic/ tetragonal to the monoclinic phase, which occurs during the annealing or cooling. The effect of the thickness ratio between the HfO2 and ZrO2 layers are similar to the Hf:Zr cationic ratio in solid-solution films in the previous studies. The influence of single-layer thickness on the ferroelectric performance is strongly related to the presence of interfacial non-ferroelectric layers between the HfO2 and ZrO2 layers. Moreover, this study can shed new light on the understanding of the origin of the formation of the unexpected ferroelectric phase in fluorite oxide thin films.[1] [1] M. H. Park et al. Appl. Phys. Rev. 6, 041403 (2019). |