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The demonstration of significant ferroelectricity in epitaxial Y-doped HfO 2 film

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ABSTRACT

Ferroelectricity and Curie temperature are demonstrated for epitaxial Y-doped HfO2 film grown on (110) yttrium oxide-stabilized zirconium oxide (YSZ) single crystal using Sn-doped In2O3 (ITO) as bottom electrodes. The XRD measurements for epitaxial film enabled us to investigate its detailed crystal structure including orientations of the film. The ferroelectricity was confirmed by electric displacement filed – electric filed hysteresis measurement, which revealed saturated polarization of 16 μC/cm2. Estimated spontaneous polarization based on the obtained saturation polarization and the crystal structure analysis was 45 μC/cm2. This value is the first experimental estimations of the spontaneous polarization and is in good agreement with the theoretical value from first principle calculation. Curie temperature was also estimated to be about 450 °C. This study strongly suggests that the HfO2-based materials are promising for various ferroelectric applications because of their comparable ferroelectric properties including polarization and Curie temperature to conventional ferroelectric materials together with the reported excellent scalability in thickness and compatibility with practical manufacturing processes.

No MeSH data available.


Schematic crystal structures of (a) YSZ (cubic fluorite), (b) ITO (bixbyite), and orthorhombic phase of YHO with (c) upward and (d) downward spontaneous polarization52. For ease of comparison, only one-eighth of the ITO unit cell is depicted. The open, dashed circles indicate unoccupied oxygen sites.
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f1: Schematic crystal structures of (a) YSZ (cubic fluorite), (b) ITO (bixbyite), and orthorhombic phase of YHO with (c) upward and (d) downward spontaneous polarization52. For ease of comparison, only one-eighth of the ITO unit cell is depicted. The open, dashed circles indicate unoccupied oxygen sites.

Mentions: To obtain material’s ferroelectric properties, a metal–ferroelectric–metal capacitor heterostructure is needed. The bottom electrode is essential because it acts as a bottom electrode for electrical measurements and as a substrate for epitaxial growth. Thus, the bottom electrode must have similar lattice parameters and, desirably, crystal structure with YSZ (see Fig. 1(a)) and also YHO-7 (Fig. 1(c,d)) together with good conductivity. We tried to insert the conductive ITO layers between YHO-7 and YSZ single crystal having fluorite structure. ITO has a bixbyite structure as illustrated in Fig. 1(b) and is often used as an oxide electrode because of its good conductivity and excellent optical transparency. Here, we focus on the crystal structure of ITO, the bixbyite structure. The bixbyite structure is a deficient fluorite structure, so we expect its lattice parameters and atomic configuration to be similar to those of YSZ and HfO2. In reality, ITO has slightly smaller lattice parameters than both the YSZ substrate and the HfO2-based dielectric layer, but it remains a feasible material for the bottom electrode. However, the previous study on the epitaxial growth on (100)ITO/(100)YSZ shows that the epitaxial YHO-7 film on the substrate tend to orient non-polar longer a-axis40. To obtain the polarization along out-of-plane component, we attempt to grow YHO-7 film on (110) ITO/(110)YSZ substrate in the present study.


The demonstration of significant ferroelectricity in epitaxial Y-doped HfO 2 film
Schematic crystal structures of (a) YSZ (cubic fluorite), (b) ITO (bixbyite), and orthorhombic phase of YHO with (c) upward and (d) downward spontaneous polarization52. For ease of comparison, only one-eighth of the ITO unit cell is depicted. The open, dashed circles indicate unoccupied oxygen sites.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5016896&req=5

f1: Schematic crystal structures of (a) YSZ (cubic fluorite), (b) ITO (bixbyite), and orthorhombic phase of YHO with (c) upward and (d) downward spontaneous polarization52. For ease of comparison, only one-eighth of the ITO unit cell is depicted. The open, dashed circles indicate unoccupied oxygen sites.
Mentions: To obtain material’s ferroelectric properties, a metal–ferroelectric–metal capacitor heterostructure is needed. The bottom electrode is essential because it acts as a bottom electrode for electrical measurements and as a substrate for epitaxial growth. Thus, the bottom electrode must have similar lattice parameters and, desirably, crystal structure with YSZ (see Fig. 1(a)) and also YHO-7 (Fig. 1(c,d)) together with good conductivity. We tried to insert the conductive ITO layers between YHO-7 and YSZ single crystal having fluorite structure. ITO has a bixbyite structure as illustrated in Fig. 1(b) and is often used as an oxide electrode because of its good conductivity and excellent optical transparency. Here, we focus on the crystal structure of ITO, the bixbyite structure. The bixbyite structure is a deficient fluorite structure, so we expect its lattice parameters and atomic configuration to be similar to those of YSZ and HfO2. In reality, ITO has slightly smaller lattice parameters than both the YSZ substrate and the HfO2-based dielectric layer, but it remains a feasible material for the bottom electrode. However, the previous study on the epitaxial growth on (100)ITO/(100)YSZ shows that the epitaxial YHO-7 film on the substrate tend to orient non-polar longer a-axis40. To obtain the polarization along out-of-plane component, we attempt to grow YHO-7 film on (110) ITO/(110)YSZ substrate in the present study.

View Article: PubMed Central - PubMed

ABSTRACT

Ferroelectricity and Curie temperature are demonstrated for epitaxial Y-doped HfO2 film grown on (110) yttrium oxide-stabilized zirconium oxide (YSZ) single crystal using Sn-doped In2O3 (ITO) as bottom electrodes. The XRD measurements for epitaxial film enabled us to investigate its detailed crystal structure including orientations of the film. The ferroelectricity was confirmed by electric displacement filed – electric filed hysteresis measurement, which revealed saturated polarization of 16 μC/cm2. Estimated spontaneous polarization based on the obtained saturation polarization and the crystal structure analysis was 45 μC/cm2. This value is the first experimental estimations of the spontaneous polarization and is in good agreement with the theoretical value from first principle calculation. Curie temperature was also estimated to be about 450 °C. This study strongly suggests that the HfO2-based materials are promising for various ferroelectric applications because of their comparable ferroelectric properties including polarization and Curie temperature to conventional ferroelectric materials together with the reported excellent scalability in thickness and compatibility with practical manufacturing processes.

No MeSH data available.