Intrinsic ferroelectricity in Y-doped HfO2 thin films

Abstract

Ferroelectric HfO2-based materials hold great potential for widespread integration of ferroelectricity into modern electronics due to their robust ferroelectric properties at the nanoscale and compatibility with the existing Si technology. Earlier work indicated that the nanometer crystal grain size was crucial for stabilization of the ferroelectric phase of hafnia. This constraint caused high density of unavoidable structural defects of the HfO2-based ferroelectrics, obscuring the intrinsic ferroelectricity inherited from the crystal space group of bulk HfO2. Here, we demonstrate the intrinsic ferroelectricity in Y-doped HfO2 films of high crystallinity. Contrary to the common expectation, we show that in the 5% Y-doped HfO2 epitaxial thin films, high crystallinity enhances the spontaneous polarization up to a record-high 50 µC/cm2 value at room temperature. The high spontaneous polarization persists at reduced temperature, with polarization values consistent with our theoretical predictions, indicating the dominant contribution from the intrinsic ferroelectricity. The crystal structure of these films reveals the Pca21 orthorhombic phase with a small rhombohedral distortion, underlining the role of the anisotropic stress and strain. These results open a pathway to controlling the intrinsic ferroelectricity in the HfO2-based materials and optimizing their performance in applications.

Sliding ferroelectricity in van der Waals layered γ-InSe semiconductor

“…Owing to the weak interlayer vdW-force in 2D-layered materials, structural control by interlayer twist/translation has successfully enabled the realization of the unexpected interlayer sliding ferroelectricity in Moiré superlattices and TMD heterostructures with artificially-tuned broken inversion symmetry via much more complex fabrication procedures [9][10][11][12][13][14][15][16][17][18] . On the other hand, doping, especially with rare-earth elements 19 , which can change the lattice structure (such as bond distance and angle, and atom position) of materials, e.g., via microstrain/structure constrain, has also been employed as an effective strategy to tune ferroelectric properties not only in traditional perovskite-based ferroelectrics 20 but also in newlyemerging HfO 2 -based ferroelectrics 21,22 , showing great potential for manipulating the fundamental properties of 2D vdW semiconductors.…”

Ferroelectricity and negative piezoelectric coefficient in orthorhombic phase pure ZrO2 thin films

“…Recently, 10 nm thick 5% YO 1.5 -doped epitaxial HfO 2 films were grown on LSMO/STO (001) or (110) substrates with a o-structure with a small rhombohedral distortion [30]. A higher P s of about 50 µC/cm 2 and P r of about 37 µC/cm 2 was achieved for the pure o-phase films grown on LSMO/STO (110) substrates due to the high degree of structural order.…”