Large‐Scale Hf_0.5Zr_0.5O₂ Membranes with Robust Ferroelectricity

Abstract

Hafnia‐based compounds have considerable potential for use in nanoelectronics due to their compatibility with complementary metal–oxide–semiconductor devices and robust ferroelectricity at nanoscale sizes. However, the unexpected ferroelectricity in this class of compounds often remains elusive due to the polymorphic nature of hafnia, as well as the lack of suitable methods for the characterization of the mixed/complex phases in hafnia thin films. Herein, the preparation of centimeter‐scale, crack‐free, freestanding Hf0.5Zr0.5O2 (HZO) nanomembranes that are well suited for investigating the local crystallographic phases, orientations, and grain boundaries at both the microscopic and mesoscopic scales is reported. Atomic‐level imaging of the plan‐view crystallographic patterns shows that more than 80% of the grains are the ferroelectric orthorhombic phase, and that the mean equivalent diameter of these grains is about 12.1 nm, with values ranging from 4 to 50 nm. Moreover, the ferroelectric orthorhombic phase is stable in substrate‐free HZO membranes, indicating that strain from the substrate is not responsible for maintaining the polar phase. It is also demonstrated that HZO capacitors prepared on flexible substrates are highly uniform, stable, and robust. These freestanding membranes provide a viable platform for the exploration of HZO polymorphic films with complex structures and pave the way to flexible nanoelectronics.

Anisotropic Strain‐Mediated Symmetry Engineering and Enhancement of Ferroelectricity in Hf0.5Zr0.5O2/La0.67Sr0.33MnO3 Heterostructures

“…For the LSMO films grown on KTO(110) C and GSO(100) O substrates with relatively large a sub , by contrast, the Q x values of the film and substrate are different, signifying a partially relaxed strain state. Moreover, the differences in the Q x values for the (310) C diffractions are larger than those for the (222) C diffractions, which means that the strain relaxation along the in-plane [1][2][3][4][5][6][7][8][9][10] C axis is more significant than that along the inplane [001] C axis. The anisotropic strain state can be modulated by the cooperation between the lattice mismatch and the symmetry mismatch between the substrate and film.…”

“…Notably, the 4 LSMO{011} C spots are well aligned to 4 of the 12 HZO{-111} diffraction spots. Given a (111)-oriented single domain of O-, R-, or T-phase, the three crystallographic directions, [-111], [1][2][3][4][5][6][7][8][9][10][11], and , should correspond to 3 spots in a pole figure, located at χ≈71° and separated by a ϕ difference of ≈120°. [2] Therefore, the 12 spots imply that there are 4 kinds of structural domains.…”

“…The ferroelectricity in hafnium‐based binary oxides has attracted increasing research interest over the past decade. [ 1–6 ] Distinct from their perovskite‐structured ferroelectric (FE) counterparts, hafnium‐based binary oxides exhibit robust FE polarization at the nanometer scale and superior compatibility with complementary metal‐oxide‐semiconductor (CMOS) technology. [ 7–10 ] These advantages make hafnium‐based binary oxides promising material systems to realize ultra‐scaled FE‐based devices.…”

“…The ferroelectricity in hafnium-based binary oxides has attracted increasing research interest over the past decade. [1][2][3][4][5][6] contributes to the ferroelectricity (Table S1, Supporting Information). [19,20] The complicated competition and cooperation among these structural polymorphs, together with the variable growth orientations, make the epitaxial strain a unique tuning knob to control the ferroelectricity in epitaxial HZO films.…”

“…) and (1-10) atomic plane spacing ε A = d LSMO(001) /√2d LSMO(1)(2)(3)(4)(5)(6)(7)(8)(9)(10) . As summarized in Figure2g, depending on the substrate, the lattice anisotropy varies dramatically.…”