Robust ferroelectricity in epitaxial Hf1/2Zr1/2O2 thin films

Abstract

Ferroelectric orthorhombic Hf0.5Zr0.5O2 (HZO) thin films have been stabilized epitaxially on La2/3Sr1/3MnO3/SrTiO3(001) by pulsed laser deposition. The epitaxial orthorhombic films, (111)-oriented and with very flat surface, show robust ferroelectric properties at room temperature. They present a remnant polarization around 20 μC/cm 2 without need of a wake-up process, a large coercive electric field of around 3 MV/cm, an extremely long retention extending well beyond 10 years, and an endurance up to about 10 8 cycles. Such outstanding properties in the nascent research on epitaxial HfO2based ferroelectric films, can pave the way to a better understanding of the effects of orientation, interfaces, strain and defects on ferroelectricity in HfO2.

Engineering Ferroelectric Hf0.5Zr0.5O2 Thin Films by Epitaxial Stress

“…Additional information on growth conditions of HZO and LSMO is reported elsewhere. [18][19] Structural characterization: The crystal structure (crystal phases of HZO and lattice parameters of LSMO and HZO) was characterized by X-ray diffraction using Cu Kα radiation.…”

“…10 The resulting films are polycrystalline and contain paraelectric tetragonal and monoclinic phases besides the ferroelectric orthorhombic phase. 1,2,[11][12] The ferroelectric phase has been also grown epitaxially on a few substrates, including yttria-stabilized zirconia, [13][14][15][16] LaAlO3, 17 SrTiO3, [18][19][20][21] and buffered Si. 22 The research on epitaxial stabilization is just emerging in comparison with that on polycrystalline doped HfO2 films.…”

Enhanced ferroelectricity in epitaxial Hf0.5Zr0.5O2 thin films integrated with Si(001) using SrTiO3 templates

“…S2, a XRD scan acquired with longer time and the simulation of the Laue fringes). The out-of-plane interplanar spacing, do-HZO(111) = 2.940 Å, issmaller to that of equivalent HZO films on LSMO/STO(001) (d = 2.963 Å) 17. The smaller interplanar spacing can be caused by a combined effect of differences in the strain of the LSMO electrodes and in the thermal expansion mismatches between the oxide layers and the Si and STO substrate.…”

“…In similar epitaxial HZO films deposited on STO(001) single crystalline substrates retention was also long, but only for large poling fields. 17 In contrast, the retention of Pt/HZO/LSMO capacitor on STO/Si(001) is very high after applying a 4V pulse. To estimate the polarization after longer times, the experimental data are fitted to the power-law decay usually observed 32,33 in ferroelectric oxide films (red dashed curves in Fig.…”

Magneto-ionic control of spin polarization in multiferroic tunnel junctions

“…Epitaxial growth of crystalline HZO can also be achieved [23] and has been recently also demonstrated on perovskite substrates with La 0.7 Sr 0.3 MnO 3 (LSMO) as bottom elecrode [24][25][26]. Four resistance states have been obtained in this type of junctions by both magnetic and electric field switching, but no ME coupling was reported.…”