Heteroepitaxial integration of freestanding ferroelectric BaTiO₃ on BaZrO₃ membranes

Abstract

Freestanding oxide membranes, which are free from epitaxial constraint and substrate clamping unlike complex oxide thin-film heterostructures, provide a fascinating platform for realizing multi-functional devices via heterogeneous integration of freestanding membranes with different physical properties. For further applications of freestanding membranes to actual devices, single-crystalline nanomembranes are highly essential. Herein, we demonstrate the fabrication of freestanding BaZrO₃ membranes with high crystallinity via BaZrO₃/SrCuO₂ bilayer thin films epitaxially grown on SrTiO₃ (001) substrates, followed by selective etching of the sacrificial SrCuO₂ layer. The exfoliated freestanding BaZrO₃ membranes serve as a robust template layer for the epitaxial growth of ferroelectric BaTiO₃, producing freestanding BaTiO₃/BaZrO₃ membrane heterostructures. The crystallinity and epitaxy of the as-fabricated freestanding heterojunctions is characterized by X-ray diffraction analyses. Raman spectroscopy also reveals that the upper layers of ferroelectric BaTiO₃ are mainly in-plane polarized probably due to the biaxial in-plane tensile strain imposed by the lower BaZrO₃ layer with cubic symmetry, although the initial tensile strain is progressively mitigated with the increasing thickness of the topmost BaTiO₃ layer. The perovskite BaZrO₃ membrane templates are of potential interest for designing strain-tuned heterojunctions of freestanding oxide membranes, where the associated physical properties can be manipulated compared with the bulk counterparts and/or epitaxial oxide thin-film heterostructures.

Keywords

Thin film / oxide / perovskite / freestanding membrane / heteroepitaxy

References

[1] Fernandez A.,Lee H. G..Thin-film ferroelectrics.Adv. Mater.2022;34:2108841

[2] Li T.,Liu H..Insights into strain engineering: from ferroelectrics to related functional materials and beyond.Chem. Rev.2024;124:7045-105

[3] Sando D..Strain and orientation engineering in ABO₃ perovskite oxide thin films.J. Phys. Condens. Matter.2022;34:153001

[4] Choudhary N.,Kaur D..Structural, electrical and mechanical properties of magnetron sputtered NiTi/PZT/TiO_x thin film heterostructures.Surf. Coat. Technol.2011;205:3387-96

[5] Oh Y. S.,Lee H.,Kim T. H..Polar perturbations in functional oxide heterostructures.Adv. Funct. Mater.2023;33:2302261

[6] Li Y. L.,Liu Z. K..Effect of external mechanical constraints on the phase diagram of epitaxial PbZr_1-xTi_xO₃ thin films - thermodynamic calculations and phase-field simulations.Appl. Phys. Lett.2003;83:1608-10

[7] Pan H.,Banyas E..Clamping enables enhanced electromechanical responses in antiferroelectric thin films.Nat. Mater.2024;23:944-50

[8] Griggio F.,Kumar A..Substrate clamping effects on irreversible domain wall dynamics in lead zirconate titanate thin films.Phys. Rev. Lett.2012;108:157604

[9] Shi Q.,Cheng X..The role of lattice dynamics in ferroelectric switching.Nat. Commun.2022;13:1110 PMCID:PMC8891289

[10] Ji H..On strategies for enforcing interfacial constraints and evaluating jump conditions with the extended finite element method.Int. J. Numer. Meth. Eng.2004;61:2508-35

[11] Moridi A.,Zhang L..Residual stresses in thin film systems: Effects of lattice mismatch, thermal mismatch and interface dislocations.Int. J. Solids Struct.2013;50:3562-9

[12] Zhang L.,Lapano J..Continuously tuning epitaxial strains by thermal mismatch.ACS Nano2018;12:1306-12

[13] Choo S.,Liu H.,James R. D..From oxide epitaxy to freestanding membranes: opportunities and challenges.Sci. Adv.2024;10:eadq8561 PMCID:PMC11633760

[14] Han S.,Xu Z..Freestanding membranes for unique functionality in electronics.ACS Appl. Electron. Mater.2023;5:690-704

[15] Haque M. A..Strain gradient effect in nanoscale thin films.Acta Mater.2003;51:3053-61

[16] Wang Q.,Zhang X..Emergent uniaxial magnetic anisotropy in high-integrity, uniform freestanding LaMnO₃ membranes.ACS Appl. Mater. Interfaces2024;16:68197-203 PMCID:PMC11647760

[17] Dai L.,Li J..Highly heterogeneous epitaxy of flexoelectric BaTiO_3-δ membrane on Ge.Nat. Commun.2022;13:2990 PMCID:PMC9151678

[18] Kum H.,Kong W..Epitaxial growth and layer-transfer techniques for heterogeneous integration of materials for electronic and photonic devices.Nat. Electron.2019;2:439-50

[19] Huang Z.,Wang X. R..Interface engineering and emergent phenomena in oxide heterostructures.Adv. Mater.2018;30:1802439

[20] Lee Y.,Kim H..Epitaxy of emerging materials and advanced heterostructures for microelectronics and quantum sciences.Small Methods2025;9:2401815 PMCID:PMC12391656

[21] Salles P.,Guzman R..Facile chemical route to prepare water soluble epitaxial Sr₃Al₂O₆ sacrificial layers for free‐standing oxides.Adv. Mater. Interfaces2021;8:2001643

[22] Pesquera D.,Khestanova E..Freestanding complex-oxide membranes.J. Phys. Condens. Matter2022;34:383001

[23] Sheeraz M.,Kim Y. K..Freestanding oxide membranes for epitaxial ferroelectric heterojunctions.ACS Nano2023;17:13510-21

[24] Nian L.,Wang Z..Sr₄Al₂O₇: a new sacrificial layer with high water dissolution rate for the synthesis of freestanding oxide membranes.Adv. Mater.2024;36:e2307682

[25] Bakaul S. R.,Lee M..Single crystal functional oxides on silicon.Nat. Commun.2016;7:10547 PMCID:PMC4748113

[26] Chang Y. W.,Yi J. B..A fast route towards freestanding single-crystalline oxide thin films by using YBa₂Cu₃O_7-x as a sacrificial layer.Nanoscale Res. Let.2020;15:172 PMCID:PMC7455685

[27] Takahashi R..Sacrificial water-soluble BaO layer for fabricating free-standing piezoelectric membranes.ACS Appl. Mater. Interfaces2020;12:25042-9

[28] Peng H.,Yang S..A Generic sacrificial layer for wide‐range freestanding oxides with modulated magnetic anisotropy.Adv. Funct. Mater.2022;32:2111907

[29] Kim H.,Lee S..Remote epitaxy.Nat. Rev. Methods Primers2022;2:40.

[30] Park B. I.,Lu K..Remote epitaxy: fundamentals, challenges, and opportunities.Nano Lett.2024;24:2939-52

[31] Lee J. H.,Jung M. H..Reversibly controlled ternary polar states and ferroelectric bias promoted by boosting square-tensile-strain.Adv. Mater.2022;34:e2205825

[32] Choi K. J.,Li Y. L..Enhancement of ferroelectricity in strained BaTiO₃ thin films.Science2004;306:1005-9

[33] Wang X.,Wen H..Phase transition and high dielectric constant of bulk dense nanograin barium titanate ceramics.Appl. Phys. Lett.2006;89:162902

[34] Panomsuwan G..A comparative study of dielectric and ferroelectric properties of sol-gel-derived BaTiO₃ bulk ceramics with fine and coarse grains.Appl. Phys. A2018;124:713

[35] Lin E. L.,Zheng L..Atomic layer deposition of epitaxial ferroelectric barium titanate on Si (001) for electronic and photonic applications.J. Appl. Phys.2019;126:064101

[36] Fortunato E.,Martins R..Oxide semiconductor thin-film transistors: a review of recent advances.Adv. Mater.2012;24:2945-86

[37] He F..Lattice strain in epitaxial BaTiO₃ thin films.Appl. Phys. Lett.2006;88:152908

[38] Damodaran A. R.,Chen Z.,Martin L. W..Enhancement of ferroelectric Curie temperature in BaTiO₃ films via strain-induced defect dipole alignment.Adv. Mater.2014;26:6341-7

[39] Elangovan H.,Seremi S..Giant superelastic piezoelectricity in flexible ferroelectric BaTiO₃ membranes.ACS Nano2020;14:5053-60

[40] Dong G.,Yao M..Super-elastic ferroelectric single-crystal membrane with continuous electric dipole rotation.Science2019;366:475-9

[41] Azar S. A.,Mousa A. A.,Jaradat E. K..Investigation of electronic, optical and thermoelectric properties of perovskite BaTMO₃ (TM = Zr, Hf): First principles calculations.J. Alloys Compd.2021;887:161361

[42] Vera C. Y. R.,Peterson D..A mini-review on proton conduction of BaZrO₃-based perovskite electrolytes.J. Phys. Energy2021;3:032019

[43] Kolodiazhnyi T.,Vittayakorn W..Giant suppression of dielectric loss in BaZrO₃.J. Eur. Ceram. Soc.2019;39:4144-8

[44] Harbola V.,Hong S. S..Experimental progress in freestanding oxide membranes designed by epitaxy.Adv. Phys. X.2025;10:2450538

[45] Duong N. X.,Jeon J..Polymorphic phase transition in BaTiO₃ by Ni doping.Ceram. Int.2019;45:16305-10

[46] Xu C.,Hong P.,Yang Z..Lignin/graphene oxide composite coating loaded with zinc ions and its photothermal conversion and self-healing anticorrosion properties.Microstructures2025;5:2025037

[47] Xu R.,Barnard E. S..Strain-induced room-temperature ferroelectricity in SrTiO₃ membranes.Nat. Commun.2020;11:3141 PMCID:PMC7305178

[48] Huang S.,Ma C..Ferroelectric order evolution in freestanding PbTiO₃ films monitored by optical second harmonic generation.Adv. Sci.2024;11:e2307571 PMCID:PMC11348163

[49] Zhou M.,Tan Y.,Chen L..Domain evolution, dielectric and piezoelectric response in bent freestanding PbTiO₃ ferroelectric nanowires.Acta Mater.2025;288:120805

[50] Pesquera D.,Qualls A..Beyond substrates: strain engineering of ferroelectric membranes.Adv. Mater.2020;32:e2003780

[51] Degezelle A.,Gemeiner P..Strain‐induced polarization rotation in freestanding ferroelectric oxide membranes.Adv Electron Mater2025;11:e00266

[52] Didomenico M.,Porto S. P. S..Raman spectrum of single-domain BaTiO₃.Phys Rev1968;174:522-30

[53] Marssi M. E.,Lukyanchuk I. A..Ferroelectric transition in an epitaxial barium titanate thin film: Raman spectroscopy and x-ray diffraction study.J. Appl. Phys.2003;94:3307-12

[54] Silva J. P. B.,Almeida A.,Pereira M..Influence of laser repetition rate on ferroelectric properties of pulsed laser deposited BaTiO₃ films on platinized silicon substrate.Appl. Phys. A2013;113:379-84