The transfer of ferroelectric and piezoelectric BaTiO3 epitaxial thin films from an original MgO(100) single-crystal substrate to a polyethylene terephthalate (PET) sheet has been studied to fabricate flexible epitaxial functional oxides. The outline of our previous transfer process is as follows: the epitaxial BaTiO3 thin films were deposited on the MgO(100). Then, the surface of the BaTiO3 was adhered onto a PET sheet. Finally, only the MgO(100) substrate was dissolved in a phosphoric aqueous solution, which resulted in the transfer of the epitaxial BaTiO3 thin film from the MgO(100) to a PET sheet. To establish this transfer process, our aim was to prevent any damage, such as cracks and exfoliation, during the transfer of the epitaxial functional oxides. We found that a Pt buffer layer with a ductile nature was effective for improving the quality of transferred epitaxial BaTiO3 thin films. Moreover, the epitaxial BaTiO3 thin films showed a drastic shrinkage of ca. 10%. The surfaces of the shrunk, epitaxial BaTiO3 thin films showed giant wrinkles with a micrometer-order amplitude and a 10-μm-order periodicity without any damage. The epitaxial BaTiO3 thin films with giant wrinkles, accompanied by drastic shrinkage, are similar to the thin films that are coated on a pre-stretched elastomer, which is one of the fabrication processes of stretchable devices.
Keywords: BaTiO3; flexible device; giant wrinkle; shrinkage; transfer process.