Abstract
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.
Highlights
The development of thin film transistors, consisting of oxide semiconductors on flexible substrates, has extended the field of oxide electronics to flexible devices [1]
We considered that the transferred epitaxial thin films were damaged by the tensile strain due to the difference between the thermal expansion of both BaTiO3 and polyethylene terephthalate (PET), which were bonded with thermal release tape
We found that introducing a Pt buffer layer is effective for improving transfer of an epitaxial BaTiO3 thin film to a PET sheet, which resulted in the successful transfer of a 10 mm × 10 mm epitaxial BaTiO3 thin film without any serious damage
Summary
The development of thin film transistors, consisting of oxide semiconductors on flexible substrates, has extended the field of oxide electronics to flexible devices [1] This first step of flexible oxide engineering uses an amorphous oxide grown at room temperature [2,3,4,5] because crystalline oxides, multi-element systems, require higher process temperatures (generally more than 500 ◦C). For bilayer systems, advanced studies in this field have developed devices using the interaction between the functionalities of the two layers beyond the het- erointerfaces [7,8,9,10,11,12] These studies have required the crystallization of oxides with appropriate structures, because these characteristic properties are accompanied by specific crystal structures. This means that the application of amorphous oxides to flexible oxide engineering is not a subject in the field of traditional oxide electronics, but it is an emerging new subject
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