Freestanding Oxide Membranes for Epitaxial Ferroelectric Heterojunctions

Abstract

Since facile routes to fabricate freestanding oxide membranes were previously established, tremendous efforts have been made to further improve their crystallinity, and fascinating physical properties have been also reported in heterointegrated freestanding membranes. Here, we demonstrate our synthetic recipe to manufacture highly crystalline perovskite SrRuO 3 freestanding membranes using new infinite-layer perovskite SrCuO 2 sacrificial layers. To accomplish this, SrRuO 3 /SrCuO 2 bilayer thin films are epitaxially grown on SrTiO 3 (001) substrates, and the topmost SrRuO 3 layer is chemically exfoliated by etching the SrCuO 2 template layer. The as-exfoliated SrRuO 3 membranes are mechanically transferred to various nonoxide substrates for the subsequent BaTiO 3 film growth. Finally, freestanding heteroepitaxial junctions of ferroelectric BaTiO 3 and metallic SrRuO 3 are realized, exhibiting robust ferroelectricity. Intriguingly, the enhancement of piezoelectric responses is identified in freestanding BaTiO 3 /SrRuO 3 heterojunctions with mixed ferroelectric domain states. Our approaches will offer more opportunities to develop heteroepitaxial freestanding oxide membranes with high crystallinity and enhanced functionality.

Robust Strain in Freestanding Single-Crystal SrRuO3 Membranes

“…Silicon wafers or other various nonoxide substrates covered with freestanding SRO films can also be used as platforms for the growth of many functional oxide membranes. 24,32 It is also worth noting that efficient regulation of magnetic anisotropy, encompassing perpendicular magnetic anisotropy (PMA) as well as lateral magnetic anisotropy, holds significant importance in the development of energy-efficient and densely packed spintronic devices. junctions based on PMA have the advantages of high thermal stability, small switching current, and fast magnetization switching speed and are widely used.…”

“…It is difficult to transfer freestanding multilayer heterostructures due to the complex stress between multilayer heterostructures. Silicon wafers or other various nonoxide substrates covered with freestanding SRO films can also be used as platforms for the growth of many functional oxide membranes. , It is also worth noting that efficient regulation of magnetic anisotropy, encompassing perpendicular magnetic anisotropy (PMA) as well as lateral magnetic anisotropy, holds significant importance in the development of energy-efficient and densely packed spintronic devices. Magnetic heterojunctions based on PMA have the advantages of high thermal stability, small switching current, and fast magnetization switching speed and are widely used. , Nevertheless, the scarcity of oxide materials exhibiting PMA and the demanding conditions necessary to manipulate magnetic anisotropy have hindered their widespread implementation.…”

Vector Substrates: Idea, Design, and Realization

“…We mention in particular the demonstration of mechanical robustness of large-area membranes during transfer, [17][18][19] the repeated use of substrates on which the template layer is grown, [20] and the epitaxial growth of films on transferred membranes. [21][22][23] In this study, we integrate these advancements to develop substrates that offer distinct and important advantages over the traditional alternatives.…”

Resurrected and Tunable Conductivity and Ferromagnetism in the Secondary Growth La0.7Ca0.3MnO3 on Transferred SrTiO3 Membranes

“…Epitaxial growth of materials with diverse types of elements and structures, such as conventional semiconductors, complex oxides, organic, metals/alloys, etc., − poses significant challenges due to the highly different fabrication physics conditions required for each material. − The stackability and secondary growth of functional layers are emerged as highly promising strategies for constructing next-generation multifunctional devices; − this approach allows for the creation of complex device architectures that would otherwise be exceptionally difficult to achieve through single traditional growth methods. Moreover, secondary growth is commonly employed in device fabrication to aid in the development of integration, where a high-quality overlayer is expected to enhance the desired functionality.…”