Super-tetragonal Sr4Al2O7: a versatile sacrificial layer for high-integrity freestanding oxide membranes

TL;DR

This paper introduces super-tetragonal Sr4Al2O7 as a water-soluble sacrificial layer that enables the fabrication of large, crack-free, freestanding oxide membranes with high structural integrity, advancing oxide electronics and flexible device applications.

Contribution

It demonstrates the use of super-tetragonal Sr4Al2O7 as a novel, versatile sacrificial layer for high-quality, large-area freestanding oxide membranes with minimal cracks and high strain tolerance.

Findings

Crack-free oxide membranes up to millimeter scale.

High water solubility of Sr4Al2O7 facilitates membrane release.

Structural coherency reduces defect formation.

Abstract

Releasing the epitaxial oxide heterostructures from substrate constraints leads to the emergence of various correlated electronic phases and paves the way for integrations with advanced semiconductor technologies. Identifying a suitable water-soluble sacrificial layer, compatible with the high-quality epitaxial growth of oxide heterostructures, is currently the key to the development of large-scale freestanding oxide membranes. In this study, we unveil the super-tetragonal Sr4Al2O7 (SAOT) as a promising water-soluble sacrificial layer. The distinct low-symmetric crystal structure of SAOT enables a superior capability to sustain epitaxial strain, thus allowing for broad tunability in lattice constants. The resultant structural coherency and defect-free interface in perovskite ABO3/SAOT heterostructures effectively restrain crack formations during the water-assisted release of freestanding oxide membranes. For a variety of non-ferroelectric oxide membranes, the crack-free areas can span up to a few millimeters in length scale. These compelling features, combined with the inherent high-water solubility, make SAOT a versatile and feasible sacrificial layer for producing high-quality freestanding oxide membranes, thereby boosting their potential for innovative oxide electronics and flexible device designs.