Single-Crystalline Rutile Oxide Nanomembranes: Versatile Platform to Overcome Lattice Mismatch

The demand for high-performance electronics and photonics calls for the integration of heteroepitaxial oxide films with perfect crystallinity to fully exploit emerging phenomena (e.g., metal-insulator transition, high-electron mobility) from the ionic crystals. However, the requirement of the lattice matching between epilayer and dissimilar substrates drastically limits high-quality epitaxial growth, which in turn degrades the unique properties from functional oxides; this fundamental obstacle of the heteroepitaxy prevents the unrestricted integration of the single-crystalline oxide films onto any desired substrates.<br/>To overcome this fundamental limitation, here, I present our research group efforts to demonstrate the heterogeneous integration of single-crystalline rutile oxide nanomembranes with steep phase transition onto arbitrary substrates. First, we discovers new combination of sacrificial layer and mild etchant by exploiting selective oxidation and transformation to layered structure, which could be exfoliated and dispersed in the solution to release millimeter-scale TiO₂ nanomembrane with any deterioration of crystal quality. Interestingly, nearly perfect single-crystallinity of transferred TiO₂ nanomembrane as a template for epitaxy permits the heterogeneous integration of single-crystal VO₂ films on silicon; indeed surprising sharp transition and the highest modulation of resistivity ratio ever reported was remarkably achieved even in the ultrathin VO₂ films on silicon, which is not achievable via direct growth [1]. Moreover, I will also present our epitaxial oxide nanomembrane as an versatile platform for steep phase transition even above critical thickness for lattice mismatch using the concept of pseudo-compliant substrates and emerging devices using single-crystalline oxide heterostructure (e.g., VO₂/PMN-PT heterostructure) [2]. Our finding will create new paradigm for the unrestricted application of emerging phenomena in oxide heterostructures on main-stream microelectronics.<br/><br/>This work was performed in collaboration with Dr. Dong Kyu Lee, Dr. Yunkyu Park, Sung Won Lee, Hyeji Sim, Dr. Younghak Kim, Dr. Gi-Yeop Kim and Prof. Si-Young Choi.<br/><br/>[1] D. K. Lee <i>et al.</i>, <i>Nature Commun.</i> <b>12</b>, 5019 (2021)<br/>[2] D. K. Lee <i>et al.</i>, (unpublished)