Giant Critical Thickness in Highly Conducting Epitaxial SrMoO₃ Electrodes Investigated by Lift-Off Membranes

Within the huge perovskite materials family, thin films of highly conducting materials such as SrMoO3, SrNbO3, and SrVO3 are candidates for low-loss bottom electrodes in epitaxial all-oxide devices, in particular for high-frequency applications. Recently, the fully coherent growth of more than 5 mu m thick SrMoO3 electrodes in a varactor device prototype epitaxial heterostructure has been reported. This result raises the question of the strain mechanism in such anomalously thick coherent epitaxial layers. Here, this question is addressed by comparing the lattice constants of coherently strained layers and their free-standing membranes. SrMoO3 is mainly elastically strained within the heterostructure and fully relaxed after removal of the substrate. These results indicate a giant critical thickness, making highly conducting perovskites even more outstanding materials for high-frequency applications that require electrode thicknesses beyond the skin depth. The described technology of lifting off thick SrMoO3 membranes joins the emerging field of freestanding oxide layer technology, opening unexplored avenues for single crystal investigations, novel perovskite nanostructures, and wafer transfer of functional oxides, walking in the footsteps of recent developments in van der Waals epitaxial heterostructures.