Fabrication and transfer of ultra-thin YBa$2$Cu$3$O$_{7-x}$ film on SrTiO$_3$ nanomembrane

Abstract

The fabrication of free-standing ultra-thin films from high-temperature (high-Tc) superconductors is of great interest for the development of superconducting nanowire single-photon detectors with high operating temperatures. We successfully fabricate a millimeter-sized, high-quality, ultra-thin YBa$2$Cu$3$O$_{7-x}$ (YBCO) film on an SrTiO$_3$/Sr$_{1.5}$Ca$_{1.5}$Al$_2$O$_6$ (STO/SCAO) bilayer using high-pressure sputtering. The STO nanomembranes with the YBCO films are released by dissolving the water-soluble SCAO sacrificial layer and transferred onto the SiO2/Si substrate. X-ray diffraction confirms that STO and YBCO crystallinity is preserved following transfer onto SiO2/Si substrates. Microbridges patterned from the transferred YBCO films exhibit a critical temperature of 88.8 K and a critical current density of 6.8 MA/cm2 at 77 K, demonstrating robust superconducting transport after transfer. The thermal boundary conductance across the van der Waals interface between the STO nanomembrane with YBCO film and the SiO2/Si substrate, measured over 15-75 K, is significantly reduced compared to that of epitaxial YBCO film on bulk STO leading to modified energy relaxation and enhanced stability of transient resistive states. These results establish ultra-thin YBCO films on optically transparent STO nanomembranes as a platform for integrating high-Tc superconducting devices with SiO2/Si-based photonic structures.