Oxide Membranes from Bulk Micro-Machining of SrTiO₃ Substrates

Suspended micro-structures made of epitaxial complex oxides rely on surface micro-machining processes based on sacrificial layers. These processes prevent to physically access the microstructures from both sides, as substantial part of the substrate is not removed. In this work, a bulk micromachining protocol is developed for a commonly used substrate employed in oxide thin films deposition. Suspended oxide thin film devices are realized by fabricating pass-through holes across SrTiO₃(100) or SrTiO₃(110) substrates. Careful calibration of anisotropic etching rates allows controlling the final geometry of the aperture in the substrate in a predictable way. As demonstrators of possible device geometries, clamped membranes and trampolines realized from deposited thin films of (La,Sr)MnO₃, a conductive magnetic oxide, and a suspended trampoline resonator carved from the SrTiO₃ substrate itself are presented. Reported protocols can be readily applied to a broad variety of other complex oxides so to extend the use of membranes technology beyond those of commercially available silicon compounds.