Microfabrication of SrRuO₃ thin films on various oxide substrates using LaAlO₃/BaO_x sacrificial bilayers

Oxides provide various fascinating physical properties that could find use in future device applications. However, the physical properties of oxides are often affected by formation of oxygen vacancies during device fabrication processes. In this study, to develop a damage-free patterning process for oxides, we focus on a lift-off process using a sacrificial template layer, by which we can pattern oxide thin films without severe chemical treatment or plasma bombardment. As oxides need high thin-film growth temperature, a sacrificial template needs to be made of thermally stable and easily etchable materials. To meet these requirements, we develop a sacrificial template with a carefully designed bilayer structure. Combining a thermally and chemically stable LaAlO₃ and a water-soluble BaO_x, we fabricated a LaAlO₃/BaO_x sacrificial bilayer. The patterned LaAlO₃/BaO_x sacrificial bilayers were prepared on oxide substrates by room-temperature pulsed laser deposition and standard photolithography process. The structure of the sacrificial bilayer can be maintained even in rather tough conditions needed for oxide thin film growth: several hundred degrees Celsius under high oxygen pressure. Indeed, the LaAlO₃/BaO_x bilayer is easily removable by sonication in water. We applied the lift-off method using the LaAlO₃/BaO_x sacrificial bilayer to a representative oxide conductor SrRuO₃ and fabricated micron-scale Hall-bar devices. The SrRuO₃ channels with the narrowest line width of 5 μm exhibit an almost identical transport property to that of the pristine film, evidencing that the developed process is beneficial for patterning oxides. We show that the LaAlO₃/BaO_x lift-off process is applicable to various oxide substrates: SrTiO₃, MgO, and Al₂O₃. The new versatile patterning process will expand the range of application of oxide thin films in electronic and photonic devices.