Lossy Mode Resonance and Hyperbolic Mode Resonance-Based Optical Sensors by Means of Y₃Fe₅O₁₂ and SrTiO₃ Films Deposition on Planar Substrates

This letter describes the fabrication of sensor devices based on lossy mode resonance (LMR) and hyperbolic mode resonance (HMR) using for the first time as generating materials of the optical resonances both, yttrium iron garnet (Y₃Fe₅O₁₂) and strontium titanate (SrTiO₃) with a film thickness of 739.2 and 158.7 nm for Y₃Fe₅O₁₂ (YIG) and SrTiO₃, respectively. First-order resonances were observed at the visible region of the electromagnetic spectrum for both materials, LMR and HMR phenomena. RF sputtering deposition was used to fabricate metal oxide thin films on coverslips in a planar waveguide configuration, the Au metallic thin films were deposited by pulsed dc sputtering in a magnetron system from Moorfield. All devices were characterized under different surrounding medium refractive index. Sensitivities achieved values of 5862 and 5865 nm/RIU (refractive index unit) for HMR versions of Y₃Fe₅O₁₂ and SrTiO_3r, respectively. In addition, the response of the sensors to relative humidity and different ethanol concentrations was evaluated. The best results correspond to the Y₃Fe₃O₃-based sensor, with a sensitivity of 0.2 nm/ppm and a limit of detection (LOD) of 183 ppm for ethanol, and 64 nm/%RH for RH, with an LOD of 2.23%RH,