Robust SiON rib waveguides for CMOS-compatible surface plasmon resonance sensing of aqueous analytes

Silicon oxynitride (SiON) is a highly adaptable material platform for photonic integrated circuits owing to its refractive index tunability and full CMOS compatibility. In this work, an integrated surface plasmon resonance (SPR) sensor based on a robust SiON rib waveguide is demonstrated. The sensor geometry and modal properties were optimized using two-dimensional finite element method (FEM) simulations. The sensor performance was evaluated by direct edge coupling within the 550–915 nm spectral range. The influence of the plasmonic layer was first investigated by tracking the resonance dip for gold thicknesses of 20–40 nm with dimethyl sulfoxide (DMSO, n = 1.47) as the analyte. The response was then simulated matching approximately volumetric water-isopropyl alcohol (IPA) mixtures ( n = 1.33–1.38), yielding an averaged sensitivity of 158 nm/RIU changing from 80 (water) up to 350 (IPA) nm/RIU that increases with the analyte refractive index. The results confirm that matching the SiON core refractive index to the target analyte enhances the evanescent coupling and thereby the sensitivity. The combination of index tunability, robust architecture, and simple CMOS-compatible fabrication makes the presented platform a versatile candidate for lab-on-a-chip sensing.