A SiON microring resonator-based platform for biosensing at 850 nm

In this paper, we report on the design, fabrication, and characterization of a photonic circuit for biosensing applications. Silicon oxynitride with a bulk refractive index of 1.66 is the core-layer material. The photonic circuit is optimized for a wavelength of ~850 nm, which allows on-chip integration of the light source via cost effective vertical-cavity surface-emitting lasers and of the detector by using standard silicon photodetectors. Design as well as fabrication processes are explained in details. The best characteristics for the single optical components in the photonic circuit are: for single-mode channel waveguides with dimensions of 350 nm × 950 nm; propagation losses of 0.8 dB/cm; bending losses of 0.1 dB/90°-bend (radius of curvature 100 μm); 49/51 splitting ratio for 3-dB power splitters (directional couplers); quality factors up to 1.3 × 10 5 for microring resonators. Volumetric sensing yields a bulk sensitivity of 80 nm/RIU and a limit of detection of 3 × 10 -6 RIU. Therefore, SiON-based photonic circuits represent a reliable material platform for biosensing in the short-wave near infrared region.