In this paper, the effect of dispersion on sensing parameters of a racetrack resonator-based biosensor is studied. It is shown that dispersion has a significant effect in biosensing characteristics of a resonator designed with silicon-oxy-nitride (SiON) waveguides in a racetrack configuration. Based on the results, high sensitivity (𝑆) can be achieved using a SiON racetrack resonator as a biosensing device. Simultaneously, this device has a high total quality factor (𝑄𝑡). The highest 𝑆 for a transverse electric whispering gallery mode (TE WGM) of 1 (2) is found to be 87.82 (434.94) nm/RIU at an optimized resonator radius of 69 μm (19 μm). At the same time, the highest 𝑄𝑡 factor of ∼4.6×10^4 is obtained for TE WGM 1 and 2, at biological cladding. These amounts of 𝑆 and 𝑄𝑡 factors result in an ultrahigh figure of merit (FOM) of 4766 RIU^−1 and 23705 RIU^−1, respectively, for TE WGM 1 and 2. Based on the FOM calculations, our sensor structure performs 237 orders of magnitude better than surface plasmon resonance devices for bulk refractometric sensing. Device analysis is done by simple, fast, and reliable analytical methods. The model results are validated through comparison with experimental reports.
