Luminescent Silicon-Rich Nitride Horizontal Air-Slot Microdisk Resonators for Biosensing

We report on the fabrication and biosensing application results of luminescent horizontal air slot microdisk resonators based on silicon-rich nitride (SRN). The SRN provides the high refractive index contrast for tight mode confinement and small device sizes, and also emits light in the 800-nm wavelength range that is compatible with both aqueous environment typical of biosensors and standard silicon photodetectors. The 8-mu m-diameter pedestal-type horizontal air-slot disk resonators with 135-nm-thick SRN disks and 25-nm thin air slots were designed for a single-mode operation in the vertical dimension and slot-mode overlap of 17.4 %, and fabricated using photolithography and selective etching. Whispering gallery mode emission with the Q-factors of 6100 is excited via top-pumping, and detected using a Si charge-coupled device detector in a side-photoluminescence setup. Using bovine albumin serum and biotin/streptavidin reaction pair, the surface sensitivity of 4.6 nm/nm and 4.79 nm/(mu g-ml) is demonstrated.