Nano-fabrication dependent quality factor in photonic crystal slab biosensors

Photonic crystal slabs (PCS) are attractive for label-free optical bio-sensors inside micro-fluidic portable diagnostic systems due to their high sensitivity and easy coupling to external radiation. Obtaining high quality factor (Q) values for the guided resonances in these index-of-refraction PCS biosensors is crucial for high sensitivity. Non-ideal fabrication of the hole array in the PCS due to electron beam writing, pattern transfer, and reactive ion etching (RIE) steps will result in imperfect circular hole shapes, and non vertical hole profile that can reduce the Q values. We evaluate the effect of nano-fabrication on the quality factor of guided resonances in PCS biosensors and investigate the potential limitations on sensitivity with current fabrication technologies in a realistic PCS biosensor due to fabrication errors. Spectral broadening of the guided resonances (lower Q values) is found for the fundamental guided resonance modes but no significant changes were observed in higher order guided resonances. These fin dings are consistent with reduced bio-sensing sensitivity in higher order modes due to reduced field overlap with the analyte in side the micro-fluidic channels.