A simulation model considering sidewall deposition for the precise prediction of the performance of label-free photonic-crystal biosensors.

: Photonic-crystal (PC) structures are used as biosensors that detect the changes in the surrounding refractive index due to biomolecular interactions. In this study, a method of modeling a PC structure that considers the sidewall deposition effect during high-index layer deposition was proposed to precisely predict the performance of a label-free PC biosensor. A PC composed of nanoreplicated grating and a TiO2 high-index layer was fabricated. To replicate nanograting, a silicon mold with a 450 nm pitch and a 100 nm grating height was fabricated via photolithography and reactive ion etching. A mold cavity was coated with a self-assembled monolayer, and UV replication was performed. To realize the PC structure, a TiO2 high-index layer was deposited using the E-beam evaporation system. To design the simulation model considering the sidewall deposition effect, the cross-sectional surface profile of each PC layer was measured. Finally, the changes in the transmission spectrum of the fabricated PC structure with different buffer solutions were measured and compared with the simulated results obtained from rigorous coupled wave analysis to examine the prediction accuracy of the proposed simulation model.