Highly sensitive silicon nitride biomedical sensor using plasmonic grating and ZnO layer

A biomedical sensor that sense concentration of glycerol in a deionized water with a high sensitivity is introduced in this work. A silicon nitride layer is added to the grated substrate, glass, then a plasmonic layer has been used before adding a zinc oxide layer on the top of the plasmonic gratings. The dimensions of all layers have been optimized to obtain the maximum refractive index sensitivity. Finite difference time domain method is used to calculate a transmitted signal from the proposed structure with and without analyte material. Figure of merit, quality factor and full width half maximum are also calculated at different duty cycle. The best performance of the senor has been obtained at duty cycle 35%, figure of merit 57.6, quality factor 57.3 and linewidth 14 nm. The maximum refractive index sensitivity is 806 nm/RIU which calculated at the same duty cycle. Detecting the glycerol concentration in deionized water is simulated at the maximum sensitivity and measured at different incident light angle. Finally, electric and magnetic fields and optical power, distributed along the structure are illustrated and discussed. (paper)