Spectral Interrogation of ZnO Thin Film for Lossy Mode Resonance Sensors

ZnO thin film is theoretically investigated to explore its sensing characteristics using Fresnel reflection coefficients. Although SPR (Surface plasmon resonance) spectrum of the ZnO film has been investigated by the scientific community at a large scale but its LMR (Lossy Mode Resonance) spectrum is yet to be investigated in depth. Spectral interrogations of ZnO thin film placed on the glass prism are carried out for the generation of LMRs. The results are presented for TE as well as TM polarizations. The effect of a matching layer, inserted between substrate (prism) and ZnO thin film is also discussed in detail. A substantial improvement in the sensitivity is observed after introducing the optimized matching layer. FWHM (Full width at half maximum) of the various sensor configurations is calculated and it is inferred that a high index matching layer gives higher sensitivity. On the other hand, a low index matching layer results in higher resolution. It is shown that a high sensitivity value of 5220 nm/RIU can be achieved for TM polarization. The proposed sensor configurations with clad index range (1.44-1.48) may find applications to sense various petroleum products.