Numerical Investigation of a High Performance Subwavelength Grating Based Plasmonic Biosensor Mahin Tahmasebpour and Manouchehr Bahrami Faculty of Electrical and Computer Engineering, University of Tabriz, Tabriz, Iran Email: {tahmasebpour, mbahrami}@tabrizu.ac.ir Asghar Asgari Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz, Iran School of Electrical, Electronic and Computer Engineering, The University of Western Australia, Crawley, WA 6009, Australia Email: asgari@tabrizu.ac.ir Abstract—A Localized Surface Plasmon Resonance (LSPR) biosensor based on a subwavelength grating structure is studied numerically for detection of bulk refractive change of aqueous environments such as biological buffer solutions. A high grating thickness of 40nm and a short grating period of 50nm are selected to evaluate numerically the effect of the other grating structural parameter i.e. fill factor (f.f) on the sensor performance including dispersion curve, sensitivity, FWHM, MRR and resonance angle. Evaluation shows that corresponding wavelength to the effective resonance of surface plasmons which locating in near infrared (NIR) wavelength range is displaced with f.f value. Also, as shown for some f.f values sensitivity is enhanced slightly whereas FWHM, MRR and resonance angle is increased. Thus with adjusting both of operating wavelength and f.f value, it is possible to get a better performance for the plasmonic sensor. Index Terms—subwavelength grating, localized surface plasmon, biosensor, near infrared wavelengths I. INTRODUCTION Surface Plasmon Resonance (SPR) is one of the most advanced label free, real time detection technologies for measurement of a refractive index change near the noble metal surfaces caused by an aqueous solution concentration or biomolecular adsorption. Useful characteristics of metallic nano-structures including local field enhancement and their metamaterial-like behavior have enhanced the sensitivity of SPR based sensors [1], [2]. In the field of LSPR sensors Kim et al. presented a nanowire-based SPR configuration in which the combination of a prism coupled method with a nano- grating coupled method enhances the sensitivity [3]. After that, this structure has been the topic of recent theoretical and experimental studies which the most focused on the sensitivity enhancement [4]-[9]. Since a narrow Full Width at Half Minimum (FWHM) and a low Manuscript received October 20, 2014; revised July 10, 2015. Minimum Reflectance at Resonance (MRR) are desired for designing a practical SPR sensor [10], [11], these performance parameters have to be enhanced as well as sensitivity. As verified in our recent work [12], overall performance of the nano-grating based SPR sensor can be improved for higher grating thicknesses and lower grating periods in NIR wavelengths. Based on the results of that work, a high grating thickness of 40 nm and a short grating period of 50 nm are selected to evaluate the effect of the other grating structural parameter i.e. fill factor (f.f) on the sensor performance including dispersion curve, sensitivity, FWHM, MRR and resonance angle which leads to achieve a high performance LSPR with adjusting f.f and operating wavelength. Figure 1. Proposed model for subwavelength grating based SPR sensor II. MODELING AND SIMULATION A schematic diagram for our SPR biosensor device is shown in Fig. 1. It shows a krestchmann configuration in combination with a nanograting structure on top of it. In the diagram, dm is the intermediate metal layer thickness which is stetted to 40nm. As shown in Fig. 1 this thin gold film layer is placed on a SF10 glass substrate with the refractive index of p n after a 2-nm thick chromium International Journal of Electronics and Electrical Engineering Vol. 4, No. 4, August 2016 ©2016 Int. J. Electron. Electr. Eng. 318 doi: 10.18178/ijeee.4.4.318-321