Plasmonic diffraction for the sensitivity enhancement of silicon image sensor

Introduction Near-infrared (NIR) sensing technology has been extensively applied in biological inspection, Timeof-Flight (ToF), surveillance, and fiber optic communication. A wavelength of 940 nm is mostly used as their light source, because it is completely invisible to the human eye and is less affected by sunlight. However, silicon-based image sensors have insufficient sensitivity in NIR region because of the low silicon absorption. Although a thick silicon absorption layer improves NIR sensitivity, this approach degrades image recognition due to the crosstalk between pixels and is technically difficult to be implemented in deep trench isolation (DTI). Therefore, improving the NIR light sensitivity without a thick silicon layer is a significant issue. In recent years, a multiple pyramid shape surface of silicon sensitive layer has been proposed and developed to increase the light propagation length and effective silicon thickness by light diffraction [1]. Applying plasmonic enhancement also has the potential to improve the NIR sensitivity of sensors. Plasmonics has been applied in the photonics research field, ranging from ultraviolet to infrared, such as fluorescence enhancement, surface enhanced Raman scattering, solar cells, color filters, and thermal emission control. In sensor applications, the development of silicon metal Schottky junctiontype photodetectors using plasmon hot carriers and enhanced electric fields by surface plasmon resonance have attracted attention in the detection of photon energies below silicon bandgap of 1.12 eV [2-8]. Most of the approaches in plasmonics to photonics applications have included the utilization of strong electric field enhancement, which involves resonant coupling between photons and electrons in metal. In this study, we apply the quasiresonant conditions of surface plasmons to improve the silicon absorption efficiency [9].