Near-Infrared Sensitivity Enhancement of Image Sensor by 2ND-Order Plasmonic Diffraction and the Concept of Resonant-Chamber-Like Pixel

We propose $2^{\text {nd}}$-order plasmonic diffraction and the concept of a resonant-chamber-like pixel to enhance the near-infrared (NIR) sensitivity of Si image sensors. It is demonstrated that $2^{\text {nd}}$-order plasmonic diffraction is efficient and requires less fine patterning. Highly reflective metals such as Ag, Cu, and A1 are suitable for use as buried materials within deep trench isolation (DTI) and can yield high NIR sensitivity. Good Si absorptance can be achieved if a pixel acts as a resonant chamber. In the simulation, Si absorptance as high as 49% at 940 nm wavelength for $3.25-\mu \mathrm{m}$-thick Si is obtained.