Enhancement of Near-Infrared Sensitivity in Silicon-Based Image Sensors to Oblique Chief Rays via Quasi-Surface Plasmon Resonance

A silicon-based image sensor is proposed, incorporating plasmonic diffraction gratings tailored to chief ray angles (CRAs), to enhance near-infrared (NIR) sensitivity improvement over a broad range of incident angles. Under quasi-surface plasmon resonance (quasi-SPR) conditions, the metal grating efficiently diffracted incident light into the silicon absorption layer. The period and width of the metal grating were adjusted at each pixel position according to CRAs, thereby improving the NIR sensitivity at sensor edges. The plasmonically diffracted light with angled chief ray was confined within the pixel photodiode. The photon confinement resulted in a significant improvement in absorption of approximately 37% or more, within an incident angle range of 30 degrees at a NIR wavelength of 940 nm and a silicon thickness of 3 μm. The improvement in NIR absorption over a broad incident angle range enhances the sensitivity of the entire sensor chip, representing a significant advancement for NIR cameras.