Back‑Illuminated (BSI) Pixels: Underlying Hardware Foundation for High‑Sensitivity & Low‑Noise Multispectral Sensors

Multispectral sensors require simultaneous light sensing under low‑light, high‑speed and multi‑band conditions. Traditional Front‑Illuminated (FSI) CMOS pixels feature circuit layers blocking photosensitive layers, causing heavy photon loss and high noise that fail strict multispectral requirements.Back‑Illuminated (BSI) pixels, the core hardware architecture for global multispectral sensors first commercialized by Sony, have become an industry universal standard.

Core principle: For traditional FSI pixels, light must pass through metal circuit layers to reach photodiodes with massive photon blocking and reflection. BSI architecture flips the wafer, placing thephotosensitive layer on the chip front and the circuit layer on the back. Light enters the photosensitive layer directly without obstruction, boosting photon utilization by over 40% and greatly improving low‑light sensitivity. Three core advantages for multispectral scenarios: First,multi‑band spectral consistency—filters paired with BSI pixels deliver uniform light sensing across bands without inter‑band noise differences. Second,high dynamic range (HDR)—strong high‑light suppression adapts to industrial intense light, automotive backlighting and complex outdoor lighting. Third,low readout noise—suitable for high‑speed snapshot imaging to ensure precise single‑frame multi‑band data acquisition. Currently, Sony IMX454, Imec consumer‑grade chips, Fujitsu infrared sensors, Huawei mobile spectral sensors and Tesla automotive sensorsall adopt BSI pixel architecture, the underlying hardware guarantee for large‑scale multispectral commercialization.