Definition of back-side illumination

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Photonics Dictionary

back-side illumination: Back-side illumination (BSI) is a technology used in imaging sensors, particularly in digital cameras, where the light is allowed to enter the sensor from the back side, opposite to where the electronic components are located. This design improves the amount of light that reaches the photosensitive area of each pixel, enhancing the sensor's efficiency and performance, especially in low-light conditions.

Light path: In traditional front-side illuminated (FSI) sensors, light has to pass through various layers of metal wiring and circuitry before reaching the photosensitive area. In BSI sensors, this obstacle is removed by flipping the sensor, so light directly hits the photosensitive area without interference.

Increased sensitivity: By eliminating the obstruction caused by metal wiring, BSI sensors can capture more light, making them more sensitive and capable of producing higher-quality images in low-light conditions.

Improved image quality: BSI technology generally results in better image quality with reduced noise, higher dynamic range, and better color fidelity due to the increased light sensitivity and reduced interference.

Smaller pixel size: BSI allows for smaller pixel sizes while maintaining or even improving performance, enabling higher resolution sensors without compromising image quality.

BSI technology is widely used in various imaging applications, including:

Smartphones: Enhancing camera performance in compact devices where space is limited.

Digital cameras: Providing better performance in professional and consumer-grade cameras.

Scientific imaging: Used in applications requiring high sensitivity, such as in microscopy and astronomy.

Security cameras: Improving image capture in low-light surveillance situations.

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