Back-illuminated sensor

The technique was used for some time in specialized roles like low-light security cameras and astronomy sensors, but was complex to build and required further refinement to become widely used.

[1][2] BI sensors from OmniVision Technologies have since been used in consumer electronics from other manufacturers as in the HTC EVO 4G[3][4] Android smartphone, and as a major selling point for the camera in Apple's iPhone 4.

[7] This change can improve the chance of an input photon being captured from about 60% to over 90%,[8] (i.e. a 1/2 stop faster) with the greatest difference realised when pixel size is small,[citation needed] as the light capture area gained in moving the wiring from the top (light incident) to bottom surface (paraphrasing the BSI design) is proportionately larger for a smaller pixel.

Orienting the active matrix transistors behind the photocathode layer can lead to a host of problems, such as crosstalk, which causes image noise, dark current, and color mixing between adjacent pixels.

[8] Other advantages of a BSI sensor include wider angular response (giving more flexibility for lens design) and possibly faster readout rates.

The ability to collect more light meant that a similarly sized sensor array could offer higher resolution without the drop in low-light performance otherwise associated with the megapixel (MP) race.

[19] In April 2021, Ricoh released the Pentax K-3 III featuring a BSI 26 megapixel APS-C sensor from Sony and a PRIME V image processor.

[20] Stacked CMOS also allows more complex processing circuitry to be used simply by increasing the layer count, enabling faster frame rates and readout speeds.

[22] In April 2021, Canon announced their new EOS R3 would feature a 35mm full-frame, back illuminated, stacked CMOS sensor and a DIGIC X image processor.