We’ve come a long way since the CCD (charge-coupled device) sensors used in the first digital cameras. Backside-illuminated (BSI) sensors and stacked chips are now the headline items in promotions for the latest cameras. In this feature we’ll look at how different sensor technologies work. Some basics are outlined in the box on this page.
Backside-illuminated (BSI) sensors use the same structural elements as older sensors with front illumination but put the wiring behind the photo-detector layer. The reverse side of the chip was thinned so that light can reach the photo-detectors directly.
Sony introduced its first Exmor-R consumer-level BSI sensor in August 2009. The new chip roughly doubled the sensor’s low-light performance and was soon used in the company’s cameras and smartphones.
BSI sensors can usually cut image noise by the equivalent of about one f-stop, which means a BSI chip would show a similar level of noise in an image
