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Why Is A Backside Illuminated Sensor More Sensitive Than A Front Side Illuminated Sensor?

Source: PCO-TECH Inc.
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Backside illuminated image sensors have fewer obstacles in the pathway of the incoming light as it reaches the volume of the pixel, where the conversion to charge carriers takes place. As a result, backside illuminated CMOS image sensors are able to convert more of the light into charge carriers, resulting in larger signals and better images.