Front-illuminated sensor	Backside-illuminated sensor

Sony announced a back-illuminated CMOS sensor promising nearly double the sensitivity of its current CMOS chips along with lower noise in images. Traditionally, front-illumination technology has been used for imaging sensors. According to Sony, though, back-illuminated sensors will deliver improved performance in both digital cameras and camcorders
The back-illuminated (or backside-illuminated) technology concept isn't new, but using it to provide acceptable levels of sensitivity and noise would be. Past incarnations have led to increased noise and image degradation, but Sony claims its new model has made changes to eliminate these issues. Read the whole article here