Education
From ITLWiki
CCD Operation
The movie below shows a simple demonstration of the operation of a CCD. You can think of CCDs as an array of buckets (pixels) out to catch rainfall (photons of light). The red buckets are just like pixels of a CCD imaging area. The purple buckets are the readout or serial register. At the end of the row of purple buckets is a metering station (the output amplifier) where the rain water is measured. The values of each bucket are read out to a computer. The computer then assigns gray-scale values to each number (in the movie, 1 is white, 3 is black, with variations of gray in between) and reconstructs the image.
Why thin (or back-illuminate) a CCD?
Backside access of light (photons) into silicon is the main reason charge-coupled devices are thinned or back-illuminated. Front-illuminated CCDs absorb and reflect much of the incident light due to pixel structures and electrical circuits near the frontside surface. If the CCD is flipped over to expose its backside to light, the photons are better able to enter the silicon. The device is then made very thin so that the electrons generated by the incident light are not impeded by traps within the silicon. These electrons can then easily travel to the pixels near the front side of the CCD where they are detected to form an image. The application of an antireflection coating to the back surface reduces the number of photons lost to reflection before entering the silicon.