The CCD was the first practical way to let a light-sensitive silicon chip store an image and then digitize it. In short, it is the basis of today’s digital camera.
The CCD was based on “charge bubbles”, an idea inspired by another project going on in Bell Laboratories at the same time. The sensor is made up of pixels, each of which is a MOS (metal-oxide semiconductor) capacitor. As the light falls on each pixel, the photons become electrons due to the photoelectric effect (the same thing that permits solar power). The photoelectric effect happens when photons of light hit the silicon of the pixel and knock electrons out of place. On a CCD, these electrons are stored in a “bucket”: the pixel’s capacitor.
At this stage, the “image” is still in analog form, with the charge, or amount of electron in the bucket, on each pixel directly corresponding to the amount of light that has hit it. The genius of Boyle and Smith’s CCD was the reading of the information stored.