The charge-coupled device (CCD)

17 October 1969 (Bell Labs)

Willard Boyle and George Smith invented a chip that stores electric charge in tiny wells and passes it along like buckets in a line. As an image sensor it made digital photography possible.

How it began

At Bell Labs in New Jersey, Willard Boyle and George Smith were asked to come up with a new kind of semiconductor memory. On 17 October 1969, in a short brainstorming session, they sketched a device that stores charge in a row of tiny capacitors and moves it along step by step. They soon saw it could also capture images.

How it works

When light strikes silicon, it frees electrons: the photoelectric effect. Each pixel of a CCD collects these electrons in a potential well, so the charge is proportional to the light. To read the image, voltages on the electrodes shift every charge packet to the next well, row by row, like a bucket brigade, until each reaches a single amplifier at the edge and is measured. See how light becomes an image.

Why it mattered

The CCD was the first practical electronic image sensor. It went into the first digital camera (1975), video cameras, scanners, space telescopes and the first generation of digital still cameras. Boyle and Smith shared the 2009 Nobel Prize in Physics for it.

Limits and what replaced it

CCDs need special manufacturing, use a lot of power and read out slowly through one amplifier. CMOS active-pixel sensors, with an amplifier in every pixel, overtook them in cameras and phones in the 2000s.