Charged-coupled device

The charge-coupled device emerged because Bell Labs was trying to build a better memory chip and accidentally invented digital imaging. On October 17, 1969, Willard Boyle and George Smith sketched out the CCD concept in about an hour—and built a working prototype within a week.

The context was magnetic bubble memory. Jack Morton, Bell Labs' vice president of Electronics Technology, had tasked Boyle and Smith with creating a solid-state alternative to this emerging technology. Bubble memory stored data as magnetic domains that could be moved through a crystalline substrate. Boyle and Smith realized that electric charge could serve as the analog of the magnetic bubble—and that it could be stored on a tiny MOS (metal-oxide-semiconductor) capacitor.

Their key insight was that charge packets could be transferred sequentially from one capacitor to the next by manipulating voltages—hence 'charge-coupled.' The mechanism resembled a bucket brigade, with electrons passed down a line of potential wells. This made the device useful for both memory (storing and retrieving data) and sensing (converting light into charge).

The first working CCD, reported by Tompsett, Amelio, and Smith in August 1970, was a simple 8-bit shift register with input and output circuits. It was crude—essentially an eight-pixel imaging device—but it demonstrated the principle. Michael Tompsett, a colleague at Bell Labs, recognized the CCD's potential as an imaging sensor and pushed its development in that direction.

The transformation from memory device to camera sensor happened quickly. Several companies—Fairchild Semiconductor, RCA, and Texas Instruments—launched development programs. Fairchild's effort, led by Gil Amelio (himself a former Bell Labs researcher), produced the first commercial devices. By 1974, Fairchild had a linear 500-element sensor and a 2D array with 100 × 100 pixels.

The CCD's advantages over existing imaging technologies were fundamental. Unlike vidicon tubes, CCDs had no lag, no burn-in, and could be manufactured with the same processes used for integrated circuits. They were smaller, more reliable, and could be mass-produced. The same silicon fabrication infrastructure that made computers possible now made digital imaging possible.

The applications cascaded. CCDs transformed astronomy—the Hubble Space Telescope's instruments used CCDs. They enabled medical imaging, barcode readers, fax machines, and eventually digital cameras. Every smartphone camera descends from Boyle and Smith's hour-long brainstorming session.

Recognition came late. In 2006, Boyle and Smith received the National Academy of Engineering's Charles Stark Draper Prize. In 2009, they shared the Nobel Prize in Physics 'for the invention of an imaging semiconductor circuit—the CCD sensor.' A device designed to compete with magnetic bubbles had instead made photography digital.