The failed memory idea that became the eye of digital cameras
In 1969 two Bell Labs engineers were trying to build a new kind of computer memory based on magnetic bubbles. They realised a packet of electric charge could stand in for a bubble and be passed down a row of tiny capacitors. Forty years later that trick earned them a Nobel Prize.
Willard Boyle and George E. Smith sketched the idea in a notebook under the heading "Charge 'Bubble' Devices". Their insight was that a small metal–oxide–semiconductor capacitor could hold charge, and that lining many of them up and applying the right voltages would shuffle that charge from one to the next. A paper in April 1970 suggested three possible jobs for it: memory, a delay line, or an imaging device.
Imaging won. That same April, Gil Amelio, Michael Tompsett and Smith demonstrated a row of closely spaced metal squares on oxidised silicon, and in August they reported an 8-bit shift register built as an integrated circuit that doubled as a crude eight-pixel imager. By 1971 Tompsett's team at Bell could capture pictures with simple linear devices. Fairchild, under Amelio, sold the first commercial versions and by 1974 offered a 100 × 100 pixel chip. Kodak's Peter Dillon laid a colour filter over that chip to make the first colour CCD sensor, and in 1975 Steven Sasson used the same part in a digital still camera.
Spy agencies were early customers: the first KH-11 KENNEN satellite, launched in December 1976, carried an 800 × 800 array. Sony, pushed by Kazuo Iwama, invested heavily until it could mass-produce CCDs for camcorders, though Iwama died in August 1982 before that happened. Lag in early sensors was largely cured by the pinned photodiode, devised at NEC in 1980.
In a working sensor, a lens throws light onto the capacitor array and each one builds up charge in proportion to the brightness falling on it; the chip then marches those packets out to be read. Boyle and Smith shared the Nobel Prize in Physics in 2009. CCDs still serve demanding scientific and medical work, but since the late 2010s cheaper CMOS sensors have largely replaced them.
Source: Charge-coupled device
