Charge-Coupled Device


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[[Image:CCD charge transfer animation.gif|frame|left|Animation by Michael Schmid, Charge transfer in a three-phase CCD]]
[[Image:George E Smith.jpg|thumb|right|George E. Smith]]  
[[Image:George E Smith.jpg|thumb|right|George E. Smith]]  

Revision as of 14:13, 30 January 2014

George E. Smith
George E. Smith

On 29 January 1970, Willard S. Boyle and George E. Smith, of Bell Labs, submitted a paper on their invention of the CCD to the Bell System Technical Journal. Forty years later, their innovation would earn them the 2009 Nobel Prize for Physics.

A CCD is an integrated circuit that captures and stores light and displays it by turning it into an electrical charge. Each CCD chip is composed of an array of Metal-Oxide-Semiconductor (MOS) capacitors, and each capacitor is a pixel. When electrical charges, are applied to the CCD’s top plates, they can be stored within the chip’s structure. Then, digital pulses applied to the top plates can shift these charges among the pixels, creating a picture representing charged pixels.

These photoelectric image sensors made digital photography possible, and revolutionized astronomy, space science, and consumer electronics. The CCD is a crucial component of fax machines, digital cameras, and scanners.

The CCD was originally envisioned as a device for storing memory. Boyle and Smith applied the concept of a “Bucket-Brigade Device” (BBD) that would transfer charge packets from one transistor to another create a transport mechanism for capacitors, or “magnetic bubbles.”

Ironically, CCD sensors were an offshoot of Bell Labs’ failed effort to develop the Bell Picturephone, a television phone based on a silicon diode array camera tube. The device was impractical because it required millions of silicon diodes to mass produce, and, as George E. Smith recalled, “just one bad diode caused by imperfections in the silicon would short out the diode, and therefore it couldn’t be used as a detector.”

As interest in the picture phone waned, Bell Lab applied its underlying technology towards the development of Boyle and Smith’s magnetic bubble idea. The goal was to create a shift register using semiconductors. 

With the publication of Boyle and Smith's research in 1970, other scientists began experimenting with the technology on a range of applications. Astronomers discovered that they could produce high resolution images of distant objects, because CCDs offered a photosensitivity one hundred times greater than film. “The major thing is the quantum efficiency. You can close to 80 percent quantum efficiency in a CCD,” George E. Smith would later explain. “With the good CCDs, eight out of ten photons coming in would make an electron that can be read out and counted. With the photographic film a hundred photons need to come in before it breaks one of the bonds in the silver halide so that can be developed.” CCD technology was integral to the design of the Hubble Space Telescope’s Wide Field and Planetary Camera, which contained eight CCDs. CCDs were also first installed in a reconnaissance satellites in December 19176.

In the 1970s, consumer electronics companies experimented with CCD technology in still and video cameras. In 1971, Bell Labs researcher Michael Tompsett received first patent (4,085,456) on the application of CCDs to imaging. He produced images using a simple linear device. In 1975, Kodak’s Steven Sasson would invent the first digital still camera using CCD technology developed by Fairchild Semiconductor. By the late 1970s, Sony was pioneering the use of CCDs in video cameras; this research led to the mass production of camcorders in the 1980s.

Further Reading: