Canadian Inventions —The Charge-coupled Device (CCD)

A charge-coupled device (CCD) is an electronic circuit that converts light energy into an electrical signal. Originally developed as a form of bubble memory (an alternative to the hard drives developed during the 1970s), CCDs are now one of the most prevalent forms of image sensor used in digital cameras. CCD sensors ‘capture’ an image by converting light into electrical charge. The charge is stored temporarily in a matrix of photoactive capacitors embedded in the surface of the CCD before being transferred to auxiliary electronics for processing and storage. Willard Boyle and George Smith first conceived the CCD in 1969, while working at AT&T Bell Labs in Murray Hill, New Jersey. Both men were established physicists. Boyle, originally from Amherst, Nova Scotia, had studied at McGill University and taught at the Royal Military College of Canada before taking a position with Bell Labs in 1953. He had invented the continuous ruby laser (the first laser to be used in medicine) in 1962 and contributed to the Apollo space program as the director of Space Science and Exploratory Studies at Bellcomm (a Bell Labs subsidiary). Smith, a native of White Plains, New York, received his PhD from the University of Chicago before starting work at Bell Labs in 1959. He had also been involved with the laser development programme at Bell Labs before shifting to work with integrated circuit alongside Boyle in the late 1960s. Boyle and Smith were working on semiconductor bubble memory when they conceived the CCD sensor. Although they originally designed the CCD for shifting bits within a memory array (a device known as a ‘shift register’), the pair quickly identified the applicability of the concept to electronic imaging. Their first lab book entry explained how the photoactive semiconductor capacitors at the heart of the CCD circuit became charged by incident light and were able to be discharged in sequence by the ‘shifting’ function of the CCD circuit (allowing the CCD to transfer imaging information to auxiliary electronics). The first CCD sensor capable of capturing images was produced by Bell Labs in 1971. It had a sensing surface formed from photoactive semiconductor capacitors that became charged when exposed to light; with the charge induced in each capacitor being proportional to the intensity of the light. After an image had been ‘captured’ by the sensor, the charge in each capacitor was transferred from the sensor in sequence so that the image could be patched together from individual pixels (the individual capacitors) by auxiliary electronics. CCD development progressed rapidly after the first digital camera was produced by Kodak in 1975 using a CCD sensor. In 1976, the US launched the first real-time optical reconnaissance satellite (the KH-11 KANNAN) employing CCD digital imaging. Early consumer digital cameras (produced in the 1980s and 1990s) were almost exclusively based on CCD technology and contemporary high-end digital cameras still rely on CCD sensors. Following the wide spread adoption of the CCD sensor in the early 1970s, Boyle became the Executive Director of Research at Bell Labs. He remained in the position until his retirement and return to Nova Scotia in 1979. Smith remained with Bell Labs until 1986, when he left to sail around the world. (Interestingly, both men had served in their respective navies in WWII and both remained avid sailors). For their work on the CCD, Boyle and Smith received numerous prizes, including the 2009 Nobel Prize in Physics. Summary by: Richard Murphy