A picture is worth a thousand words. Transcending languages, they cross oceans, reach out from space and show us inside the human body. In December, the winners of the 2017 Queen Elizabeth Prize for Engineering will receive their award at Buckingham Palace. They are to be honoured for creating digital imaging sensors. Together, they have revolutionised the way we see and capture the world around us.
Digital imaging allows people worldwide access to a vast array of pictures and videos. They have enable high-speed, low-cost colour imaging at a resolution and sensitivity that can exceed that of the human eye. From snaps of individual cells to stars billions of light years away, image sensors have transformed our lives.
To find out how it all began, we must travel back to 1969, to a lab in New Jersey. Here, two engineers were tinkering away at improving computer memory. George Smith and Willard Boyle invented a device that could move and manipulate electrical charge. Their charge coupled device, the CCD, converted electrical signals into digital data. It wasn’t until the following year that a young British engineer recognised the device’s potential.
Improving the charge coupled device
As a young engineer working at AT&T Bell Laboratories, Tompsett came across Smith and Boyle’s work and immediately saw its use in imaging. He took Smith and Boyle’s CCD and added an imaging semiconductor circuit and analogue-to-digital converter. The imaging CCD works by capturing particles of light, or photons, in sensitive areas called ‘pixels’. When light hits the sensors, they release an electrical pulse. The brighter the light is, the stronger the electrical pulse produced. An analogue-to-digital converter than transforms the pulse into a simple binary code, to be stored as digital data.
Tompsett’s imaging CCD has become ubiquitous around the world. As well as featuring in all early digital cameras, it set the foundations for today’s cameras and smartphones. In 1980, Nobukazu Teranishi improved the CCD with the pinned photodiode. A photodiode is a semiconductor that, when exposed to light, lets current to flow in one direction only. They work rather like a one-way valve for electricity. Teranishi’s PPD proved more efficient and sensitive than previous photodiodes. This shrank the size of pixels, fitting more into the same area and resulting in higher resolution images.
Shrinking cameras for space travel
The final piece of the puzzle fell into place with the work of Eric Fossum at NASA’s Jet Propulsion Laboratory. Tasked with shrinking CCD-based cameras for space travel, Fossum created a new sensor. Like the CCD, Complementary Metal Oxide Semiconductors, or CMOS sensors, use pixels to produce a current. Unlike CCDs, the second-generation sensor has transistors at each pixel to amplify and move charge. This means not only can sensors be shrunk to fit on a fingertip, they use 100 times less power than CCDs. CMOS chips proved cheap to produce and paved the way for cheaper cameras with better battery life. They have made photography accessible to everyone.
Throughout November, we are turning the page to the next chapter. Billions of sensors are produced every year for use in medicine, space exploration, transport, communication and entertainment. This month, we are taking a snapshot of some of the applications of this ground-breaking engineering innovation. Follow us on Twitter, LinkedIn and Instagram to find out how image sensors have changed the world.
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