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Large area color sensor goes vertical

19 Jan 2006

A vertically integrated color sensor developed in Germany and the US could enable alias-free high resolution colour CMOS cameras.

Scientists in Germany and the US claim to have made the first large-area color sensor free of aliasing effects by stacking red, green and blue color imaging elements. The 512 x 512 pixel prototype could ultimately help increase the resolution of colour CMOS cameras. (Appl. Phys. Lett. 88 013509)

Typically, color optical sensing involves placing individual red, green and blue filters over three separate pixels to render a single color pixel. However, the lateral displacement can lead to aliasing effects that degrade the final image. The use of very small pixels helps to minimize the effect, but as Dietmar Knipp of the International University Bremen, Germany, explains, the vertical alignment of the color pixels is an attractive alternative.

"Vertical integration of the sensor's red, green and blue channels allows us to fit more sensors on a chip," he told Optics.org. "Sooner or later the technology will move to vertically integrated sensors because it's getting increasingly difficult to put smaller and smaller color filter arrays on a sensor chip."

Made from semiconducting material, the vertically integrated sensor works by detecting color information as a function of depth. Blue light is absorbed by the top diode and green and red wavelengths pass through to silicon carbon and amorphous silicon absorption layers below.

Applications include lab-on-a-chip systems, which could benefit from the sensor's compact design. Knipp and his colleagues from Research Center Jülich, Germany, and Palo Alto Research Center, US, are also looking to combine their vertically integrated array with CMOS technology.

"At the moment we are trying to get in touch with different CMOS manufactures to put the vertical sensors on top of CMOS readout electronics," Knipp revealed. "Such devices would be of particular interest for camera applications." He feels that prototypes could be rolled-out within the next 12-18 months.


Author
James Tyrrell is news editor on Optics.org and Opto & Laser Europe magazine.

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