100x Sensitivity Image Sensor Based on Solar-cell Structure

Apr 18, 2008
Yukiko Kanoh, Nikkei Electronics
Comparisons of photos shot in a dark room
Comparisons of photos shot in a dark room
[Click to enlarge image]

Rohm Co Ltd and the Research Center for Photovoltaics of the National Institute of Advanced Industrial Science and Technology (AIST) have announced that they have succeeded in prototyping a CIGS (Cu-In-Ga-Se) image sensor that has approximately 100 times the sensitivity of CCD, CMOS and other Si-based image sensors.

They have confirmed that their sensor can recognize images in environments as dark as 0.001lx, which is difficult for existing Si image sensors, they said. As the new image sensor can also recognize images with light in the near infrared zone, expected applications include automotive cameras, monitoring cameras, iris and vein authentication, which must support image sensing under lighting conditions ranging from bright to dark.

Image recognition under 0.1lx or lower light is difficult for Si image sensors that are generally used for automotive and night-vision cameras today. Rohm and the AIST have been, therefore, developing an image sensor that adopts the CIGS, which boasts about 100 times higher light absorption coefficient compared with the Si, as a light sensitive element.

The photodiode used in this sensor seems to have the same technical structure as that of CIGS solar cell systems. The companies succeeded in amplifying electric charges converted from photon in the device and increasing the sensitivity to roughly 100 times that of Si image sensors. They explained the success is attributed to the optimization of ratios of the material composition and the improved process technology.

Rohm will further advance the development toward commercialization by (1) increasing resolution through miniaturization and (2) reducing the variation of pixels through more stabilized process technology, for example, it said.

Rohm and the AIST already showcased a reference image sensor based on CIGS compound at CEATEC Japan 2007 in October 2007.