FujiFilm Develops Organic Imaging Sensor

April 1, 2006: Fuji Photo Film in Japan has developed a CMOS sensor using an organic photoelectric conversion film, which has potential for use in digital cameras.

The new sensor, which was first announced at the IS&T/SPIE Electronic Imaging Science & Technology conference in January, evolved from previous research, which used an organic photoelectric conversion film in combination with an imaging tube. So far, developers have only been able to record a monochrome image with it. According to a report in Nikkei Electronics Asia, it was produced by encapsulating the organic photoelectric conversion film with a signal read circuit (made with CMOS technology) into a semiconductor package, making it much easier than an imaging tube to use in a compact consumer camera.

Fuji Photo Film has not disclosed when the organic CMOS sensor might be commercialised but the development is seen as a major step towards a sensor that could be the ideal imaging device. Significantly, the image was output using a standard signal read circuit and a green organic photoelectric conversion film. A development from the prototype would use all visible light thanks to a vertical stack of organic photoelectric conversion films. (Red and blue organic photoelectric conversion films would be required in the final products.)

CMOS sensors with photoelectric converters for each colour aligned vertically have already been commercialised by Foveon Inc of the US. However, the wavelength sensitivity of each converter is low, so special image processing is required to obtain accurate colours. Fuji Photo Film’s organic CMOS sensor, on the other hand, offers wavelength selectivity close to that of silver nitrate film and its per-pixel optical utilisation is tripled, making it possible that sensitivity would be significantly higher than that of existing imagers.

Organic CMOS sensors are likely to also offer advantages in terms of aperture ratio (the portion of each pixel actually used for photoelectric conversion) and cost reduction. In the Fuji Photo Film prototype, the aperture ratio is said to be close to 100% because the photoelectric conversion film is the first thing the incoming light encounters. The signal read circuit lies behind it. This means no microlenses would be needed and production costs could be reduced. (In existing CMOS sensors, the photoelectric converter is partially obscured by the signal read circuit.)