CMOS Imagers Offer CCD Quality

Semiconductor International: "I believe that CMOS active pixel sensors will replace CCD devices in all applications except those requiring the highest signal-to-noise ratio and uniformity or optimal detectivity in dark conditions." IBIS 1 is being manufactured by Alcatel-Mietec (Oudenaarde, Belgium) in its standard 0.7 mm technology. IMEC now plans to improve the image resolution of IBIS 1 and to incorporate color filters on the chip. Economical CMOS devices have many potential applications including multim

Staff -- Semiconductor International, 2/1/1998

1. The potential barrier formed by the p⁺ layer results in charge carriers moving into the useful junctions.

The on-chip integration of the double sampling circuitry eliminates the nonuniformities that are normally unavoidable in CMOS technology. They can produce a fixed pattern noise as a "snow-like" effect over the image. Correction electronics are implemented for each image column to ensure that no new nonuniformities are introduced. The corrections are executed at the same speed as the image data transfer rate.

2. This IBIS 1 sensor is fabricated in standard CMOS technology

IBIS 1 uses an array of 386 x 290 square pixels on a 14 µm pitch. Each pixel has three transistors. The sensor provides an image rate of at least 50 Hz and a dynamic range of 1:2800. It also contains an electronic shutter. CCD devices require optimized production technology, available from few manufacturers, but IBIS 1 can be produced by standard silicon processing. CCD devices offer lower dark currents of a few pA/cm², while CMOS sensors typically reach 725 pA/cm² with 30 pA/cm^2, a possible goal. A device containing a 2000 3 2000 sensor array has been tested.

At the IMEC Annual Research Review Meeting in November, Bart Dierickx, leader of the Optical Sensor group, told Semiconductor International: "I believe that CMOS active pixel sensors will replace CCD devices in all applications except those requiring the highest signal-to-noise ratio and uniformity or optimal detectivity in dark conditions."

IBIS 1 is being manufactured by Alcatel-Mietec (Oudenaarde, Belgium) in its standard 0.7 mm technology. IMEC now plans to improve the image resolution of IBIS 1 and to incorporate color filters on the chip. Economical CMOS devices have many potential applications including multimedia, consumer video cameras, digital photography, sur veillance and automotive uses. Unlike CCD devices, other circuitry can easily be integrated onto IBIS 1 to form a single chip camera. BD

Semiconductor International / February 1998