Fraunhofer IMS develops image sensors for extreme temperatures

The Fraunhofer Institute for Microelectronic Circuits and Systems (IMS; Duisburg, Germany) has developed a CMOS image sensor for an industrial customer that can withstand temperatures ranging from -40 to +115 C. CCD image sensors available up to now fail when the temperature goes beyond about 60 degrees. "Our chip is not only heat-resistant, it even functions at arctic temperatures," says Werner Brockherde, head of the department at the IMS.

The research scientists have succeeded in developing pixels that exhibit an extremely low dark current. This reduction of residual current makes it possible to capture very high-quality images even in extreme heat. "It was not easy to achieve a low dark current. An increase in temperature of just eight degrees doubles the dark current, resulting in image noise and reduced dynamics. Ghosting occurs in the form of artifacts or fuzziness and degrades the image," explains Brockherde.

A further special feature of the sensor is its image size: 2.5 x 2.5 cm. This offers the advantage that for special applications with weak illumination or for capturing images in the IR or UV range the sensor can be connected directly to an electronic image intensifier.

The sensor has a resolution of 256 x 256 pixels. Its high dynamic range or exposure latitude of 90 dB provides increased contrast and optimized detail accuracy both in shadow as well as in very bright areas. Nuances of light are precisely reproduced.

Thanks to its efficient light absorption, the image sensor reacts with high sensitivity even in weak light conditions. It is therefore also suitable for night vision equipment. In addition, the chip supports cameras with synchronous as well as asynchronous shutters. The synchronous shutter prevents motion artifacts, for instance when recording rapid movements, reducing movement fuzziness.

The rolling shutter permits a higher image frame rate and continuous image recording. The effect of this is to minimize image noise. "We produced the sensor in a standard process using 0.5 micrometer CMOS technology in our own semiconductor factory. We also produce special components here for industrial customers," states Brockherde.

In addition to the automotive sector he can see further potential markets, "Our chip is suitable for deployment in chemical and steel production facilities, where it can be used for process and quality control. Very high temperatures prevail, for example, in rolling mills where sheet metal is produced."

The CMOS image sensor will be on show at the VISION trade fair from November 9 to 11, 2010, in Stuttgart (Stand 6 D12).

SOURCE: Fraunhofer IMS

Posted by Conard Holton
Vision Systems Design