Vision sensor operates in high and low temperatures

Paul Boughton
Image sensors for use as electronic parking aids in cars or for quality control in production systems have to be able to withstand the often very high temperatures that prevail in these environments. Research scientists from the Fraunhofer Institute have produced a CMOS chip that functions even at a temperature of 115 degrees C.
Parking sensors must be able to function in high temperatures and in bright sunlight; if they are installed behind the rear view mirror or on the instrument panel, for example, they can get very hot. The Fraunhofer Institute for Microelectronic Circuits and Systems (IMS) has developed a high-temperature CMOS (complementary metal oxide semiconductor) image sensor for an industrial customer; this device can withstand temperatures ranging from -40 to +115 degrees C. In contrast, the CCD (charged coupled device) image sensors currently available will typically fail when the temperature exceeds approximately 60 degrees C. Werner Brockherde, department head at the IMS, states: "Our chip is not only heat-resistant, it even functions at arctic temperatures."
The research scientists have succeeded in developing pixels that exhibit an extremely low dark current. This reduction of residual current, which flows in complete darkness, makes it possible to capture very high-quality images even in extreme heat. Brockherde explains: "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 artefacts or fuzziness and degrades the image."
A further special feature of the sensor is its image size of 2.5 x 2.5cm. This offers the advantage that, for special applications with weak illumination or for capturing images in the infrared 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 decibels provides increased contrast and optimised 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. Furthermore, the chip supports cameras with synchronous as well as asynchronous shutters. The synchronous shutter prevents motion artefacts, 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 minimise image noise.
Brockherde comments: "We produced the sensor in a standard process using 0.5 micrometre CMOS technology in our own semiconductor factory. We also produce special components here for industrial customers." 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 new CMOS image sensor will be on show at the Vision trade fair from 9-11 November 2010 in Stuttgart (Stand 6 D12).
For more information, visit

Recent Issues