Image sensors which are used 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 have produced a CMOS chip which functions even at a temperature of 115 degrees Celsius.

More and more car manufacturers are equipping their vehicles with imagesensors – e.g. to register the presence of pedestrians or vehicles inthe blind spot or to detect obstacles when parking. The sensors must be able to function in extremely high temperatures and in blazingsunlight. If they are installed behind the rear view mirror or on theinstrument panel, for example, they can get very hot. The FraunhoferInstitute for Microelectronic Circuits and Systems IMS in Duisburg hasdeveloped a CMOS (complementary metal oxide semiconductor) image sensorfor an industrial customer which can withstand temperatures rangingfrom -40 to +115 degrees Celsius. The CCD (charged coupled device)image sensors available up to now fail when the temperature goes beyondabout 60 degrees. »Our chip is not only heat-resistant, it evenfunctions at arctic temperatures,« says Werner Brockherde, head ofdepartment at the IMS.

The research scientists have succeeded in developing pixels whichexhibit an extremely low dark current. This reduction of residualcurrent, which flows in complete darkness, makes it possible to capturevery high-quality images even in extreme heat. »It was not easy toachieve a low dark current. An increase in temperature of just eightdegrees doubles the dark current, resulting in image noise and reduceddynamics. Ghosting occurs in the form of artifacts or fuzziness anddegrades the image,« explains Brockherde.

A further special feature of the sensor is its image size of 2.5 x 2.5centimeters. This offers the advantage that for special applicationswith weak illumination or for capturing images in the infrared or UVrange the sensor can be connected directly to an electronic imageintensifier. The sensor has a resolution of 256 x 256 pixels. Its highdynamic range or exposure latitude of 90 decibels provides increasedcontrast and optimized detail accuracy both in shadow as well as invery bright areas. Nuances of light are precisely reproduced. Thanks toits efficient light absorption, the image sensor reacts with highsensitivity even in weak light conditions. It is therefore alsosuitable for night vision equipment. What’s more, the chip supportscameras with synchronous as well as asynchronous shutters. Thesynchronous shutter prevents motion artifacts, for instance whenrecording rapid movements, reducing movement fuzziness. The rollingshutter permits a higher image frame rate and continuous imagerecording. The effect of this is to minimize image noise. »We producedthe sensor in a standard process using 0.5 micrometer CMOS technologyin our own semiconductor factory. We also produce special componentshere for industrial customers,« states the scientist, reflecting theexpertise of the Institute. In addition to the automotive sector he cansee further potential markets: »Our chip is suitable for deployment inchemical and steel production facilities, where it can be used forprocess and quality control. Very high temperatures prevail, forexample, in rolling mills where sheet metal is produced.« The CMOSimage sensor will be on show at the Vision trade fair from November 9to 11, 2010, in Stuttgart (Stand 6 D12).

Source: Fraunhofer-Gesellschaft
Thema: Information and Communication, Micro-Nano-Opto, Transportation and Mobility

• Image sensors for extreme temperatures