Clever cars get color cameras

Krista D. Zanolli, krista.zanolli@laurin.com

In a move that is reminiscent of the 1980s hit series Knight Rider, researchers at the Fraunhofer Institute for Microelectronic Circuits and Systems IMS in Duisburg have developed a process that will give a futuristic boost to in-car driver assistance systems.

Thanks to high-tech cameras, the car of the future will help park itself, warn the driver of blind spots or obstructions, and even recognize traffic signs.

Driver assistance systems typically come equipped with special cameras housing CMOS image sensors that convert light signals into electrical pulses. These sensors have limited sensitivity to light, however, and are essentially color-blind, providing only monochrome images. Regardless, the sensors are expected to meet a wide range of requirements. They must be small, light and yet tough enough to endure high ambient temperatures. Additionally, they must reliably capture all the required images and should cost as little as possible.

The innovative CMOS image sensor can distinguish color and is much more light-sensitive than conventional sensors. Image Fraunhofer IMS.

Now, however, Fraunhofer researchers are boasting a new production process that makes these sensors much more sensitive to light and allows them to recognize and distinguish color.

“We have integrated a color filter system in the process,” explains Dr. Holger Vogt, deputy director of IMS. “In the same way as the human eye needs color-specific cone types, color filters have to be inserted in front of the sensors so that they can distinguish color.”

This is done by coating each pixel on the sensor with a micrometer-thick layer of polymer dyed in the primary color of red, blue or green. A mask that is transparent only on the desired pixels and UV light are used to fix the dye at the requisite points, and the rest is washed off.

In addition, special microlenses have been developed to help the sensor capture and measure light more efficiently. With the aid of a transparent polyimide, the investigators created a separate lens for each individual pixel, almost doubling the light sensitivity of the image sensor.

According to the researchers, the optimized CMOS process not only makes cost-efficient driver assistance systems possible, but it could also improve endoscopic probes.