CMOS sensors - semiconductor chips that convert light signals into electrical pulses - are used for most in-car systems, and are installed in most digital cameras. At present, however, these sensors used in industrial and other special cameras are mostly color blind.
Now researchers at the Fraunhofer Institute for Microelectronic Circuits and Systems (IMS) in Duisburg, Germany, are adding some color to the picture. They have developed a new process for producing CMOS image sensors which enables the chips to see color. Normally the image sensors are produced on silicon wafers using a semiconductor technique, the CMOS process.
"We have integrated a color filter system in the process," explains Prof. Dr. Holger Vogt, Deputy Director of the 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 job is handled by polymers dyed in the primary colors red, green and blue. Each pixel on the sensor is coated with one of the three colors by a machine which coats the sensor disk propels with a micrometer-thick polymer layer. Using UV light and a mask which is only transparent on the desired pixels, the dye is fixed at the requisite points and the rest is then washed off. In addition, the researchers have developed special microlenses which help the sensor to capture and measure the light more efficiently. With the aid of a transparent polyimide they create a separate lens for each individual pixel, which almost doubles the light-sensitivity of the image sensor.
The optimized CMOS process could also be applied to the cameras used for medical imaging in endoscopes.
Read the full press release from EurekAlert