Taking a major step towards improved CMOS sensors for most in-car camera systems, scientists have developed a new process that could provide colours to these systems. The CMOS sensors are semiconductor chips that convert light signals into electrical pulses and are installed in most digital cameras. However, currently the sensors used for industrial and other special cameras are mostly colour blind.
Now, researchers at the Fraunhofer Institute for Microelectronic Circuits and Systems IMS in Duisburg have developed a new process for producing CMOS image sensors which enables the chips to see colour. Normally the image sensors are produced on silicon wafers using a semiconductor technique, the CMOS process.
“We have integrated a colour filter system in the process. In the same way as the human eye needs colour—specific cone types, colour filters have to be inserted in front of the sensors so that they can distinguish colour,” explained Dr. Holger Vogt, Deputy Director of the IMS. And this done via polymers dyed in the primary colours red, green and blue. Each pixel on the sensor is coated with one of the three colours 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 micro lenses, which help the sensor to capture and measure the light more efficiently. Using a transparent polyimide the researchers create a separate lens for each individual pixel, which almost doubles the light-sensitivity of the image sensor.
The optimised CMOS process not only makes it possible to cost-efficiently improve the performance of driver assistance systems, but the new properties of CMOS image sensors can also boost the efficiency of endoscopes.
The CMOS process was presented at the Vision trade fair from November 3 to 5 in Stuttgart.