Process enables integrating color sensors at CMOS level
Color sensors are required for many applications. One of the most important is color control in displays and LEDs. To date, components with complex nanoplastic structures are used for this purpose. They filter the incident light in such a way that only defined parts of the color spectrum reach the detector surface. The angle of incidence of the light is decisive for functional color filtering. In order to avoid light from unwanted angles and thus color errors, the sensors are combined with macroscopic elements to improve filter accuracy. The disadvantage is that they significantly increase the overall size of the structure. In the joint development project FOWINA, the Fraunhofer Institutes for Integrated Circuits (IIS) and for Silicate Research (ISC) have developed an all-in-one solution that combines many functions in a minimum of space.
The color sensor chip integrates color filter structures, angle filters for controlling the incidence of light, evaluation electronics for signal processing, and photodiodes for converting light into electricity. Due to their very compact design, the new color sensors allow an ultra-flat design, so that they can be used in many products such as cameras or mobile phones. In addition to the high degree of integration, which combines as many functions as possible in a small area, the scientists also succeeded in simplifying production. The sensors can thus be manufactured and sold much more cost-effectively than with previous processes.
The Fraunhofer IIS (Erlangen, Germany) is developing the sensor chip including the nanoplasmic color filters. These can be produced cost-effectively in the CMOS process together with photodiodes and evaluation electronics using a single technology on a common silicon chip. The Fraunhofer ISC (Würzburg, Germany) has developed arrays of microstructures that act as angle filter elements for the sensors. The scientists used two-photon polymerization for this purpose. With this modern technology, microstructures of any shape and structured surfaces can be produced. To accelerate the manufacturing process, the Fraunhofer ISC uses nanoimprint technology – a high-precision, production-proven molding process – to replicate the structures. This technique allows different structures to be combined in a single substrate.
As part of the development project, the Fraunhofer ISC was able to use micro-optical structures to limit the angle of incidence of the light to a range of +/-10 degrees so that the best possible color filtering is achieved. This enables users, for example, to actively adjust the color of LEDs. In addition, the microlenses offer very high surface accuracy so that the light hits the color filters specifically. For the arrays, a special inorganic-organic hybrid polymer is used that is characterized by very high chemical, thermal and mechanical stability and can be adapted easily to specific requirements by modifying the molecular structure.
Currently, the two Fraunhofer partners are optimizing the development and manufacture process of the sensors in order to enable industrial-scale mass production.
Related articles:
3D printer creates color through nanostructures
Color sensor addresses high-end consumer, industrial apps
If you enjoyed this article, you will like the following ones: don't miss them by subscribing to :
