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Fraunhofer Group for Microelectronics

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New device brings CMOS chips up to speed

CMOS image sensors are cheap to produce and also superior in terms of power consumption and handling. In applications where only minimal light is available, however – such as astronomy – these semiconductor chips are reaching their limits. This is because large pixels arranged in a matrix do not allow for fast read-out speeds. Researchers at Fraunhofer IMS have now developed an optoelectronic device that speeds up this process.


3D camera module. Photo: Fraunhofer IMS
3D camera module. Photo: Fraunhofer IMS
High-speed CMOS sensors are used here to control production machinery. Photo: Fraunhofer IMS
High-speed CMOS sensors are used here to control production machinery. Photo: Fraunhofer IMS

Most of today’s commercially available digital cameras, and cell phones too, are equipped with CMOS chips. The pixels that these chips work with are sometimes only one μm² in size. For very low-light applications such as astronomy or x-ray photography, however, this is too small. A larger pixel area with an edge lenght of about 10 μm must be used to compensate for the lack of light.

A high-speed trip to the read-out node

In existing CMOS sensors, pinned photodiodes (PPDs) are used to convert the light signals into electrical pulses. These optoelectronic devices are built into the chip and ensure that the charge carriers generated by the light diffuse to the read-out node: a comparatively slow process, but one that is sufficient for many applications. When the pixels exceed a certain size, however, the PPDs can no longer read out the image rates fast enough. Researchers at the Fraunhofer Institute for Microelectronic Circuits and Systems IMS now have a solution to this problem – it is unique and has already been patented. The scientists have developed a new optoelectronic device: the lateral drift field photodetector (LDPD), which allows for much faster reading. “By integrating an internal electric field into the photoactive region of the device, we have managed to accelerate this process by a factor of up to a hundred,” explains Werner Brockherde, head of department at Fraunhofer IMS.

First prototype available

Naturally, the additional LDPD component must not be allowed to impair the properties of the other devices. Using simulation calculations, the experts succeeded in meeting these requirements. A prototype of the new high-speed CMOS image sensors is already available, and series production of the LDPD is planned to begin during the year. The improved CMOS chips could be used in astronomy, modern x-ray photography, or even production technology. These chips are also ideally suited for use as 3D sensors based on the time-of-flight process. Light sources emit short pulses that are reflected by objects. The time of flight of the reflected light is then recorded by a sensor and used to create a full-fledged 3D image. This technology is a compelling proposition for applications such as crash protection. The Duisburg-based researchers have already developed this kind of area sensor for TriDiCam GmbH, a spin-off company of Fraunhofer IMS.


Werner Brockherde
Phone +49 203 3783-230
Fraunhofer Institute for Microelectronic
Circuits and Systems IMS
Finkenstrasse 61
47057 Duisburg