High-speed CMOS sensors provide better images

Ashley N. Paddock, ashley.paddock@photonics.com

A patented photodetector that boosts the speed of traditional CMOS sensors now can produce better-quality images for low-light applications such as spectroscopy, astronomy and x-ray photography.

Some CMOS applications require pixels in excess of 10 µm to compensate for low light in x-ray or astronomy image capture. The high-speed sensors could be used as 3-D sensors based on the time-of-flight process.

Pinned photodiodes (PPDs) convert light signals into electrical pulses, but they encounter speed problems when the pixels exceed 10 µm, said Werner Brockherde, department head at Fraunhofer Institute for Microelectronic Circuits and Systems IMS. When pixels exceed a certain size, PPD readout is too slow for low-light applications.

High-speed CMOS sensors are shown controlling production machinery. Courtesy of ©Fraunhofer IMS.

To combat this problem, the scientists developed an optoelectronic lateral drift field photodetector (LDPD) that integrates an internal electric field into the photo-active region of the component, Brockherde said.

“In this component, the charge carriers generated by the incident light move at high speed to the readout node,” Brockherde explained. “But by integrating an internal electric field into the photoactive region of the component, we have managed to accelerate this process by a factor of up to a hundred.”

The researchers improved upon the currently available CMOS chip manufacturing process, based on the 0.35-µm standard, making sure not to impair the properties of the other components by adding the LDPD. Simulation calculations ensured that they met those requirements, and a prototype of the new high-speed CMOS sensor was developed. It is now available, and series production is expected to begin in about a year. The team already has developed time-of-flight 3-D area sensors based on the unique pixel configuration for TriDiCam GmbH.