Example of low light image. Source Fraunhofer Institutes

Certain CMOS applications require pixels in excess of 10µm, compensating for low light in X-ray or astronomy image capture, among other environments. The sensors could also be used as 3D sensors based on the time-of-flight process, whereby 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 3D image. Also read: CMOS image sensors see growth beyond cellphones.

Pinned photodiodes (PPD) convert the light signals into electrical pulses. PPDs encounter a speed problem when the pixels exceed a certain size, said Werner Brockherde, head of department at the Fraunhofer Institute for Microelectronic Circuits and Systems IMS. The read-out speed of PPD cannot keep up with the image-rate demands of these low-light applications, Brockherde explained.

The Fraunhofer optoelectronic component, a lateral drift field photodetector (LDPD) integrates an internal electric field into the photoactive region of the component, Brockherde said. "The charge carriers generated by the incident light move at high speed to the readout node;" with PPD, electrons simply diffuse to the exit comparatively slowly. The Fraunhofer LDPD accelerates this process "by a factor of up to a hundred."

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