This contribution describes the modeling of CMOS image sensors employed in time-of-flight (ToF) sensor systems for 3D ranging applications. Our model relies on the theoretical description of photo-generation, charge transfer including diffusion, fringing field, and self-induced drift (SID). This method makes it possible to calculate the time-dependent charge carrier generation, transfer, and distribution. The employed approach allows elimination not only of irradiance-dependent charge transfer, but also of undesired reflectance effects, and the influence of ambient light through an in-pixel background measurement. Since the sensor is operated with very short integration times it is crucial to accomplish a fast transfer of the generated charge from the photodetector to the sense node, and speedy conversion into an electrical signal at its output. In our case, we employed a lateral drift field photodetector (LDPD), which is basically a pinned photodiode with a built-in drift field formed by a doping gradient. A novel pixel structure is presented which is optimized for a fast charge transfer by the appliance of the shown model. Numerical calculations predict a two times faster charge collection.

Date Published: 5 May 2015
PDF: 9 pages
Proc. SPIE 9506, Optical Sensors 2015, 950603 (5 May 2015); doi: 10.1117/12.2178390

Published in SPIE Proceedings Vol. 9506:
Optical Sensors 2015
Francesco Baldini; Jiri Homola; Robert A. Lieberman, Editor(s)