A New Analytical Charge Transfer Model for Time-of-Flight Image Sensors

A powerful tool for analyzing the performances of an image sensor designed for time-of-flight measurement purposes, the impulse response measurement (IRM), is presented. A way to measure the charges diffusion time (time for the to be collected by the photodiode) using the analysis of an IRM is given. An unexpected phenomenon that occurs when performing a specific IRM is then showcased: performing two successive transfers, a short duration one followed by a long duration one is actually less efficient than performing a single transfer of long duration (same duration as the second transfer in the first case). Accordingly, a mathematical sufficient condition on the charge transfer efficiency function (CTEF) is enounced. A physical modeling based on thermionic emission theory and the influence of the potential barrier's width on its effective height is presented. The model leads to a new CTEF expression that fulfills the mathematical requirement. Finally, a numerical simulation with the new CTEF fitting the experimental IRM data is performed.