Dark current in pinned photodiode CMOS image sensors: a pre-fabrication physics-based model

Abstract

The present technique to find a dark current source in an image sensor, i.e., Dark Current Spectroscopy, is not sufficient to conclusively differentiate between the contribution of interface and bulk defect generation in a pixel. Also, the dark current data is available only post-fabrication. In this work, the Dark current versus Transfer Gate-off voltage curve is used to extract the defect density-cross-section product, activation energy and maximum carrier lifetime for two important device generation sites, i.e., interface under the Transfer Gate and Pinned Photodiode depletion region. A comprehensive analytical dark current model is formulated and validated using TCAD simulation and experimental data reported in the literature. The temperature variation is incorporated using the Arrhenius relation corresponding to the specific activation energy level. The proposed model along with the Arrhenius relation provides a sufficient pre-fabrication dark current estimate.