Photoresponse of CMOS Image Sensors

ii I hereby declare that I am the sole author of this thesis. I authorize the University of Waterloo to lend this thesis to other institutions or individuals for the purpose of scholarly research Signature I further authorize the University of Waterloo to reproduce this thesis by photocopying or by other means, in total or in part, at the request of other institutions or individuals for the purpose of scholarly research. The University of Waterloo requires the signatures of all persons using or photocopying this thesis. Please sign below, and give address and date. iv Acknowledgements I would like to thank Dr. Richard I. Hornsey for the unwavering support, direction, guidance, and encouragements that he has provided throughout this work. The gracious and intelligent manner by which he supervised my postgraduate study is also gratefully appreciated and acknowledged. The fabrication and design support from Canadian Microelectronics Corporation has enabled the experiments carried out in this work. The unwavering help from Jim Quinn at Canadian Microelectronics Corporation is especially noted. Special thanks to my colleagues at VISOR Laboratory at York University for all the memorable and enriching experiences shared over the past several years. Finally, to my parents, my deep thanks and gratitude. Abstract An improved one-dimensional analysis of CMOS photodiode quantum efficiency has been derived in which the effect of the substrate, which forms a high-low junction with the epitaxial layer, has been included. The analytical solution was verified with numerical simulations based on parameters extracted from a standard 0.35 µm CMOS process. Two empirical parameters are suggested to offset the unavoidable inaccuracies in the extracted parameter values. The derived semi-empirical expression exhibits a good agreement with the measured spectral response. The lateral photoresponse in CMOS photodiode arrays is investigated with test linear photodiode arrays and numerical device simulations. It is shown that the surface recombination and mobility degradation along the Si-SiO 2 interface are important factors in determining the lateral photoresponse of CMOS photodiodes. The limitations of traditional analytical approaches are briefly discussed in this context, and a novel three-dimensional analysis of lateral photoresponse is presented. Given the significant dependence of lateral photoresponse on the Si-SiO 2 interface quality, an empirical characterization method is proposed as a more reliable solution to modeling lateral photoresponse. Lateral crosstalk in CMOS imaging array deter effective utilization of small pixel sizes (e.g. < 5.0 µm x 5.0 µm) now permitted by technology scaling. …