The current trend toward image sensors with ever-increasing pixel counts is prompting continual reductions in pixel area, leading to significant cross-talk and efficiency challenges. The realization of image sensor pixels containing waveguides presents a means for addressing these issues. The fabrication of such pixels is however not straightforward. Conventional waveguides employed in integrated optics are horizontal, but waveguides needed for the proposed sensor must be vertical and integrated with photodetectors. Here, the authors describe a fabrication process for vertical silicon nitride waveguides integrated with silicon photodetectors. The authors describe the etching, deposition, and planarization techniques that enable the formation of silicon nitride waveguides embedded in silicon dioxide. They also describe a fabrication process for silicon photodetectors, including a means for ensuring that their photosensitive areas have sizes consistent with those of photodetectors employed in conventional image sensors. In addition, the authors perform optical and electrical characterization of the fabricated devices. The results demonstrate the ability of the fabricated waveguides to guide light onto the photodetectors with high efficiency.

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Journal Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures
Tut, T. (Turgut), Dan, Y. (Yaping), Duane, P. (Peter), Ye, W.N, Degirmenci, F. (Fatih), Yu, Y. (Young), … Crozier, K.B. (Kenneth B.). (2014). Silicon photodetectors integrated with vertical silicon nitride waveguides as image sensor pixels: Fabrication and characterization. Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures, 32(3). doi:10.1116/1.4868627