Fig. 1.
Illustration of a 4T pixel with a PPD structure. (a) 4T pixel circuit schematic. (b) Electrical crosstalk mechanism between neighboring PPDs.
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Chen Cao, Bing Zhang, Xin Li, Longsheng Wu, Junfeng Wang. Photoelectric characteristics of an inverse U-shape buried doping design for crosstalk suppression in pinned photodiodes[J]. Journal of Semiconductors, 2014, 35(11): 114009. doi: 10.1088/1674-4926/35/11/114009
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C Cao, B Zhang, X Li, L S Wu, J F Wang. Photoelectric characteristics of an inverse U-shape buried doping design for crosstalk suppression in pinned photodiodes[J]. J. Semicond., 2014, 35(11): 114009. doi: 10.1088/1674-4926/35/11/114009.
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Photoelectric characteristics of an inverse U-shape buried doping design for crosstalk suppression in pinned photodiodes
DOI: 10.1088/1674-4926/35/11/114009
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Abstract
A design of an inverse U-shape buried doping in a pinned photodiode (PPD) of CMOS image sensors is proposed for electrical crosstalk suppression between adjacent pixels. The architecture achieves no extra fill factor consumption, and proper built-in electric fields can be established according to the doping gradient created by the injections of the extremely low P-type doping buried regions in the epitaxial layer, causing the excess electrons to easily drift back to the photosensitive area rarely with a diffusion probability; the overall junction capacitance and photosensitive area extensions for a full well capacity (FWC) and internal quantum efficiency (IQE) improving are achieved by the injection of a buried N-type doping. By considering the image lag issue, the process parameters of all the injections have been precisely optimized. Optical simulation results based on the finite difference time domain method show that compared to the conventional PPD, the electrical crosstalk rate of the proposed architecture can be decreased by 60%-80% at an incident wavelength beyond 450 nm, IQE can be clearly improved at an incident wavelength between 400 and 600 nm, and the FWC can be enhanced by 107.5%. Furthermore, the image lag performance is sustained to a perfect low level. The present study provides important guidance on the design of ultra high resolution image sensors. -
References
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