MOS-based model of four-transistor CMOS image sensor pixels for photoelectric simulation |
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| Affiliation: | 1.School of Microelectronics, Xi'an Jiaotong University, Xi'an 710049, China;2.Key Laboratory of Micro-nano Electronics and System Integration of Xi'an City, Xi'an 710049, China;3.National Key Laboratory of Science and Technology on Micro/Nano Fabrication, Peking University, Beijing 100871, China;4.ABAX Sensing Inc., Ningbo 315500, China |
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| Abstract: | By using the MOS-based model established in this paper, the physical process of photoelectron generation, transfer, and storage in the four-transistor active pixel sensor (4T-APS) pixels can be simulated in SPICE environment. The variable capacitance characteristics of double junctions in pinned photodiodes (PPDs) and the threshold voltage difference formed by channel nonuniform doping in transfer gates (TGs) are considered with this model. The charge transfer process of photogenerated electrons from PPDs to the floating diffusion (FD) is analyzed, and the function of nonuniform doping of TGs in suppressing charge injection back to PPDs is represented with the model. The optical and electrical characteristics of all devices in the pixel are effectively combined with the model. Moreover, the charge transfer efficiency and the voltage variation in PPD can be described with the model. Compared with the hybrid simulation in TCAD and the Verilog-A simulation in SPICE, this model has higher simulation efficiency and accuracy, respectively. The effectiveness of the MOS-based model is experimentally verified in a 3 μ m test pixel designed in 0.11 μm CIS process. |
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| Keywords: | four-transistor active pixel sensor (4T-APS) nonuniform doping SPICE model transfer gate variable capacitance |
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