Towards a SPR-based biosensing platform incorporating a CMOS active column sensor
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A biosensing platform based on surface plasmon resonance and incorporating a CMOS imager is being developed. This work comprises three different tasks towards this goal: a numerical analysis to determine the optimal plasmon resonance conditions, a numerical analysis to select the best CMOS photodiode and the architecture proposal of a CMOS imager. A simulation with COMSOL of a Kretschmann configuration using CMOS/post-CMOS compatible materials, a silicon dioxide prism and a gold-water interface, showed an optimal metal thickness of 50 nm and the associated incidence resonance angle of 68.46. Then, a simulation with Silvaco ATLAS of two different CMOS photodiodes, a n-diff/p-sub and a n-well/p-sub, showed that the latter has a maximum quantum efficiency of 82 % and a photcurrent of 85 nA at 633 nm. This photodiode was selected as the photosensing element in a 20 × 20 ¿m2 pixel with a 61 % fill factor. A 32 × 32-pixel CMOS active column sensor (ACS) with fixed pattern noise (FPN) reduction was proposed. It includes non-correlated double sampling and double delta sampling schemes for noise handling. The reduction of the output's variance was demonstrated through Monte Carlo analysis. An experimental optical setup was used to characterize the performance of the imager, obtaining a conversion gain of 7.3 ¿V/e- and a photodiode capacitance of 22 fF, showing good agreement with the values obtained with electrical simulation of 5.2 ¿V/e- and 31 fF. The measured full-well saturation was of 118.8 × 103 e- or 2.4 V. Finally, pixel-FPN and column-FPN of 0.09 and 0.06 % respectively were obtained. The low FPN levels demonstrate the benefits of the ACS and noise reduction circuits implemented. This work provide valuable information for the upcoming implementation of an integrated SPR-biosensing platform incorporating a CMOS-ACS. © 2013 Springer Science+Business Media New York.