Design, Fabrication, and Modeling of CMOS-Compatible Double Photodiode

A double photodiode (PD) constructed by p?/Nwell junction and N-well/p-sub junction was designed and fabricated in a UMC 0.18-lm CMOS process. Based on the device structure and mechanism of double PD, a novel small-signal equivalent circuit model considering the carrier transit effect and the parasitic RC time constant was presented. By this model with complete electronic components,the double PD can be incorporated in a commercial circuit simulator. The component values were extracted by fitting the measured S-parameters using simulated annealing algorithm, and a good agreement between the measurement and the simulation results was achieved.