A New Analytical Pinned Photodiode Capacitance Model

A new mathematical model is proposed for the capacitance of the pinned photodiode (PPD) taking into account the potential changes at the PPD center. Aside from the electric field and the depletion region that is created by the p-n junctions, a depletion process occurs at the center of PPD. In this letter, the total capacitance of PPD is demonstrated to be composed of two series capacitances; the junction capacitance around the PPD and the inner capacitance at the PPD center. For the junction capacitance calculation, a previously developed model can be utilized. On the other hand, the inner capacitance is a result of the depletion at the PPD center, which is modeled in this letter. Both capacitances are voltage-dependent and the total series capacitance fits to the measurement data.