A method to extract the pinned photodiode (PPD) physical parameters inside a CMOS image sensor pixel array is presented. The proposed technique is based on the Tan et al. pinning voltage characteristic. This pixel device characterization can be performed directly at the solid-state circuit output without the need of any external test structure. The presented study analyzes the different injection mechanisms involved in the different regimes of the characteristic. It is demonstrated that in addition to the pinning voltage, this fast measurement can be used to retrieve the PPD capacitance, the pixel equilibrium full well capacity, and both the transfer gate threshold voltage and its channel potential at a given gate voltage. An alternative approach is also proposed to extract an objective pinning voltage value from this measurement.

International audienceThis letter presents a simple analytical model for the evaluation of the full well capacity (FWC) of pinned photodiode (PPD) CMOS image sensors depending on the operating conditions and on the pixel parameters. While in the literature and technical documentations FWC values are generally presented as fixed values independent of the operating conditions, this letter demonstrates that the PPD charge handling capability is strongly dependent on the photon flux

This paper presents an analytical model of the full well capacity (FWC) in pinned photodiode (PPD) CMOS image sensors. By introducing the temperature dependence of the PPD pinning voltage, the existing model is extended (with respect to previous works) to consider the effect of temperature on the FWC. It is shown, with the support of experimental data, that whereas in dark conditions the FWC increases with temperature, a decrease is observed if FWC measurements are performed under illumination. This paper also shows that after a light pulse, the charge stored in the PPD drops as the PPD tends toward equilibrium. On the basis of these observations, an analytical model of the dynamic behavior of the FWC in noncontinuous illumination conditions is proposed. The model is able to reproduce experimental data over six orders of magnitude of time. Both the static and dynamic models can be useful tools to correctly interpret FWC changes following design variations and to accurately define the operating conditions during device characterizations.Index Terms-Active pixel sensor (APS), analytical modeling, capacitance, CMOS image sensor (CIS), dynamic behavior, full well capacity (FWC), modeling, pinned photodiode (PPD), pinning voltage, temperature.