Temperature dependence and dynamic behaviour of full well capacity in pinned photodiode CMOS image sensors

Abstract

This study 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 take into account 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 study also shows that after a light pulse, the charge stored in the PPD drops as the PPD tends toward equilibrium. On the base of these observations, an analytical model of the dynamic behaviour of the FWC in non-continuous 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.