Study of the behavior of commercial CCDs images sensors in a space environment

We studied the behavior of CCD images sensors exposed to a spatial radiative constraint. The aim of this work is to compare the degradation of the sensitive parameters between commercial components and hardened ones. It appears that the dark current density of commercial CCDs is sensitive to total dose. This parameter is the main source of degradation for dose levels up to 200 Gy(Si). The induced oxide charge is the prime responsible for this behavior as shown by the partial annealing of the dark current under 100 C heating. It is shown that this charge deposited in isolation oxides induces an inversion zone at the semiconductor surface leading to the creation of a parasitic transistor. Numerical simulations show the thermal activation of the leakage currents due to this structure, and confirm the experimental observations. The irradiation of CCD with particles generating bulk defaults like protons and neutrons leads to the observation of a dark current increase induced by the contribution of elastic (for protons) and inelastic interactions between incident particles and semiconductor atoms. The associated total dose deposition (proton) provides an additional contribution to the mean degradation. The occurrence of pixels with a large RTS and the increase of the charge transfer inefficiency (CTI) can also be noticed. In a hardness assurance context, this work provides a better understanding of the critical points, which have to be taken into account in order to propose a good estimation of the CCD degradation for a spatial application. We should keep in mind the predominant role of leakage currents that directly affect the measurement of the conversion factor or the CTI. This behavior differs from the one observed with hardened CCDs. The characterization of commercial sensors under total dose is proving to be mandatory, as well as the estimation of the number of pixels with a large dark current and the probability of RTS occurrence in case of non ionising effects. (author)