Random telegraph dark signal fluctuations have been studied in two types of CCD and two types of CMOS active pixel sensor after proton irradiation at 1.5, 10 and 60 MeV. Time constants and activation energies were very similar, indicating a similar defect type. A large fraction of the defects are multi-rather than 2-level, suggest ing a mechanism related to defect clusters being formed from initial single proton events.
A STARIOOO CMOS active pixel sensor was irradiated with alpha particles at -130°C and dark current measurements were made at tern peratures up to 25°C. Approximately 90% of dark current spikes were seen to anneal near room tern perature. This im plies that room tern perature irradiations will not give a good estimate of on-orbit effects for cooled applications.
This paper reports on the radiation response of 90 nm CMOS transistors to a high fluence (3x1012 p/cm2) of -60 MeV protons. A pronounced dependence on the gate bias VGS during the exposure has been noted for the n-channel devices: while no degradation of the input and output characteristics is found for VGS=O V and a modest degradation for floating gate conditions, a catastrophic failure can be observed when a positive gate bias of 1.2 V is applied. This behaviour is found for devices with a physical gate oxide thickness of 1.5 and 2 nm and appears to be more pronounced for larger area transistors. As will be shown, the breakdown site is connected with either the source-to-gate or drain-to-gate junction, whereby the latter leads to a complete loss of functionality of the transistors. However, some of the biased n-MOSFETs survive the highenergy proton exposure without degradation. A model will be proposed, explaining the gate oxide breakdown in terms of a synergy between gate current flow and proton irradiation.
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