Gordon R. Hopkinson

Radiation effects in a CMOS active pixel sensor

A CMOS active pixel sensor has been evaluated with Co60, 10 MeV proton and heavy-ion irradiation. Permanent displacement damage effects were seen but total ionizing dose-induced dark current and increase in power supply current annealed at 100/spl deg/C. Large changes in responsivity were seen after proton irradiation, which subsequently annealed. Mechanisms for these responsivity changes are discussed, but a definitive cause has not yet been established.

Radiation effects on photonic imagers-a historical perspective

Photonic imagers are being increasingly used in space systems, where they are exposed to the space radiation environment. Unique properties of these devices require special considerations for radiation effects. This paper summarizes the evolution of radiation effects understanding in infrared detector technology, charge coupled devices, and active pixel sensors. The paper provides a discussion of key radiation effects developments and a view of the future of the technologies from a radiation effects perspective.

Multilevel RTS in Proton Irradiated CMOS Image Sensors Manufactured in a Deep Submicron Technology

A new automated method able to detect multilevel random telegraph signals (RTS) in pixel arrays and to extract their main characteristics is presented. The proposed method is applied to several proton irradiated pixel arrays manufactured using a 0.18 mum CMOS process dedicated to imaging. Despite the large proton energy range and the large fluence range used, similar exponential RTS amplitude distributions are observed. A mean maximum amplitude independent of displacement damage dose is extracted from these distributions and the number of RTS defects appears to scale well with total nonionizing energy loss. These conclusions allow the prediction of RTS amplitude distributions. The effect of electric field on RTS amplitude is also studied and no significant relation between applied bias and RTS amplitude is observed.

Radiation effects on a radiation-tolerant CMOS active pixel sensor

A comprehensive cobalt60, proton, and heavy ion evaluation of the Fillfactory STAR-250 CMOS active pixel sensor has been performed for space applications up to 100 krd(Si). It was possible to eliminate image lag by adjustment of the bias voltage and this allowed a reduction in proton-induced dark signal. Both cobalt60 and proton irradiation produced a decrease in responsivity, which is thought to be due to total dose effects. There was also an increase in photoresponse nonuniformity (PRNU). No major single event effects (latch-up or functional interrupt) where seen at the maximum linear energy transfer (LET) of 68MeV/(mg/cm/sup 2/).

Radiation effects on astrometric CCDs at low operating temperatures

Emission times of proton-induced traps and optical spot profiles have been measured at temperatures around -110/spl deg/C for large format charge-coupled devices (CCDs), representative of those to be used for the Gaia mission. There are at least seven trap species involved, with emission times in the range 0.3 /spl mu/s to 130 s and there is evidence for charge re-trapping by fast traps. Trap filling using a charge injection gate is discussed.

Comparison of CCD damage due to 10- and 60-MeV protons

Dark current and charge transfer inefficiency (CTI) data are presented for three charge-coupled devices (CCD) device types after 9.5- and 60-MeV proton irradiation. Comparison of the damage at the two energies allows a test of the validity of NIEL scaling. The ratio of the damage at 9.5 MeV to that at 60 MeV was found to be 35% higher for the CTI than for the average bulk dark current, for the devices tested. Both the CTI and the dark current showed significant annealing at 150/spl deg/C, and this has implications for the lattice defects involved. Cobalt-60 data are also discussed.

Random Telegraph Signals in Proton Irradiated CCDs and APS

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, suggesting a mechanism related to defect clusters being formed from initial single proton events.

Proton-induced changes in CTE for n-channel CCDs and the effect on star tracker performance

Proton-induced changes in charge transfer efficiency of two CCD types with differing pixel sizes have been characterized in detail and compared with measurements of the shift in position of artificial star images to determine the impact on star tracker performance. Errors in star position are large at low backgrounds but can be limited to less than 0.1 pixels for 10 krd(Si) proton environments (e.g., 15 years GEO) if the background is high and windowed readout is used.

Effects of Low Temperature Proton Irradiation on a Large Area CCD for Astrometric Applications

Charge transfer and dark current effects are compared for regions of a large area 4500 × 1966 pixel CCD irradiated with 7.4 MeV protons at -130°C and at room temperature. Post-annealing measurements were also performed. Although there are differences in the concentration of individual defects following warm and -130°C irradiation and after subsequent annealing steps, these differences were less than a factor 3.5 (and in most cases a factor 2)-with the room temperature irradiation giving a good estimate of the effects except for traps with emission time constant ~4 ms.

Proton-induced CCD charge transfer degradation at low-operating temperatures

Measurements of charge transfer inefficiency (CTI) at charge-coupled device temperatures /spl sim/-100/spl deg/C show that proton-induced E-centers can be kept filled but other traps with energies 0.22-0.34 eV limit the achievable improvement in CTI. Estimates of trap energy levels and concentrations are made from CTI and emission time measurements. It is found that the CTI can be reduced for low signal levels. Implications for spaceborne astronomical instruments are discussed.