Initial results from a cryogenic proton irradiation of a p-channel CCD

Abstract-P-channel CCDs have been shown to display improved tolerance to radiation-induced charge transfer inefficiency (CTI) when compared to n-channel CCDs. This is attributed to the properties of the dominant charge-trapping defect species in p-channel silicon relative to the operating conditions of the CCD. However, precise knowledge of defect parameters is required in order to correct for any induced CTI. The method of single trap-pumping allows us to analyse the defect parameters to a degree of accuracy that cannot be achieved with other common defect analysis techniques such as deep-level transient spectroscopy (DLTS). We have analysed using this method the defect distribution in an e2v p-channel CCD204 irradiated with protons at cryogenic temperature (153K). The dominant charge trapping defects at these conditions have been identified as the donor level of the silicon divacancy and the carbon interstitial defect. The defect parameters are analysed both immediately post irradiation and following several subsequent room-temperature anneal phases. The evolution of the defect distribution over time and through each anneal phase provides insight into defect interactions and mobility post-irradiation. The results demonstrate the importance of cryogenic irradiation and annealing studies, with large variations seen in the defect distribution when compared to a device irradiated at room-temperature, which is the current standard procedure for radiation testing.

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“…For this study two CCD204 devices were irradiated at the Synergy Health 5MV Tandem Accelerator (UK) [11].…”

Section: Trap Pumpingmentioning

confidence: 99%

Evolution of proton-induced defects in a cryogenically irradiated p-channel CCD

Wood

Hall

Gow

et al. 2016

2016 16th European Conference on Radiation and Its Effects on Components and Systems (RADECS)

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“…Typically a proton irradiation performed to investigate post-irradiation performance for a space mission is performed at room temperature, however, based on the evidence from other studies looking into the performance of devices irradiated at cryogenic temperatures 3,[6][7][8][9][10][11][12][15][16][17] , this may not provide the conditions to allow appropriate minimisation of radiation induced CTI. This is because of the mobility of individual defects after the irradiation and their ability to interact with other defects to form different defects.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, immediately there is less concentration of impurities from which stable defects can be formed that could impact charge transfer. The radiation induced defects which increase Charge Transfer Inefficiency (CTI) in a p-channel CCD have been linked to the divacancy and other traps related to carbon and oxygen interstitials [4][5][6][7][8][11][12] . As there are less radiation induced defects in a p-channel CCD which have been shown to increase CTI and because they are formed in smaller quantities (the divacancy is a second order defect and boron defects have not been shown to impact CTE) when compared to an n-channel equivalent, p-channel CCDs are more hard to radiation induced CTI.…”

Section: Introductionmentioning

confidence: 99%

“…The study described in this paper was performed as part of a European Space Agency (ESA) funded investigation (TEC-MME/2012/298) into the performance benefits provided through the use of a p-channel rather than an n-channel CCD [10][11][12] . The overall aim of the study was to build upon our understanding of device behaviour and the impact of performing irradiations at cryogenic temperatures and how the observed defect concentrations linked to CTI measurements.…”

Section: Introductionmentioning

confidence: 99%

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Charge transfer efficiency in a p-channel CCD irradiated cryogenically and the impact of room temperature annealing

et al. 2016

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It is important to understand the impact of the space radiation environment on detector performance, thereby ensuring that the optimal operating conditions are selected for use in flight. The best way to achieve this is by irradiating the device using appropriate mission operating conditions, i.e. holding the device at mission operating temperature with the device powered and clocking. This paper describes the Charge Transfer Efficiency (CTE) measurements made using an e2v technologies p-channel CCD204 irradiated using protons to the 10 MeV equivalent fluence of 1.24×10 9 protons.cm -2at 153 K. The device was held at 153 K for a period of 7 days after the irradiation before being allowed up to room temperature where it was held at rest, i.e. unbiased, for twenty six hours to anneal before being cooled back to 153 K for further testing, this was followed by a further one week and three weeks of room temperature annealing each separated by further testing. A comparison to results from a previous room temperature irradiation of an n-channel CCD204 is made using assumptions of a factor of two worse CTE when irradiated under cryogenic conditions which indicate that p-channel CCDs offer improved tolerance to radiation damage when irradiated under cryogenic conditions.

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“…Perhaps even more useful is the ability to track traps from irradiation, through annealing and further transitions in the device. Different irradiation conditions can be studied in intense detail and the impact and importance of cryogenic irradiations has been strongly demonstrated [21][22][23]. The technique is being used as a tool to understand the impact of radiation damage on CCDs for future mission studies, such as in the low-signal regime for WFIRST [24][25][26][27].…”

Section: Introductionmentioning

confidence: 99%

Mapping radiation-induced defects in CCDs through space and time

et al. 2016

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The Charge Coupled Device (CCD) has long been the detector of choice for many space-based applications. The CCD converts the signal X-rays or visible light into electrons (n-channel devices) or holes (p-channel devices) which are stored in the pixel structure during integration until the subsequent transfer of the charge packets through the device to be read out. The transfer of this signal charge is, however, not a perfect process.Throughout the lifetime of a space-based mission the detector will be bombarded by high-energy particles and gamma rays. As time progresses, the radiation will damage the detectors, causing the Charge Transfer Efficiency (CTE) to decrease due to the creation of defects or "traps" in the silicon lattice of the detector. The defects create additional energy levels between the valence and conduction band in the silicon of the detector. Electrons or holes (for n-channel or pchannel devices respectively) that pass over the defect sites may be trapped. The trapped electrons or holes will later be emitted from the traps, subject to an emission-time constant related to the energy level of the associated defect. The capture and emission of charge from the signal leads to a characteristic trailing or "smearing" of images that must be corrected to enable the science goals of a mission to be met.Over the past few years, great strides have been taken in the development of the pocket-pumping (or strictly-speaking "trap pumping") technique. This technique not only allows individual defects (or traps) within the device to be located to the sub-pixel level, but it enables the investigation of the trap parameters such as the emission time constant to new levels of accuracy. Recent publications have shown the power of this technique in characterising a variety of different defects in both n-and p-channel devices and the potential for use in correction techniques, however, we are now exploring not only the trap locations and properties but the life cycle of these traps through time after irradiation. In orbit, most devices will be operating cold to suppress dark current and the devices are therefore cold whilst undergoing damage from the radiation environment. The mobility of defects varies as a function of temperature such that the mix of defects present following a cryogenic irradiation may vary significantly from that found following a room temperature irradiation or after annealing. It is therefore essential to study the trap formation and migration in orbit-like conditions and over longer timescales.In this paper we present a selection of the latest methods and results in the trap pumping of n-and p-channel devices and demonstrate how this technique now allows us to map radiation-induced defects in CCDs through both space and time.

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Initial results from a cryogenic proton irradiation of a p-channel CCD

Cited by 5 publications

References 20 publications

Evolution of proton-induced defects in a cryogenically irradiated p-channel CCD

Evolution of proton-induced defects in a cryogenically irradiated p-channel CCD

Charge transfer efficiency in a p-channel CCD irradiated cryogenically and the impact of room temperature annealing

Mapping radiation-induced defects in CCDs through space and time

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