Proton irradiation of a swept charge device at cryogenic temperature and the subsequent annealing

A number of studies have demonstrated that a room temperature proton irradiation may not be sufficient to provide an accurate estimation of the impact of the space radiation environment on detector performance. This is a result of the relationship between defect mobility and temperature, causing the performance to vary subject to the temperature history of the device from the point at which it was irradiated. Results measured using Charge Coupled Devices (CCD) irradiated at room temperature therefore tend to differ from those taken when the device was irradiated at a cryogenic temperature, more appropriate considering the operating conditions in space, impacting the prediction of in-flight performance. This paper describes the cryogenic irradiation, and subsequent annealing of an e2v technologies Swept Charge Device (SCD) CCD236 irradiated at −35.4°C with a 10 MeV equivalent proton fluence of 5.0 × 108 protons centerdot cm−2. The CCD236 is a large area (4.4 cm2) X-ray detector that will be flown on-board the Chandrayaan-2 and Hard X-ray Modulation Telescope spacecraft, in the Chandrayaan-2 Large Area Soft X-ray Spectrometer and the Soft X-ray Detector respectively. The SCD is readout continually in order to benefit from intrinsic dither mode clocking, leading to suppression of the surface component of the dark current and allowing the detector to be operated at warmer temperatures than a conventional CCD. The SCD is therefore an excellent choice to test and demonstrate the variation in the impact of irradiation at cryogenic temperatures in comparison to a more typical room temperature irradiation

Proton radiation damage study of the next generation of swept charge devices

The first generation of Swept Charge Device (SCD) the e2v technologies plc CCD54 was used in the Demonstration of a Compact Imaging X-ray Spectrometer (D-CIXS) launched in 2003 and again in the Chandrayaan-1 X-ray Spectrometer (C1XS) instrument currently in orbit around the Moon. The main source of decreased energy resolution in both cases is proton damage, from trapped and solar protons respectively. This paper presents the results from an experimental study to evaluate the performance of the next generation of SCD the CCD234 and CCD236 irradiated with a 10 MeV equivalent proton fluence of 3.0?108 protons.cm-2, demonstrating the factor of two increase in radiation hardness when compared to the CCD54. In particular the increased dark current, decrease in energy resolution and the degradation of charge transfer efficiency (CTE) are described

Importance of charge capture in interphase regions during readout of charge-coupled devices

The current understanding of charge transfer dynamics in charge-coupled devices (CCDs) is that charge is moved so quickly from one phase to the next in a clocking sequence and with a density so low that trapping of charge in the interphase regions is negligible. However, simulation capabilities developed at the Centre for Electronic Imaging, which includes direct input of electron density simulations, have made it possible to investigate this assumption further. As part of the radiation testing campaign of the Euclid CCD273 devices, data have been obtained using the trap pumping method, a method that can be used to identify and characterize single defects within CCDs. Combining these data with simulations, we find that trapping during the transfer of charge among phases is indeed necessary to explain the results of the data analysis. This result could influence not only trap pumping theory and how trap pumping should be performed but also how a radiation-damaged CCD is readout in the most optimal way

Metabolism impacts upon Candida immunogenicity and pathogenicity at multiple levels

Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved. Open Access funded by Wellcome TrustNon peer reviewedPublisher PD

A study of the double-acceptor level of the silicon divacancy in a proton irradiated n-channel CCD

Radiation damage effects are problematic for space-based detectors. Highly energetic particles, predominantly from the sun can damage a detector and reduce its operational lifetime. For an image sensor such as a Charge-Coupled Device (CCD) impinging particles can potentially displace silicon atoms from the CCD lattice, creating defects which can trap signal charge and degrade an image through smearing. This paper presents a study of one energy level of the silicon divacancy defect using the technique of single trap-pumping on a proton irradiated n-channel CCD. The technique allows for the study of individual defects at a sub-pixel level, providing highly accurate data on defect parameters. Of particular importance when concerned with CCD performance is the emission time-constant of a defect level, which is the time-scale for which it can trap a signal charge. The trap-pumping technique is a direct probe of individual defect emission time-constants in a CCD, allowing for them to be studied with greater precision than possible with other defect analysis techniques such as deep-level transient spectroscopy on representative materials

Postirradiation behavior of p-channel charge-coupled devices irradiated at 153 K

The displacement damage hardness that can be achieved using p-channel charge-coupled devices (CCD) was originally demonstrated in 1997, and since then a number of other studies have demonstrated an improved tolerance to radiation-induced CTI when compared to n-channel CCDs. A number of recent studies have also shown that the temperature history of the device after the irradiation impacts the performance of the detector, linked to the mobility of defects at different temperatures. This study describes the initial results from an e2v technologies p-channel CCD204 irradiated at 153 K with a 10 MeV equivalent proton fluences of 1.24×109 and 1.24×1011 protons cm-2. The dark current, cosmetic quality and the number of defects identified using trap pumping immediately were monitored after the irradiation for a period of 150 hours with the device held at 153 K and then after different periods of time at room temperature. The device also exhibited a flatband voltage shift of around 30 mV / krad, determined by the reduction in full well capacity

A comparative study of proton radiation damage in p- and n-channel

It has been demonstrated that p-channel charge coupled devices (CCDs) are more radiation hard than conventional n-channel devices as they are not affected by the dominant electron trapping caused by the displacement damage defect the E-centre (phosphorus-vacancy). This paper presents a summary of the results from a comparative study of n-channel and p-channel CCDs each type operated under the same conditions. The CCD tested is the e2v technologies plc CCD47-20, a 1024 ? 1024 frame transfer device with a split output register, fabricated using the same mask to form n-channel and p-channel devices. The p-channel devices were irradiated to a 10 MeV equivalent proton fluence of 4.07?1010 protons.cm-2 and 1.35?1011 protons.cm-2, an n-channel CCD was irradiated to a 10 MeV equivalent proton fluence of 1.68?109 protons.cm-2, however due to time constraints the n-channel device was not characterised, n-channel comparisons are instead made using a CCD02. As expected the p-channel CCD demonstrated improved radiation tolerance when compared to the n-channel CCD, at -90 ?C there is an approximate ×7 and ×15 improvement in tolerance to radiation induced parallel and serial CTI respectively for equivalent pixel geometries

Co-transport-induced instability of membrane voltage in tip-growing cells

A salient feature of stationary patterns in tip-growing cells is the key role played by the symports and antiports, membrane proteins that translocate two ionic species at the same time. It is shown that these co-transporters destabilize generically the membrane voltage if the two translocated ions diffuse differently and carry a charge of opposite (same) sign for symports (antiports). Orders of magnitude obtained for the time and lengthscale are in agreement with experiments. A weakly nonlinear analysis characterizes the bifurcation

The X-ray quantum efficiency measurement of high resistivity CCDs

The CCD247 is the second generation of high-resistivity device to be manufactured in e2v technologies plc development programme. Intended for infrared astronomy, the latest devices are fabricated on high resistivity (~8 kΩ cm) bulk silicon, allowing for a greater device thickness whilst maintaining full depletion when 'thinned' to a thickness of 150 μm. In the case of the front illuminated variant, depletion of up to 300 μm is achievable by applying a gate to substrate potential of up to 120 V, whilst retaining adequate spectral performance. The increased depletion depth of high-resistivity CCDs greatly improves the quantum efficiency (QE) for incident X-ray photons of energies above 5 keV, making such a device beneficial in future X-ray astronomy missions and other applications. Here we describe the experimental setup and present results of X-ray QE measurements taken in the energy range 2-20 keV for a front illuminated CCD247, showing QE in excess of 80% at 10 keV. Results for the first generation CCD217 and swept-charge device (1500 Ω cm epitaxial silicon) are also presented

Cell wall protection by the Candida albicans class I chitin synthases

Open Access funded by Medical Research Council Acknowledgments We thank Kevin Mackenzie in the Microscopy and Histology Core Facility (Institute of Medical Sciences, University of Aberdeen), and Donna MacCallum for helpful statistical advice. This work was supported by grants from the Wellcome Trust (0868827 and 080088) including a Wellcome Trust Strategic Award (097377) and an Investigator Award to NG (101873), an MRC New Investigator Award to ML (MR/J008230/1) and a PhD scholarship awarded to KP from the Ministry of Sciences and Technology and Chiang Mai University, Thailand. Author contributions are as follows: KP constructed strains, performed the majority of the experiments, analyzed the data and contributed to the preparation of the manuscript. JA produced Fig. S1 using the data from the phosphoproteomic analysis conducted by SP and AB. NG conceived and designed experiments, analyzed data and commented on drafts of the manuscript. ML constructed strains, conceived, designed and performed experiments, analyzed data and wrote the manuscript.Peer reviewedPublisher PD