Device modelling and model verification for the Euclid CCD273 detector

Euclid is one of the M-class missions selected for the next phase of ESA’s long-term Cosmic Vision programme. The primary goal of this mission is to observe the distribution and shapes of distant galaxies, with the aim of mapping and characterising the dark energy which makes up about 70% of the universe. This will be achieved by measuring the effects of weak lensing on the captured images, in terms of the distortion caused to the elipticity of galaxy shapes [1]. The e2v CCD273 was designed for the Euclid mission and is adapted from an older design (the CCD203) with changes made to improve CTE under irradiation by solar protons. Reducing the effects of radiation damage in the image sensor will result in images which have minimal distortion. This paper is focused on the on-going development and verification of 3D device models and their integration with Monte Carlo radiation damage models. Parameters such as charge interaction volume versus signal size, pixel full well capacity, and charge transfer behaviour for both the parallel and serial registers will be discussed. The main mission goals are aimed at measuring distortion due to weak lensing, so it is important to differentiate this from distortion due to radiation damage. This work will eventually lead to a method of post processing images to remove the effects of radiation damage

Pixel-level modelling and verification for the EUCLID VIS CCD

Euclid is an M-class mission selected for the next phase of ESA’s long-term Cosmic Vision programme. The mission’s primary aim is to provide insight into the physical cause of the accelerating universe which will be achieved by investigating the nature of dark energy, dark matter and gravity. The investigation will involve the measurement of the effects of intervening gravitational potentials on visible light from distant galaxies, a process known as weak gravitational lensing. The CCD273 was designed by e2v for the Euclid mission, and is based on an older design for the CCD204, with changes designed and implemented to improve operation under irradiation. These changes include a narrower buried channel in the serial register to reduce trap interactions during readout. Pixel level models have been developed to improve knowledge of charge packet distribution within the CCD273 and CCD204 using Silvaco TCAD, enabling more effective predictions to be made about device functionality before and after irradiation which can be immediately tested on both devices. This paper is focussed on latest results, with particular reference to the on-going model verification, designed to build confidence in the device models and provide feedback to further improve the modelling effort

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

Influence of Habitat and Number of Nestlings on Partial Brood Loss in Red-Cockaded Woodpeckers

Partial brood loss in red-cockaded woodpeckers (Picoides borealis) was studied during 2 breeding seasons in eastern Texas. The timing of partial brood loss, group size, number of initial nestlings, number of birds fledged, and habitat characteristics of the group\u27s cavity-tree cluster were examined for 37 woodpecker groups in loblolly- (Pinus taeda) shortleaf (P. echinata) pine habitat and 14 groups in longleaf (P palustris) pine habitat. Partial brood loss occurred slightly more in the loblolly-shortleaf pine habitat than in the longleaf pine habitat, largely because nests in loblolly-shortleaf habitat initially contained more nestlings. There was a trend for more young to be fledged by groups of 4 and 5 adult woodpeckers than by groups with only 2 or 3 adult birds. Partial brood loss was greater in nests with 4 initial nestlings than in nests with 3 or fewer nestlings. Partial brood loss was always observed in nests that initially contained 4 nestlings. When nests contained 3 nestlings, partial brood loss was significantly greater in clusters where hardwood midstory was present than in clusters where hardwood midstory was minimal, consistent with the brood reduction theory. Red-cockaded woodpeckers typically laid more eggs than they could possibly fledge young, lending support to the insurance egg hypothesis

An ion ring in a linear multipole trap for optical frequency metrology

A ring crystal of ions trapped in a linear multipole trap is studied as a basis for an optical frequency standard. The equilibrium conditions and cooling possibilities are discussed through an analytical model and molecular dynamics simulations. A configuration which reduces the frequency sensitivity to the fluctuations of the number of trapped ions is proposed. The systematic shifts for the electric quadrupole transition of calcium ions are evaluated for this ring configuration. This study shows that a ring of 10 or 20 ions allows to reach a short term stability better than for a single ion without introducing limiting long term fluctuations

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

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 number of defects identified using trap pumping, dark current and cosmetic quality immediately after irradiation and over a period of 150 hours after the irradiation with the device held at 153 K and then after different periods of time at room temperature are described. The device also exhibited a flatband voltage shift of around 30 mV per krad, determined by the reduction in full well capacity

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

Social Cohesion, Structural Holes, and a Tale of Two Measures

EMBARGOED - author can archive pre-print or post-print on any open access repository after 12 months from publication. Publication date is May 2013 so embargoed until May 2014.This is an author’s accepted manuscript (deposited at arXiv arXiv:1211.0719v2 [physics.soc-ph] ), which was subsequently published in Journal of Statistical Physics May 2013, Volume 151, Issue 3-4, pp 745-764. The final publication is available at link.springer.com http://link.springer.com/article/10.1007/s10955-013-0722-

Assessment of proton radiation-induced charge transfer inefficiency in the CCD273 detector for the Euclid Dark Energy Mission

Euclid is a medium class mission selected for launch in 2019, with a primary goal to study the dark universe using the weak lensing and baryonic acoustic oscillations techniques. Weak lensing depends on accurate shape measurements, therefore it is beneficial that the effects of radiation-induced charge transfer inefficiency (CTI) in the Euclid CCD over the six year mission are understood and minimised. This paper describes the initial evaluation of the tolerance to radiation induced charge transfer inefficiency (CTI) of the CCD273 produced by e2v technologies plc, making comparisons with the previous CCD selected for Euclid the CCD203. The CCD273 benefits from the inclusion of a charge injection structure for trap suppression and a reduction in the register channel width. The improvement in tolerance to radiation induced serial CTI achieved by reducing the channel width from 50 um to 20 um was measured experimentally to be a factor of 1.7, which compares well to a factor of 1.9 found using a charge volume model