Proton damage comparison of an e2v technologies n-channel and p-channel CCD204

Comparisons have been made of the relative degradation of charge transfer efficiency in n-channel and p-channel CCDs subjected to proton irradiation. The comparison described in this paper was made using e2v technologies plc. CCD204 devices fabricated using the same mask set. The device performance was compared over a range of temperatures using the same experimental arrangement and technique to provide a like-for-like comparison. The parallel transfer using the p-channel CCD was then optimized using a trap pumping technique to identify the optimal operating conditions at 153 K

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

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

A System of Subroutines For Iteratively Reweighted Least Squares Computations

A description of a system of subroutines to compute solutions to the iteratively reweighted least squares problem is presented. The weights are determined from the data and linear fit and are computed as functions of the scaled residuals. Iteratively reweighted least squares is a part of robust statistics where "robustness" means relative insensitivity to moderate departures from assumptions. The software for iteratively reweighted least squares is cast as semi-portable Fortran code whose performance is unaffected (in the sense that performance will not be degraded) by the computer or operating-system environment in which it is used. An [ell sub1] start and an [ell sub2] start are provided. Eight weight functions, a numerical rank determination, convergence criterion, and a stem-and-leaf display are included.

Darwin Meets Einstein: LISA Data Analysis Using Genetic Algorithms

This work presents the first application of the method of Genetic Algorithms (GAs) to data analysis for the Laser Interferometer Space Antenna (LISA). In the low frequency regime of the LISA band there are expected to be tens of thousands galactic binary systems that will be emitting gravitational waves detectable by LISA. The challenge of parameter extraction of such a large number of sources in the LISA data stream requires a search method that can efficiently explore the large parameter spaces involved. As signals of many of these sources will overlap, a global search method is desired. GAs represent such a global search method for parameter extraction of multiple overlapping sources in the LISA data stream. We find that GAs are able to correctly extract source parameters for overlapping sources. Several optimizations of a basic GA are presented with results derived from applications of the GA searches to simulated LISA data.Comment: 8 pages, 12 figure

Evolution and impact of defects in a p-channel CCD after cryogenic proton-irradiation

P-channel CCDs have been shown to display improved tolerance to radiation-induced charge transfer inefficiency (CTI) when compared to n-channel CCDs. However, the defect distribution formed during irradiation is expected to be temperature dependent due to the differences in lattice energy caused by a temperature change. This has been tested through defect analysis of two p-channel e2v CCD204 devices, one irradiated at room temperature and one at a cryogenic temperature (153K). Analysis is performed using the method of single trap pumping. 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 up until a cumulative anneal time of approximately 10 months. We have also simulated charge transfer in an irradiated CCD pixel using the defect distribution from both the room-temperature and cryogenic case, to study how the changes affect imaging performance. 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-tolerance testing

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

Optimisation of device clocking schemes to minimise the effects of radiation damage in charge-coupled devices

The European Space Agency Euclid mission aims to answer the question of how the universe originated through the mapping of the dark Universe. One method to investigate this geometry is to measure subtle changes in ellipticity using image sensors such as the charge-coupled device (CCD). However, the radiation environment in space plays a major part in the performance of CCD-based camera systems. When placed in space, a CCD becomes damaged by the radiation environment, and this can lead to a "smearing" of the charge, acting to change the ellipticity, and therefore, one must be able to separate the changes in ellipticity caused by radiation damage from those the mission aims to measure. To this end, the radiation-damage-induced shape changes require an in-depth investigation such that optimized operation can be achieved. A Monte Carlo simulation is being used to predict this impact, backed by experimental data from a detector formerly baselined for the mission. During the experimental study, an investigation was undertaken into the serial readout of the CCD to demonstrate an approach toward performance optimization through a consideration of the trap species involved. A change in the clocking scheme was found to result in a factor of 3 reduction in charge transfer inefficiency

Bayesian Methods in the Search for MH370

Probability theor

Modelling charge transfer in a radiation damaged charge coupled device for Euclid

As electrons are transferred through a radiation damaged Charge Coupled Device (CCD), they may encounter traps in the silicon in which they will be captured and subsequently released. This capture and release of electrons can lead to a 'smearing' of the image. The dynamics of the trapping process can be described through the use of Shockley-Read-Hall theory, in which exponential time constants are used to determine the probability of capture and release. If subjected to a hostile radiation environment, such as in space where the dominant charged particle is the proton, these incident protons can cause displacement damage within the CCD and lead to the formation of stable trap sites. As the trap density increases, the trapping and release of signal electrons can have a major impact on the Charge Transfer Efficiency (CTE) to the detriment of device performance. As the science goals for missions become ever more demanding, such as those for the ESA Euclid and Gaia missions, the problem of radiation damage must be overcome. In order to gain a deeper understanding of the trapping process and the impact on device performance, a Monte Carlo simulation has been developed to model the transfer of charge in a radiation damaged CCD. This study investigates the various difficulties encountered when developing such a model: the incorporation of appropriate clocking mechanisms, the use of suitable trap parameters and their degeneracy, and the development of methods to model the charge storage geometry within a pixel through the use of three-dimensional Silvaco simulations