CMOS image sensors are widely used on Earth and are becoming increasingly favourable for use in space. Advantages, such as low power consumption, and ever-improving imaging peformance make CMOS an attractive option. The ability to integrate camera functions on-chip, such as biasing and sequencing, simplifies designing with CMOS sensors and can improve system reliability. One potential disadvantage to the use of CMOS is the possibility of single event effects, such as single event latchup (SEL), which can cause malfunctions or even permanent destruction of the sensor. These single event effects occur in the space environment due to the high levels of radiation incident on the sensor. This work investigates the ocurrence of SEL in CMOS image sensors subjected to heavy-ion irradiation. Three devices are investigated, two of which have triple-well doping implants. The resulting latchup cross-sections are presented. It is shown that using a deep p well on 18 μm epitaxial silicon increases the radiation hardness of the sensor against latchup. The linear energy transfer (LET) threshold for latchup is increased when using this configuration. Our findings suggest deep p wells can be used to increase the radiation tolerance of CMOS image sensors for use in future space missions.
Time Delay and Integration (TDI) is used to increase the Signal to Noise Ratio (SNR) in image sensors when imaging fast moving objects. One important TDI application is in Earth observation from space. In order to operate in the space radiation environment, the effect that radiation damage has on the performance of the image sensors must be understood.
This work looks at prototype TDI sensor pixel designs, produced by e2v technologies. The sensor is a CCD-like charge transfer device, allowing in-pixel charge summation, produced on a CMOS process. The use of a CMOS process allows potential advantages such as lower power consumption, smaller pixels, higher line rate and extra on-chip functionality which can simplify system design. CMOS also allows a dedicated output amplifier per column allowing fewer charge transfers and helping to facilitate higher line rates than CCDs.
In this work the effect on the pixels of radiation damage from high energy protons, at doses relevant to a low Earth orbit mission, is presented. This includes the resulting changes in Charge Transfer inefficiency (CTI) and dark signal.
Euclid-VIS is the large format visible imager for the ESA Euclid space mission in their Cosmic Vision program,
scheduled for launch in 2020. Together with the near infrared imaging within the NISP instrument, it forms the basis of
the weak lensing measurements of Euclid. VIS will image in a single r+i+z band from 550-900 nm over a field of view
of ~0.5 deg2. By combining 4 exposures with a total of 2260 sec, VIS will reach to V=24.5 (10σ) for sources with extent
~0.3 arcsec. The image sampling is 0.1 arcsec. VIS will provide deep imaging with a tightly controlled and stable point
spread function (PSF) over a wide survey area of 15000 deg2 to measure the cosmic shear from nearly 1.5 billion
galaxies to high levels of accuracy, from which the cosmological parameters will be measured. In addition, VIS will also
provide a legacy dataset with an unprecedented combination of spatial resolution, depth and area covering most of the
extra-Galactic sky. Here we will present the results of the study carried out by the Euclid Consortium during the period
up to the Preliminary Design Review.
The focal plane array of the Euclid VIS instrument comprises 36 large area, back-illuminated, red-enhanced CCD detectors (designated CCD 273). These CCDs were specified by the Euclid VIS instrument team in close collaboration with ESA and e2v technologies. Prototypes were fabricated and tested through an ESA pre-development activity and the contract to qualify and manufacture flight CCDs is now underway. This paper describes the CCD requirements, the design (and design drivers) for the CCD and package, the current status of the CCD production programme and a summary of key performance measurements.
Applications at synchrotron facilities such as macromolecular crystallography and high energy X-ray diffraction require
high resolution imaging detectors with high dynamic range and large surface area. Current systems can be split into two
main categories: hybrid pixel detectors and scintillator-coupled Charge-Coupled Devices (CCDs). Whilst both have
limitations, CCD-based systems (coupled to fibre-optics to increase imaging area) are often used in these applications
due to their small pixels and the high resolution. Electron-Multiplication CCDs (EM-CCDs) are able to suppress the
readout noise associated with increased readout speed offering a low noise, high speed detector solution. A previous
pilot study using a small-area (8 mm × 8 mm) scintillator-coupled EM-CCD found that through high frame-rates, low
noise and novel uses of photon-counting, resolution could be improved from over 80 μm to 25 μm at 2 fps. To further
improve this detector system, high speed readout electronics can be used alongside a fibre-optic taper and EM-CCD to
create a “best of both worlds” solution consisting of the high resolution of a CCD, along with the low noise, high speed
(high dynamic range) and large effective area of pixel detectors. This paper details the developments in the study and
discusses the latest results and their implication on the system design.
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 μm to 20 μm 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
PLATO is a candidate mission for an European Space Agency M-class launch opportunity. The project aims to detect
exo-planets from their transits across host stars and to characterise those stars by studying their oscillations, hence the
name PLATO for, PLAnetary Transits and Oscillations of stars. In order to achieve this aim the mission proposes to fly a
satellite with a focal plane of up to 34 mini-telescopes, each containing 4 large area back illuminated Charge-Coupled
Devices (CCDs) to provide ultra high precision photometry. If successful, the satellite will have nearly 0.9 m2 of image
sensors and will be by far the largest composite detector focal plane ever flown. To meet the mission requirements e2v
have developed the CCD270 which has 4510 by 4510 pixels, each pixel is 18 μm by 18 μm, in a development funded by
the European Space Agency. This large area (81 mm x 81 mm) full frame image sensor is intended for precision
photometry with a dynamic range in excess of 30,000. The CCD270 has been manufactured with a thinner gate dielectric
and a higher buried channel dose than standard devices to increase the full well capacity in the image area. The
additional advantages of the thinner gate are lower power dissipation, smaller clock voltage swing for standard channel
doses and higher tolerance to ionising radiation. This paper describes the imager sensor in detail and focuses on the novel
aspects of the device, package and interface.
The charge transfer efficiency of a CCD is based on the average level of signal lost per pixel over a number of transfers. This value can be used to directly compare the relative performances of different structures, increases in radiation damage or to quantify improvements in operating parameters. This number does not however give sufficient detail to mitigate for the actual signal loss/deference in either of the transfer directions that may be critical to measuring shapes to high accuracy, such as those required in astronomy applications (e.g. for Gaia’s astrometry or the galaxy distortion measurements for Euclid) based in the radiation environment of space. Pocket-pumping is an established technique for finding the location and activation levels of traps; however, a number of parameters in the process can also be explored to identify the trap species and location to sub-pixel accuracy. This information can be used in two ways to increase the sensitivity of a camera. Firstly, the clocking process can be optimised for the time constant of the majority of traps in each of the transfer directions, reducing deferred charge during read out. Secondly, a correction algorithm can be developed and employed during the post-processing of individual frames to move most of any deferred signal back into the charge packet it originated from. Here we present the trap-pumping techniques used to optimise the charge transfer efficiency of p- and n-channel e2v CCD204s and describe the use of trap-pumped images for on-orbit calibration and ground based image correction algorithms.
The European Space Agency has funded e2v’s development of an image sensor for the visible instrument in the Euclid
space telescope. Euclid has been selected for a medium class mission launch opportunity in 2020. The project aims to
map the dark universe with two complementary methods; a galaxy red-shift survey and weak gravitational lensing using near infrared and visible instruments. The baseline for the visible instrument was to be the CCD203-82, which has been successfully flown on NASA’s Solar Dynamics Observatory. However, to optimise the device for Euclid, e2v have designed and manufactured the CCD273-84. This device has a higher-responsivity lower-noise amplifier, enhanced red response, parallel charge injection structures and narrower registers which improve low signal charge transfer efficiency. Development models for Euclid have been manufactured with a thinner gate dielectric than standard for improved tolerance to ionising radiation. This paper describes the imager sensor in detail and focuses on the novel aspects of the device, package and interface.
KEYWORDS: Charge-coupled devices, Calibration, Point spread functions, Galactic astronomy, Sensors, Staring arrays, Camera shutters, Space operations, Radiation effects, Imaging systems
Euclid-VIS is a large format visible imager for the ESA Euclid space mission in their Cosmic Vision program, scheduled
for launch in 2019. Together with the near infrared imaging within the NISP instrument it forms the basis of the weak
lensing measurements of Euclid. VIS will image in a single r+i+z band from 550-900 nm over a field of view of ~0.5
deg2. By combining 4 exposures with a total of 2240 sec, VIS will reach to V=24.5 (10σ) for sources with extent ~0.3
arcsec. The image sampling is 0.1 arcsec. VIS will provide deep imaging with a tightly controlled and stable point spread
function (PSF) over a wide survey area of 15000 deg2 to measure the cosmic shear from nearly 1.5 billion galaxies to
high levels of accuracy, from which the cosmological parameters will be measured. In addition, VIS will also provide a
legacy imaging dataset with an unprecedented combination of spatial resolution, depth and area covering most of the
extra-Galactic sky. Here we will present the results of the study carried out by the Euclid Consortium during the Euclid
Definition phase.
CCDs have been used on several successful X-ray space missions including high resolution soft X-ray spectrometers,
such as the Reflection Grating Spectrometer on XMM-Newton1 and the LETG and HETG on Chandra2. These
instruments had a resolving power of ( E / Δ E) ~300; however, with new technology this can be improved allowing resolution
to the thermal limit. In the soft X-ray band (200 eV to 10 keV) a resolution of around 3000 is required resolve all of the
possible absorption and emission features. Through the development of instruments for the OP-XGS on IXO3 and the
WHIMEx explorer mission4 it has been shown that an instrument capable of this resolution on a spacecraft is possible.
CCDs are the ideal detector for use in detection of X-rays at this energy as they provide positional information allowing
a high level of spatial resolution and their inherent energy resolution allowing diffracted orders to be separated. This
paper will investigate the use of CCDs and possible use of EM-CCDs in soft X-ray spectroscopy. The multiplication of
signal in the charge domain can increase the detectability of low energy photons, improving the Signal-to-Noise Ratio.
Multiplication gain has been shown to degrade the resolution of a device as described by the Modified Fano Factor5, so
this has to be taken into account in instrument design when overlapping spectral orders are needed to achieved the
necessary resolution. The use of optical filters on the CCDs and their effect on quantum efficiency at soft X-ray energies
is discussed together with possible improvements to existing technology.
The Open University, in collaboration with e2v technologies and XCAM Ltd, have been selected to fly an EO
(Earth Observation) technology demonstrator and in-orbit radiation damage characterisation instrument on
board the UK Space Agency's UKube-1 pilot Cubesat programme. Cubesat payloads offer a unique opportunity
to rapidly build and fly space hardware for minimal cost, providing easy access to the space environment. Based
around the e2v 1.3 MPixel 0.18 micron process eye-on-Si CMOS devices, the instrument consists of a radiation
characterisation imager as well as a narrow field imager (NFI) and a wide field imager (WFI). The narrow and
wide field imagers are expected to achieve resolutions of 25 m and 350 m respectively from a 650 km orbit,
providing sufficient swathe width to view the southern UK with the WFI and London with the NFI. The
radiation characterisation experiment has been designed to verify and reinforce ground based testing that has
been conducted on the e2v eye-on-Si family of devices and includes TEC temperature control circuitry as well
as RADFET in-orbit dosimetry. Of particular interest are SEU and SEL effects. The novel instrument design
allows for a wide range of capabilities within highly constrained mass, power and space budgets providing a
model for future use on similarly constrained missions, such as planetary rovers. Scheduled for launch in
December 2011, this 1 year low cost programme should not only provide valuable data and outreach
opportunities but also help to prove flight heritage for future missions.
Charge-Coupled Devices (CCDs) have been traditionally used on high resolution soft X-ray spectrometers, but
with their ability to increase the signal level in the detector before the readout noise of the system is added,
Electron-Multiplying CCDs (EM-CCDs) have the potential to offer many advantages in soft X-ray detection.
Through this signal multiplication an EM-CCD has advantages over conventioanl CCDs of increased signal,
suppressed noise, faster readout speeds for the same equivalent readout noise and an increased inmmunity to
Electro-Magnetic Intereference. This paper will look at present and future spacel applications for high resolution
soft X-ray spectrometers and assess the advantages and disadvantage of using EM-CCDs in these applications.
Euclid-VIS is a large format visible imager under investigation for the ESA Euclid space mission in their Cosmic Vision
program. Together with the near infrared photometer (NIP) it forms the basis of the weak lensing measurements of
Euclid. VIS will image in a single r+i+z band from 550-920 nm over a field of view of ~0.5 deg2. Over 4 exposures
totalling 1800 sec, VIS will reach to V=24.9 (10σ) for sources with extent ~0.3 arcsec. The image sampling is 0.1
arcsec. VIS will provide deep imaging with a tightly controlled and stable PSF over a wide surcey area of of 20000 deg2
to measure the cosmic shear from over 2 billion galaxies to high levels of accuracy, from which the cosmological
parameters will be measured. In addition, VIS will also provide a legacy deep imaging dataset of unprecedented spatial
resolution over the entire extra-Galactic sky. Here we will present the results of the study carried out by the Euclid
Imaging Consortium during the Euclid Assessment Phase.
The International X-ray Observatory (IXO) is a collaborative effort between NASA, ESA, and JAXA. The IXO science
goals are heavily based on obtaining high quality X-ray spectra. In order to achieve this goal the science payload will
incorporate an array of gratings for high resolution, high throughput spectroscopy at the lowest X-ray energies, 0.3 - 1.0
keV. The spectrometer will address a number of important astrophysical goals such as studying the dynamics of clusters
of galaxies, determining how elements are created in the explosions of massive stars, and revealing most of the "normal"
matter in the universe which is currently thought to be hidden in hot filaments of gas stretching between galaxies. We
present here a mature design concept for an Off-Plane X-ray Grating Spectrometer (OP-XGS). This XGS concept has
seen recent significant advancements in optical and mechanical design. We present here an analysis of how the baseline
OP-XGS design fulfills the IXO science requirements for the XGS and the optical and mechanical details of this design.
The International X-ray Observatory (IXO) is a merger of the former ESA XEUS and NASA Constellation-X missions,
with additional collaboration from JAXA, proposed for launch ~2020. IXO will address the leading astrophysical
questions in the 'hot universe' through its breakthrough capabilities in X-ray spectroscopy. The mission covers the 0.1
to 40 keV energy range, complementing the capabilities of the next generation observatories, such as ALMA, LSST,
JWST and 30 meter ground-based telescopes. An X-ray Grating Spectrometer is baselined to provide science in the
energy range 0.3-1.0 keV at a spectral resolution of E/ΔE > 3,000 with an effective area greater than 1,000 cm2. This
will require an array of soft X-ray enhanced CCDs operating at a modest frame rate to measure the diffracted light in
both position and energy. Here we describe the baseline camera for the Off-plane XGS instrument using mature CCD
technology.
CCDs are regularly used as imaging and spectroscopic devices on space telescopes at X-ray energies due to their
high quantum efficiency and linearity across the energy range. The International X-ray Observatory's X-ray
Grating Spectrometer will also look to make use of these devices across the energy band of 0.3 keV to 1 keV.
At these energies, when photon counting, the charge generated in the silicon is close to the noise of the system.
In order to be able to detect these low energy X-ray events, the system noise of the detector has to be minimised
to have a sufficient signal-to-noise-ratio. By using an EM-CCD instead of a conventional CCD, any charge that
is collected in the device can be multiplied before it is read out and as long as the EM-CCD is cool enough to
adequately suppress the dark current, the signal-to-noise ratio of the device can be significantly increased,
allowing soft X-ray events to be more easily detected.
This paper will look into the use of EM-CCDs for the detection of low energy X-rays, in particular the effect
that using these devices will have on the signal to noise ratio as well as any degradation in resolution and
FWHM that may occur due to the additional shot noise on the signal caused by the charge packet amplification
process.
The International X-ray Observatory (IXO) project is the result of a merger between the NASA Con-X and ESA/Jaxa
XEUS mission concepts. The IXO mission outline has an X-ray grating spectrometer operating in the 0.3-1 keV band.
CCDs are the ideal detector for the readout of the grating spectrometer instrument and have been flown in similar
functions on XMM and Chandra. Here we review the Off-Plane X-ray Grating Spectrometer concept for IXO and
discuss the optimization of CCD technology for detection in the 0.2-2 keV X-ray band. We will discuss improvements to
the existing technology previously flown, and the use of new technology such as electron multiplying CCDs which can
provide enhanced signal to noise at these soft X-ray energies, together with radiation hardening measures and methods of
reducing sensitivity to optical stray light. We will also end by discussing alternative CMOS-based technology which may
be developed in future years to replace the CCD technology, offering benefits of higher system integration and radiation
hardness.
e2v have been developing new approaches to mitigate against the effects of radiation damage in CCD sensors. The first of these is our "rad-hard" device technology, primarily developed to reduce the flat-band voltage shift following ionising radiation. With this a very significant improvement has been demonstrated, the flat-band shift reducing from typically 100-200 mV/kRad(Si) with standard devices to only 6 mV/kRad(Si), plus an associated reduction in the increase in surface dark signal. The rad-hard process thereby allows
devices to be operated in environments with up to at least 500kRad total dose and/or with reduced shielding.
Developments aimed at reducing the impact of proton radiation have included the manufacture of p-channel devices. Our initial data indicates that at -50°C the increase in charge transfer inefficiency is reduced by a factor of two times for parallel transfer and five times for serial transfer.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.