No abstract

Back-thinned silicon detectors offer a high response over a very broad spectrum for direct detection by providing an efficient optical path into the sensing silicon avoiding front face structures manufactured from metal, polysilicon, nitrides and oxides that may absorb the incident light before reaching the sensing silicon. We have tested two CCDs with different back-surface shallow p+ implant thicknesses (basic and enhanced) at the M4 line (wavelength between 40 and 400 nm) at PTB's Metrology Light Source in Berlin. This characterisation in the ultraviolet spectral range extends the soft X-ray Quantum Efficiency dataset previously acquired with the exact same devices. Due to the short absorption depth and the scope for many types of interactions of the device materials with ultraviolet photons, Quantum Efficiency measurement and stability of the device against extended exposure in the UV is of ongoing interest. Therefore, Quantum Efficiency measurements have been carried out before and after exposures to quantify any change in behaviour. To allow characterisation of the passivation processes only, the devices have no anti-reflection coating. The measured Quantum Efficiency of the standard backthinned CCD is below 10 % between 70 nm and 370 nm. An average additional 5 % efficiency is achieved in the enhanced device within the same range. At the limits of the measured spectrum, towards soft X-ray or towards the visible range, the Quantum Efficiency increases and the difference between the standard and the enhanced process is reduced as the photon absorption length increases beyond the immediate back surface. The measured Quantum Efficiency after long high fluxes exposures at 200 nm shows remarkable improvement.

Throughout a typical Earth orbit a satellite is constantly bombarded by radiation with trapped and solar protons being of particular concern as they gradually damage the focal plane devices throughout the mission and degrade their performance. To understand the impact the damage has on CCDs and how it varies with their thermal history a proton radiation campaign has been carried out using a CCD280. The CCD is irradiated at 153 K and gradually warmed to 188 K in 5 K increments with Fe55 X-ray, dark current and trap pumping images taken at 153 K after each anneal step. The results show that despite the trap landscape changing throughout the anneal it has little impact on parallel charge transfer inefficiency. This is thought to be because most traps are unaffected and a lot of those that do anneal only move from the continuum between distinct trap species and into a nearby divacancy trap “peak” whose emission time constant is similar enough to still impact the CTI. In terms of using a CCD280 or similar devices in a mission the CTI being unaffected by thermal annealing up to 188 K means that any CTI correction needed as the radiation damage builds up does not have to take into account the thermal history of the focal plane. However, it is possible that a significant amount of annealing will occur at temperatures greater than 188 K and care should be taken when a mission is operating in this range to gather accurate pre-flight data.

Teledyne-e2v's sensors and wafer-scale processing are widely used for high performance imaging across soft X-ray and optical bands. In the ultraviolet spectral range, the combination of short absorption lengths (below 10 nm) and high reflectance (up to 75 %) can strongly limit the quantum efficiency. Direct detection capability relies on back-illumination and back-thinning processes to be applied to a sensor to remove dead layers from the optical path. As the thinning process leaves an unacceptably thick backside potential well as well as a highly reflective surface, in-house ultraviolet-specific (e.g. for WUVS) or third-party processes (e.g. delta-doping for FIREBall) are required.We have calibrated Teledyne-e2v's latest in-house wafer-scale proprietary processes with monochromatic synchrotron radiation over a wide spectral range in the ultraviolet domain (λ=40 nm -400 nm) at the Metrology Light Source of the Physikalisch-Technische Bundesanstalt. The first process is a shallow p+ implantation that permits the thinning of the backside potential well. It is available in two different levels: basic and enhanced. The second type of enhancement is a specific anti-reflective coating to increase the back-surface transmittance for distinct spectral ranges.In this paper, we will present comparative quantum efficiency calibration of both passivation stages and of two different ultraviolet specific anti-reflective coatings (applied on enhanced passivation devices). Also, their stability after intense ultraviolet illumination will be shown. These measurements will permit Teledyne-e2v to extend the quantum efficiency data of their most recent processes across the soft X-ray to near-infrared spectrum.

SMILE (Solar Magnetosphere Ionosphere Link Explorer) is a collaborative mission between the European Space Agency and the Chinese Academy of Sciences that is scheduled to be launched in 2024 and will be placed in a highly elliptical, inclined, orbit. The on-board instrumentation will study interactions between the solar wind and the Earth's magnetosphere-ionosphere system by imaging the soft X-ray emission that results from solar wind charge exchange whilst simultaneously collecting information about the northern aurora with a UV imager and investigating the solar wind and magnetosheath plasma and magnetospheric field conditions using a Light Ion Analyzer and a magnetometer.The SXI (Soft X-ray Imager) is a wide field 'lobster-eye' telescope that is equipped with two 4510 x 4510 pixel CCDs with 18 µm pixel pitch. It will image X-rays (300 eV-2000 eV) through focusing optics that consist of an array of Micro Pore plates.The predicted X-ray event rate is expected to be low and the instrument will operate in photon counting mode so the SXI is designed to maximize the useful information returned to earth by identifying and storing individual events on board the spacecraft before transmitting the relevant information back to earth. This study investigates the baseline methods that will be implemented on-board to isolate and extract these events from the images amongst a more complicated particle background. The detector response is modelled and verified with calibration data from the CCD270.The work presented here by the Centre for Electronic Imaging at the Open University demonstrates the proposed method for isolating individual soft X-rays from images taken using the SMILE SXI and subsequently sorting these X-rays into data packets suitable for transmitting to earth. Different methods are tested with simulated and real data to optimize the proportion of useful events transmitted.