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.
KEYWORDS: Charge-coupled devices, Solar radiation models, Space operations, Data modeling, Magnetosphere, Fourier transforms, Testing and analysis, Solar processes, Performance modeling, Data acquisition
Charge coupled devices (CCDs) have been the detector of choice for large-scale space mission for many years. Although dominant in this field, the charge transfer performance of the technology degrades over time due to the harsh space- radiation environment. Charge transfer performance can be optimized however, but it is often time consuming and expensive due to the many operating modes of the CCDs. A new technique is presented and developed here, which uses new measurements of the trap landscape present in a CCD, to predict changes in charge transfer inefficiency as a function of different variables. By using this technique, it is possible to focus experimental lab testing on key device parameters, potentially saving many months of laboratory effort. Due to the generality of the method, it can be used to optimize the charge transfer performance of any CCD, and as such has many uses across a wide range of fields. Future CCDs variants that will be used in potential space missions (EMCCD and p-channel CCDs) can use this technique to feedback key device performance to the wider mission consortium before devices are available for experimental testing.
The joint European Space Agency and Chinese Academy of Sciences Solar wind Magnetosphere Ionosphere Link Explorer mission (SMILE) aims to develop a global scale understanding of the interaction between the solar weather and the Earth’s magnetosphere-ionosphere. The soft X-ray imager (SXI) is one of the instruments on board and will observe photons emitted in the 200 eV to 2000 eV energy range from the solar wind charge exchange process using two large 4510 x 4510 pixel CCD370s as a focal plane. The CCD370s take their design and qualification heritage from similar sensors being used in the PLATO mission, with specific modifications to optimize their performance in this soft X-ray energy range. SMILE will orbit Earth in a highly elliptical orbit and will pass through the radiation belts every 52 hours. The trapped and solar protons present will gradually damage the CCDs throughout the 3-year mission and degrade their performance. To understand the impact the damage has on the devices a series of proton radiation campaigns are being undertaken. These campaigns are being performed with flight-like SMILE CCDs, and functionally similar PLATO devices, with follow-up characterization across from -130 to -85 °C. The most recent irradiation campaign has been completed using a PLATO CCD280 kept below -85 °C for irradiation and characterization, and the results show that the measured parallel charge transfer inefficiency varies with temperature between 1x10-4 and 4x10-4 in unbinned full-frame readout mode. The effect of temperature annealing up to -85 °C on the parallel charge transfer inefficiency has also been assessed and shows that no temperature-dependent annealing of the radiation-induced damage has been observed. A similar behavior is expected to be seen in the SMILE devices, albeit with an anticipated improvement by a factor 3-4 due to the modifications made to the design. Thus, results indicate the SMILE CCD370s will meet the performance requirements of the SMILE SXI instrument.
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.