A gamma, x-ray and high energy proton radiation-tolerant CIS for space applications

Photon counting is useful in space-based imagers wherever quantitative light- intensity evaluation is necessary. Various types of radiation, from cosmic rays to high-energy proton beams to gamma radiation, have an effect on the functionality and accuracy of imagers and the literature is extensive. Techniques to maximize sensor tolerance have also been developed for a number of years and several imagers resistant to up to 30Mrad (Si) of gamma radiation have been reported. These sensors have several shortcomings: either significant noise performance degradation, up to several orders of magnitude, or unacceptably high pre-radiation noise levels. In addition, many radiation-tolerant sensors use dedicated processes, thus possibly limiting their suitability for mass-market applications. This paper describes a CMOS photon-counting imager designed to detect the Earth's airglow, which is the atmospheric oxygen emission at 762 nm due to oxygen recombination. Airglow occurs day and night and enables geostationary and orbiting satellites to infer their position referred to the Earth's center for attitude determination. The goal is to develop a sensor that reduces the requirements on weight and size of navigational telescope optics mounted on an ultra- low-cost micro-satellite.

Low Cost Earth Sensor Based on Oxygen Airglow (AIRES)

Edoardo Charbon, Noémy Scheidegger, Herbert Shea

This project has demonstrated the feasibility of a low-cost Earth sensor based on imaging oxygen airglow, allowing 0.4° accuracy from GEO under any illumination condition. Available Earth Sensor (ES) are based on the measurement of the earth’s infrared radiation to determine the vector to the Earth’s centre. These designs provide excellent accuracies over a large field of view, but are often heavy, large, require cooling or temperature stabilization and are power hungry. In addition, the sensor concept for a LEO or GEO application ES differs significantly. We have developed a novel ES concept for applications where milli-degree accuracy is not required, but where low-cost is essential and lower (about 1 – 5°) accuracy is acceptable. Such a sensor could be used in new scenarios and to improve spacecraft reliability by providing a low-cost back-up sensor. Our Earth Sensor concept is based on imaging atmospheric oxygen emission at 762 nm using highly sensitive detectors. In both night-time and daytime there is continuous emission at 762 nm due to oxygen recombination. Low-noise active pixel sensors (APS) or low-light detector based on arrays of single photon avalanche diodes (SPAD) enables the ES to operate at night and day, over a wide temperature range, with a very compact optical system (aperture of 8 mm, focal length of 11 mm) and no scanning elements. A modular design allows designing similar instruments using the same wavelength band, the same detector technology, the same optics, the same power and data interfaces and similar algorithms for GEO and LEO applications, thus reducing the development cost. We have developed an Earth appearance model at 762 nm, which was used as input for the mechanical, optical and electric design of the Earth Sensor (conceptual design). In order to achieve a low-cost solution, simplicity and reduction of part count was a driving factor in the design trade-offs. Total mass for the GEO design is 845 g with a mean power consumption of 4 W. Algorithms were developed to determine the vector to the Earth from the images. A breadboard was built to display a simulated picture of the Earth under varying conditions, image those pictures at different temperatures with a radiation tolerant APS (LCMS), and verify the correct operation of the algorithms. In addition to the conceptual design and breadboard level demonstration of key technologies, a novel detector chip was designed and fabricated: a radiation-tolerant array of single photon avalanche photodiodes (SPAD) build using conventional 0.35 μm CMOS technology. The chip was tested under proton and gamma irradiation, and operated with only minor changes in dark current after 30 krad TID. Having shown the feasibility of such an Earth Sensor, this work concluded with a development plan to lead to a flight model.

2008

The effects of gamma-radiation on the properties of Brillouin scattering in standard Ge-doped optical fibres

Laura Abrardi, Dario Alasia, Luc Thévenaz

We have experimentally studied the effects of gamma-radiation up to very high total doses on the physical properties of Brillouin scattering in standard commercially available optical fibres. A frequency variation of about 5 MHz for both Brillouin frequency and linewidth has been measured at the total dose of about 10 MGy. The radiation-induced shift has a negligible practical impact and makes Brillouin scattering very immune to radiation, so that distributed sensors based on this interaction exhibit an interesting potential for use in nuclear facilities. © 2006 IOP Publishing Ltd.

Institute of Physics2006

High-Performance CMOS SPAD-Based Sensors for Time-of-Flight PET Applications

Francesco Gramuglia

Detecting light, photon by photon, has been possible since the 1930s, with the invention of the photomultiplier tube (PMT). However, it is only since the 1970s, that solid-state single-photon detectors have emerged and only since 2003 that a new technology, known as single-photon avalanche diode (SPAD) has become CMOS-compatible.The SPAD technology is scalable, low-cost, and it is natively digital, thereby enabling a variety of sensor architectures optimized for applications, such as bioimaging, high energy physics, and medical physics. Thanks to the adaptability of SPADs to many different CMOS technologies, it is possible to achieve systems of different complexity, operating conditions, and, ultimately, cost. The versatility of this device, makes it ideal in very different applications, where it is emerging as the sensor of choice.This thesis focuses on improving CMOS SPAD performance for time-of-flight PET, while other applications, such as FLIM and LiDAR could also benefit from the technology developed here.We have designed SPAD-based sensors in two different silicon standard technology nodes and we have fully analyzed their performance. We have also explored the optimization of light extraction in inorganic scintillator-based detector modules and direct particle detection and we have studied two applications beyond PET.The thesis is organized as follows. After a comprehensive description of SPAD technology, we focus on new SPADs structures in standard deep-submicron technology nodes, 180 nm CMOS and 55 nm BCD. The results achieved with these devices show how SPADs can achieve an unprecedented timing performance of 7.5 ps FWHM at room temperature with a sensitivity peak of 55% thanks to a fully integrated front-end readout system that is shown to play an essential role here.We show that state-of-the-art performance is possible using advanced standard technology nodes, where outstanding timing and sensitivity performance were achieved by systematically engineering the electric field in multiplication and drift regions to achieve optimized carrier generation and transport upon detection.We have demonstrated the first large-scale 3D-stacked frontside-illuminated (FSI) multi-digital silicon photomultiplier (MD-SiPM), whereas we discuss the sensor structure and its electronic components aimed at modularity and scalability, so as to ultimately achieve large-format SPAD sensors.To demonstrate specific aspects of the intended applications, in primis, TOF-PET, we look at coupling between photodetectors and inorganic scintillators, where gamma radiations, originated from electron-positron annihilations, are detected. Using photonic crystals structures, nanoimprinted on the scintillator output surface, we have demonstrated a 40% improvement in light extraction and 25% better energy resolution in BGO crystals.Finally, we explore the use of SPADs for direct time-of-flight coincidence measurements of minimum ionizing particles. We achieved an unprecedented 9.4 ps coincidence uncertainty in this novel and very thought-provoking SPAD application, corresponding to a 6 ps Gaussian sigma timing resolution for a single detector.In summary, this thesis demonstrates new paradigms of SPAD performance, together with a novel 3D integration of FSI SPADs, and novel application solutions. In the future, we thus expect that these achievements will pave the way for further performance improvements and extensive scientific explorations.