Today, both CCD and CMOS sensors can be envisaged for nearly all visible sensors and instruments designed for space needs. Indeed, detectors built with both technologies allow excellent electro-optics (EO) performances to be reached, the selection of the most adequate device being driven by their functional and technological features and limits. The first part of the paper shortly recalls how far CMOS Image Sensors (CIS) EO performances have been improved these last years. The second part reviews the advantages of CMOS technology for space applications, illustrated by examples of CIS developments performed by EADS Astrium and Supaéro/CIMI for current and short term coming space programs.
Imaging detectors are key elements for optical instruments and sensors on board space missions dedicated to Earth observation (high resolution imaging, atmosphere spectroscopy...), Solar System exploration (micro cameras, guidance for autonomous vehicle...) and Universe observation (space telescope focal planes, guiding sensors...). This market has been dominated by CCD technology for long. Since the mid- 90s, CMOS Image Sensors (CIS) have been competing with CCDs for more and more consumer domains (webcams, cell phones, digital cameras...). Featuring significant advantages over CCD sensors for space applications (lower power consumption, smaller system size, better radiations behaviour...), CMOS technology is also expanding in this field, justifying specific R&D and development programs funded by national and European space agencies (mainly CNES, DGA, and ESA). All along the 90s and thanks to their increasingly improving performances, CIS have started to be successfully used for more and more demanding applications, from vision and control functions requiring low-level performances to guidance applications requiring medium-level performances. Recent technology improvements have made possible the manufacturing of research-grade CIS that are able to compete with CCDs in the high-performances arena. After an introduction outlining the growing interest of optical instruments designers for CMOS image sensors, this talk will present the existing and foreseen ways to reach high-level electro-optics performances for CIS. The developments of CIS prototypes built using an imaging CMOS process and of devices based on improved designs will be presented.
Solid-state optical sensors are now commonly used in space applications (navigation cameras, astronomy imagers, tracking sensors...). Although the charge-coupled devices are still widely used, the CMOS image sensor (CIS), which performances are continuously improving, is a strong challenger for Guidance, Navigation and Control (GNC) systems. This paper describes a 750x750 pixels CMOS image sensor that has been specially designed and developed for star tracker and tracking sensor applications. Such detector, that is featuring smart architecture enabling very simple and powerful operations, is built using the AMIS 0.5μm CMOS technology. It contains 750x750 rectangular pixels with 20μm pitch. The geometry of the pixel sensitive zone is optimized for applications based on centroiding measurements. The main feature of this device is the on-chip control and timing function that makes the device operation easier by drastically reducing the number of clocks to be applied. This powerful function allows the user to operate the sensor with high flexibility: measurement of dark level from masked lines, direct access to the windows of interest… A temperature probe is also integrated within the CMOS chip allowing a very precise measurement through the video stream. A complete electro-optical characterization of the sensor has been performed. The major parameters have been evaluated: dark current and its uniformity, read-out noise, conversion gain, Fixed Pattern Noise, Photo Response Non Uniformity, quantum efficiency, Modulation Transfer Function, intra-pixel scanning. The characterization tests are detailed in the paper. Co60 and protons irradiation tests have been also carried out on the image sensor and the results are presented. The specific features of the 750x750 image sensor such as low power CMOS design (3.3V, power consumption<100mW), natural windowing (that allows efficient and robust tracking algorithms), simple proximity electronics (because of the on-chip control and timing function) enabling a high flexibility architecture, make this imager a good candidate for high performance tracking applications.
Nowadays, CMOS image sensors are widely considered for space applications. The use of CIS (CMOS Image sensor)
processes has significantly enhanced their performances such as dark current, quantum efficiency and conversion gain.
However, in order to fulfil specific space mission requirements, dedicated research and development work has to be
performed to address specific detector performance issues. This is especially the case for dynamic range improvement
through output voltage swing optimisation, control of conversion gain and noise reduction. These issues have been
addressed in a 0.35μm CIS process, based on a large volume CMOS foundry, by several joint ISAE- EADS Astrium
R&D programs. These results have been applied to the development of the visible and near-infrared multi-linear imager
for the SENTINEL 2 mission (LEO Earth observation mission for the Global Measurement Environment and Security
program). For this high performance multi-linear device, output voltage swing improvement is achieved by process
optimisation done in collaboration with foundry. Conversion gain control is also achieved for each spectral band by
managing photodiode capacitance. A low noise level at sensor output is reached by the use of an architecture allowing
Correlated Double Sampling readout in order to eliminate reset noise (KTC noise). KTC noise elimination reveals noisy
pixels due to RTS noise. Optimisation of transistors's dimensions, taking into account conversion gain constraints, is
done to minimise these noisy pixels. Additional features have been also designed: 1) Due to different integration times
between spectral bands required by mission, a specific readout mode was developed in order to avoid electrical
perturbations during the integration time and readout. This readout mode leads to specific power supply architecture.
2)Post processing steps can be achieved by alignment marks design allowing a very good accuracy. These alignment
marks can be used for a black coating deposition between spectral bands (pixel line) in order to minimise straight light
effects. In conclusion a review of design improvements and performances of the final component is performed.
Sentinel 2 is an EU/ESA LEO Earth observation mission currently developed in the framework of Global Measurement
Environment and Security (GMES) program. The associated Multi Spectral Imager instrument is equipped with about
230 mm length VNIR and SWIR Focal Plane Arrays, each one being made of twelve detectors mechanically butted in
staggered configuration. Each elementary VNIR detector features tens spectral bands with 10m, 20m or 60m spatial
sampling, ranging from about 430 to 900 nm. The devices are currently manufactured using a 0.35 μm CMOS process
optimised for imaging application and already space qualified, thanks to Astrium COBRA family development. For each
spectral band, minimum SNR corresponding to reference flux and maximum integration time is required. Maximum flux
and minimum MTF are also specified. The photo detector charge to voltage conversion factors and geometrical shapes
have therefore been adjusted band per band in order to meet all these competing specifications. In addition, a per pixel
Correlated Double Sampling readout circuit has been implemented to cancel photodiode reset noise, providing mean
total readout noise lower than 200μV, and the output voltage swing has been improved in view of maximizing the device
dynamics. Black coating has been deposited between the simple or double lines of photo detectors in order minimizing
straight light effects. After a description of the multi linear detector architecture and functionality, its main performances
will be presented. The current status of the industrial development will also be depicted.
Nowadays, CMOS image sensors are widely considered for space applications. Their performances have been
significantly enhanced with the use of CIS (CMOS Image Sensor) processes in term of dark current, quantum efficiency
and conversion gain. Dynamic Range (DR) remains an important parameter for a lot of applications. Most of the
dynamic range limitation of CMOS image sensors comes from the pixel. During work performed in collaboration with
EADS Astrium, SUPAERO/CIMI laboratory has studied different ways to improve dynamic range and test structures
have been developed to perform analysis and characterisation. A first way to improve dynamic range will be described,
consisting in improving the voltage swing at the pixel output. Test vehicles and process modifications made to improve
voltage swing will be depicted. We have demonstrated a voltage swing improvement more than 30%. A second way to
improve dynamic range is to reduce readout noise A new readout architecture has been developed to perform a
correlated double sampling readout. Strong readout noise reduction will be demonstrated by measurements performed on
our test vehicle. A third way to improve dynamic range is to control conversion gain value. Indeed, in 3 TMOS pixel
structure, dynamic range is related to conversion gain through reset noise which is dependant of photodiode capacitance.
Decrease and increase of conversion gain have been performed with different design techniques. A good control of the
conversion gain will be demonstrated with variation in the range of 0.05 to 3 of initial conversion gain.
A novel principle has been developed to build an ultra wide dynamic range digital CMOS image sensor.
Multiple integrations are used to achieve the required dynamic. Its innovative readout system allows a direct capture of
the final image from the different exposure time with no need of external reconstruction. The sensor readout system is
entirely digital, implementing an in-pixel ADC. Realized in the STMicroelectronics 0.13&mgr;m CMOS standard technology,
the 10&mgr;m x 10&mgr;m pixels contain 42 transistors with a fill factor of 25%. The sensor is able to capture more than 120dB
dynamic range scenes at video rate.
Today, both CCD and CMOS sensors can be envisaged for nearly all visible sensors and instruments designed for space needs. Indeed, detectors built with both technologies allow excellent electro-optics performances to be reached, the selection of the most adequate device being driven by their functional and technological features and limits. The first part of the paper presents electro-optics characterisation results of CMOS Image Sensors (CIS) built with an optimised CMOS process, demonstrating the large improvements of CIS electro-optics performances. The second part reviews the advantages of CMOS technology for space applications, illustrated by examples of CIS developments performed by EADS Astrium and Supaero/CIMI for current and short term coming space programs.
With the growth of huge volume markets (mobile phones, digital cameras...) CMOS technologies for image sensor improve significantly. New process flows appear in order to optimize some parameters such as quantum efficiency, dark current, and conversion gain. Space applications can of course benefit from these improvements. To illustrate this evolution, this paper reports results from three technologies that have been evaluated with test vehicles composed of
several sub arrays designed with some space applications as target. These three technologies are CMOS standard, improved and sensor optimized process in 0.35μm generation. Measurements are focussed on quantum efficiency, dark current, conversion gain and noise. Other measurements such as Modulation Transfer Function (MTF) and crosstalk are depicted in . A comparison between results has been done and three categories of CMOS process for image sensors have been listed. Radiation tolerance has been also studied for the CMOS improved process in the way of hardening the imager by design. Results at 4, 15, 25 and 50 krad prove a good ionizing dose radiation tolerance applying specific techniques.
Imaging detectors are key elements for optical instruments and sensors on board space missions dedicated to Earth observation (high resolution imaging, atmosphere spectroscopy...), Solar System exploration (micro cameras, guidance for autonomous vehicle...) and Universe observation (space telescope focal planes, guiding sensors...). This market has been dominated by CCD technology for long. Since the mid-90s, CMOS Image Sensors (CIS) have been competing with CCDs for consumer domains (webcams, cell phones, digital cameras...). Featuring significant advantages over CCD sensors for space applications (lower power consumption, smaller system size, better radiations behaviour...), CMOS technology is also expanding in this field, justifying specific R&D and development programs funded by national and European space agencies (mainly CNES, DGA and ESA). All along the 90s and thanks to their increasingly improving performances, CIS have started to be successfully used for more and more demanding space applications, from vision and control functions requiring low-level performances to guidance applications requiring medium-level performances. Recent technology improvements have made possible the manufacturing of research-grade CIS that are able to compete with CCDs in the high-performances arena. After an introduction outlining the growing interest of optical instruments designers for CMOS image sensors, this paper will present the existing and foreseen ways to reach high-level electro-optics performances for CIS. The developments and performances of CIS prototypes built using an imaging CMOS process will be presented in the corresponding section.
This paper describes the development of a 750x750 pixels CMOS image sensor for star tracker applications. A first demonstrator of such a star tracker called SSM star tracker built around a 512x512 detector has been recently developed and proves the feasibility of such instrument. In order to take fully advantage of the CMOS image sensor step, the 750x750 device called SSM CMOS detector which will take part of the final star tracker, can be considered as a major technical breakthrough that gives a decisive advantage in terms of on satellite implementation cost and flexibility (sensor mass and power consumption minimisation, electronics and architecture flexibility). Indeed, built using the 0.5μm Alcatel Microelectronics standard CMOS technolgoy, the SSM CMOS detector will feature on-chip temperature sensor and on-chip sequencer. In order to evaluate the radiation tolerance of such manufacturing technology, a radiation campaign that contains studies of total dose and latch-up effects has been led on a specific test vehicle.
During the last 10 years, research about CMOS image sensors (also called APS - Active Pixel Sensors) has been intensively carried out, in order to offer an alternative to CCDs as image sensors. This is particularly the case for space applications as CMOS image sensors feature characteristics which are obviously of interest for flight hardware: parallel or semi-parallel architecture, on chip control and processing electronics, low power dissipation, high level of radiation tolerance... Many image sensor companies, institutes and laboratories have demonstrated the compatibility of CMOS image sensors with consumer applications: micro-cameras, video-conferencing, digital- still cameras. And recent designs have shown that APS is getting closer to the CCD in terms of performance level. However, he large majority of the existing products do not offer the specific features which are required for many space applications. ASTRIUM and SUPAERO/CIMI have decided to work together in view of developing CMOS image sensors dedicated to space business. After a brief presentation of the team organization for space image sensor design and production, the latest results of a high performances 512 X 512 pixels CMOS device characterization are presented with emphasis on the achieved electro-optical performance. Finally, the on going and short-term coming activities of the team are discussed.