Laurent Rubaldo was born in France in 1975. He received his engineering diploma from INSA Toulouse in 1997, his Ph.D. in Physics from the University Grenoble Alpes (formerly University Joseph Fourier of Grenoble) in 2001, and his Habilitation to supervise research from the same university in 2019. He joined STMicroelectronics in 2001, first as an R&D engineer for device characterisation, and moved to a position of technical leader for process development. In 2007, he joined LYNRED (formerly Sofradir Group) as R&D engineer to work on the electro-optical characterisation and performance optimisation of cooled IR photodetectors. Since 2017, he has held the position of Senior Expert in semiconductor and optoelectronic technologies. Involved in academic and research partner networks, he is coordinator of the DEFIR joint laboratory with CEA-Leti and vice-director of the DECID joint laboratory with CROMA-CNRS since 2021. Member of the Grenoble-INP UGA and Fondation Grenoble INP boards, he is chairman of the board of the Phelma engineering school since 2021.
He is the author of seven patents and more than one hundred scientific articles. He has supervised 8 doctoral theses.
He is the author of seven patents and more than one hundred scientific articles. He has supervised 8 doctoral theses.
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We review the latest developments at LYNRED on III-V technologies, in terms of operability, residual fixed pattern noise (RFPN) and Modulation Transfer Function (MTF) optimizations.
Among these next generations technologies, Campus will serve the ongoing developments of sub-10μm pitch cooled infrared detectors, MCT HOT technology, for extended MW band and III-V HOT MW blue band technology.
We will discuss in this paper the true figures of merit that have to be addressed during technology development and optimization to meet field mission requirements. We will then review latest results on II-VI and III-V HOT IDDCA (Integrated Detector Dewar Cryocooler Assembly) with 7.5μm pitch SXGA format focal plane array in terms of low frequency noise defects, stability and reproducibility of residual fixed pattern noise (RFPN) and Modulation Transfer Function (MTF) optimizations while maintaining high quantum efficiency to keep highest possible range.
CAGIRE is the near infrared camera of the Colibrí robotic telescope, designed for the follow-up of SVOM alerts, mainly Gamma Ray Bursts (GRBs), and the quick imaging of sky regions where transient sources are detected by the SVOM satellite. CAGIRE is based on the Astronomical Large Format Array (ALFA) 2k x 2k SWIR sensor from the French consortium CEA-LYNRED. In the context of CAGIRE the sensor is operated in “Up the Ramp” mode to observe the sky in a square field of view of 21.7 arcmin on a side, in the range of wavelengths from 1.1 to 1.8 μm. An observation with CAGIRE consists of a series of short (1-2 minutes) exposures during which the pixels are read out every 1.3 second, continuously accumulating charges proportionally to the received flux, building a ramp.
The main challenge is to quickly process and analyse these ramps, in order to identify and study the near infrared counterparts of the bursts, within 5 minutes of the reception of an alert. Our preprocessing, which is under development, aims at providing reliable flux maps for the astronomy pipeline. It is based on a sequence of operations. First, calibration maps are used to identify saturated pixels, and for each pixel, the usable (non saturated) range of the ramp. Then, the ramps are corrected for the electronic common mode noise, and differential ramps are constructed. Finally, the flux is calculated from the differential ramps, using a previously calibrated map of pixel non-linearities. We present here the sequence of operations performed by the preprocessing, which are based on previous calibrations of the sensor response. These operations lead to the production of a flux map corrected from cosmic-rays hits, a map depicting the quality of the fit, a map of saturated pixels and a map of pixels hit by cosmic-rays, before the acquisition of the next ramp. These maps will be used by the astronomy pipeline to quickly extract the scientific results of the observations, like the identification of uncatalogued or quickly variable sources that could be GRB afterglows.
On the other hand, these cutting edge performances are made possible thanks to Sofradir vertical industrial model. From the CdZnTe (CZT) and HgCdTe (MCT) crystal growth to the last electro-optical characterization recipe before shipping, and all the intermediate steps in between like IDDCA (Integrated Detector Dewar Cooler Assembly) final pumping cycle, all the manufacturing steps are developed, performed and controlled inhouse. This allows direct feedback between IDDCA, system performances and process or material. State of the art relevant performances for IR detection and imaging will be presented, that is to say low excess noise defects, RFPN (Residual Fixed Pattern Noise), NUC (Non Uniformity Correction) table stability for Daphnis product, 10μm pitch XGA extended MW matrix at 110K and HOT (High Operating Temperature) p-on-n technology, VGA format with 15μm pitch MW at 160K.
The p on n technology is based on an In doped absorbing material and an As implanted junction area. This architecture allows decreasing both dark current and series resistance compared to the legacy n on p technology based on Hg vacancies. This technology demonstrated an operating temperature up to 100K and a typical operability over 99.5%.
Some applications require a lower dark current in the range 90K to 110K, a lower average noise level and a lower number of noise defects than the present ones. In order to address these specific requirements, Sofradir performed some technological improvements.
In this paper, the technological improvements are briefly described. These technological tunings led to a 40% decrease of dark current at 110K. Both noise level and number of noise defects are kept constant in the range 90K to 110K. These improvements are paving the way to a further increase of operating temperature for long wave (LW) devices.
RMS noise modeling and detection for high-reliability HgCdTe infrared focal plane arrays development
Sofradir was first to show a 10μm focal plane array (FPA) in DSS 2012, and announced the DAPHNIS 10μm product family back in 2014. This pixel pitch is key for enabling more compact sensors and increased resolution. SOFRADIR recently achieved outstanding MTF demonstration at this pixel pitch, which clearly demonstrate the benefit to users of adopting 10μm pixel pitch focal plane array based detectors. The last results, and associated gain in detection performance, are discussed in this paper.
Concurrently to pitch downsizing, SOFRADIR also works on a global offer using digital interfaces and smart pixel functionalities. This opens the road to enhanced functionalities such as improved image quality, higher frame rate, lower power consumption and optimum operation for wide thermal conditions scenes. This paper also discusses these enhanced features and strategies allowing easier integration of the detector in the system.
In parallel we have been pursuing further infrared developments on future MWIR detectors, such as the VGA format HOT detector that consumes 2W and the 10μm pitch IR detector which gives us a leading position in innovation. These detectors are designed for long-range surveillance equipment, commander or gunner sights, ground-to-ground missile launchers and other applications that require higher resolution and sensitivity to improve reconnaissance and target identification. This paper discusses the system level performance in each detector type.
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