Lynred is leading the development of infrared detectors for high performances applications. Two trends are identified in the infrared range, the increase of the operating temperature and the pixel pitch reduction. For 15 years, the III-V technologies present an increasing interest to address both challenges. At LYNRED, these technologies allow to address Short Wave InfraRed (SWIR) and Mid-Wave InfraRed (MWIR) for ground applications. Many challenges have to be addressed for the future focal plane arrays (FPAs). Electrical and optical crosstalks as well as image quality and stability, are one of the prime concern for detectors with pixel pitch down to 7.5μm. In order to reach an industrial production level of infrared FPAs, technological developments are required at each steps: the epitaxy, the detector array process, flip chip and back end processing. Another key element is the Read Out Integrated Circuit (ROIC) designed in-house to fulfil our customer needs.
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.
LYNRED is a leading global provider of high-quality II-VI, III-V and bolometers infrared detectors for the aerospace, defence and commercial markets. Our vision is to preserve and protect, and provide the right technology to customers’ needs. To consolidate our position among infrared detector manufacturer leaders and to enable us to respond to growing market demand for next-generation infrared technologies, a new state of the art industrial facility is breaking ground. This new industrial site named Campus will double the current cleanroom footprint and increase production capacity with optimal cleanliness classification for new high-performance products.
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.
MCT p-on-n photodiodes manufactured at Lynred and CEA-LETI have demonstrated state of the art performances for HOT applications. On blue and red mid infrared bands on 15μm pixel pitch, respectively 150 and 130K operating temperatures have been obtained, due to diffusion limited dark current and low defectivity. To achieve equivalent results on smaller pixel, the p-on-n technology at DEFIR, joint laboratory between Lynred and CEA-LETI, has been improved. The technological process was modified to ensure a proper diode formation and to efficiently passivate the interface between MCT and encapsulation layers, especially in the vicinity of the space charge region. The manufactured arrays with a 5.3μm cutoff wavelength have been hybridized on a digital output SXGA (1280×1024) direct injection ROIC with a pixel pitch of 7.5 μm. This paper present the measured current, blackbody responsivity and RMS noise on FPAs with F/4 numerical aperture. We will also discuss spectral response, quantum efficiency, shot-noise limited photodiodes and noise histograms shapes and their distribution tails at 130K. The very low number of defective pixel allow to address higher operating temperature and measurements have been performed at 140K and even 150K with very limited performance degradation. Pixel pitch of 5 μm has been characterized on test chips and present I-V curves with low dispersion and long bias plateau. As for larger pixel sizes, these photodiodes are shot-noise limited. Modulation transfer function has been measured by electron beam induced current and presents high value, up to 56%.
LYNRED is oriented towards excellence in II-VI, III-V and bolometers technologies, covering all Society’s needs in term of infrared detection. Our vision is to preserve and protect, and more than ever, our goal is to provide the right technology to the field missions, spatial and industrial applications, and more generally the right technology to customers’ needs. For this purpose we are developing for the next generation pitch, MCT HOT technology, for extended MW band as well as III-V HOT MW blue band technology. Many challenges have to be addressed for future small pitch, large format and HOT detectors. Electrical and optical crosstalks as well as image quality and stability, are one of the prime concern for detectors with pixel pitch below 10μm. We will discuss about the trade-off between the different material properties and detector performances to ensure mandatory minimization of Minimum Resolvable Temperature Difference (MRTD) for range optimization. We will then review latest 7.5μm pitch development at LYNRED, with SXGA formats, based on II-VI and III-V HOT materials, in terms of operability, residual fixed pattern noise (RFPN) and Modulation Transfer Function (MTF) optimizations.
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