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Conception, modélisation et caractérisation de détecteurs microbolométriques pour l’imagerie sub-terahertz

Abstract : This PhD dissertation presents the analysis, characterization and optimization of the performances of microbolometric imagers in the sub-THz frequency range. This non ionizing span of the electromagnetic spectrum is currently a booming field of research. Development of high-performance and room temperature imagers, opens the path towards many applications. One of such promising application is non-destructive screening enabled by the good penetrating power of these radiations through many materials, especially at frequencies lower than 1 THz. Through a radiometric analysis of an active imaging system, we assess the required performances of an imager suited for this application.In this context, we have analyzed the electrothermal performances of the cutting-edge THz imagers based on microbolometer developed at CEA-Leti. Thanks to a detailed model of the bolometer bridge of these detection arrays, we have brought into focus the limiting factors of the current devices. Technological improvement have been considered such as the integration of a new thermometer material. The performance improvements brought by these optimizations have been quantified thanks to the modeling tool we have developed and it is showed that sensitivity close to the pW range can be reached on these imagers.An intensive experimental work have also been carried out in order to assess the sub-THz electromagnetic performances of the microbolometer antenna structure. Particular emphasis was placed on the metrology of the optical bench that has been built, aiming at the precise measurement of the figure of merit of the detectors. These experimental results have validated the electromagnetic simulations of the detector absorption efficiency that have exposed the coupling with the CMOS circuitry that arises at low frequencies. The consequences of this coupling on the quality of an imaging system using this detection array has been estimated. Modulation Transfer Function of the pixel has been quantified and the impact on the system resolution estimated.In order to improve the absorption efficiency of the detectors measured in the sub-THz range, we have studied the integration of high impedance surfaces within the microbolometer stack. The sizing of the high impedance surfaces has been carried out with metamodeling, leading to optimal designs with a limited number of full-wave simulations. New pixel architectures that are compatible with current imagers have been investigated. Simulations demonstrated that peak absorption efficiency higher than 60 % can be reached at 670 GHz despite a 50 µm pixel pitch, much smaller than targeted wavelength. Finally, compactness and efficiency of the high impedance surfaces have been improved by particular swarm optimization algorithm that have been specifically developed.
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https://tel.archives-ouvertes.fr/tel-01829740
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Submitted on : Wednesday, July 4, 2018 - 12:00:07 PM
Last modification on : Monday, October 19, 2020 - 11:09:48 AM
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MEILHAN_2017_diffusion.pdf
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  • HAL Id : tel-01829740, version 1

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Jérôme Meilhan. Conception, modélisation et caractérisation de détecteurs microbolométriques pour l’imagerie sub-terahertz. Optique / photonique. Université Grenoble Alpes, 2017. Français. ⟨NNT : 2017GREAT114⟩. ⟨tel-01829740⟩

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