Integrated SOI photoacoustic gas sensor at THz frequencies for food quality control application ; Capteur à gaz intégrée sur SOI pour la détéction photoacoustique aux fréquences THz, appliqué au contrôle de qualité alimentaire

In this thesis work, a photoacoustic THz gas sensor (operating in the 620-690 GHz band) used for monitoring Volatile Organic compounds (VOCs) in food packages is presented. This gas sensor is fabricated on low-loss THz High resistivity Silicon (HR-Si) waveguides. The design, modal analysis, and propagation losses of the suspended Si waveguide are discussed in detail. Highly competitive losses not exceeding 0.6 dB/cm in this band have been measured. Three different resonators: photonic, acoustic, and mechanical are at the origin of the gas sensor designs. They allow to triply enhance the detected photoacoustic signal and to reduce the minimum detection limit of the gas sensor. Photonic crystal (PhC) cavities representing the THz photonic resonator are created on top of the Si waveguide. The design optimization and experimental characterizations of several THz PhC cavities are presented in this work. This has led to a resonant PhC cavity at 640 GHz with a record Q factor of 18000. A central hole of the PhC cavity behaves as an acoustical resonator. It is covered by a stressed polycrystalline silicon (Poly-Si) membrane that corresponds to the mechanical resonator. Analytical analysis and experimental characterization measurements are performed to study these acousto-mechanical resonators. The combination of the above realizations has allowed us to demonstrate the first THz photoacoustic detection of low concentrations (200 ppm) of H2S molecules on an integratable platform. H2S being a crucial indicator of food spoilage, this work is therefore an important first step towards a real time compact sensor technology, both for food quality control applications as well as environmental and biomedical ones. ; Ce travail de thèse présente un capteur de gaz photoacoustique aux fréquences THz utilisé pour surveiller les composés organiques volatils (COV) dans les emballages alimentaires. Ce capteur de gaz est fabriqué sur un guide d'onde THz à faible perte en silicium à haute résistivité (HR-Si). La conception, l'analyse ...