Um importante diferencial competitivo das empresas distribuidoras de energia elétrica é a gestão da utilização dos seus ativos elétricos. Dentre eles destaca-se o transformador de potência em função de sua importância estratégica no fornecimento de energia aos grandes centros de carga. Para minimizar os impactos operacionais e sociais associados às interrupções constantemente monitoradas para que haja controle efetivo e garantia de funcionamento adequado e otimizado. O monitoramento das suas principais características é um ponto crítico que deve ser constantemente aprimorado, pela indiscutível importância destes ativos elétricos na continuidade do fornecimento de energia elétrica. Este trabalho apresenta proposta para avaliação em tempo real de falhas em transformadores de potência, para que sejam monitorados remotamente pela distribuidora, através do seu respectivo centro de operação do sistema elétrico, propiciando assertividade e rápida tomada de decisão gerencial em ocorrências de falhas internas, reduzindo os custos associados à interrupção do fornecimento de energia elétrica, diminuindo significativamente os tempos de restabelecimento do fornecimento e consequentemente minimizando impactos nos principais Indicadores de qualidade operacional da distribuidora. / An important competitive edge of electric power distribution companies is their electric assets utilization management. Among them stands outs the power transformers because of its strategic importance in the energy supply to high demand areas. To minimize operational and social impacts associated to the electric energy supply interruptions these equipments must to have their main characteristics constantly monitored to have effective control and optimizer functioning warranty. The main characteristics monitoring is a critical point which must be constantly improved, for the unquestionable importance of these electric assets in the electric energy supply continuity. This work shows a proposal to the real time power transformer failure, to remote monitoring by the utilities thru its respective electric system operation center, enabling assertively and fast management decision making in internal failure occurrences, reducing costs associated with electric energy supply interruption, decreasing the supply reestablishing times and consequently minimizing the impacts on the main distribution operational quality indicators.

Résumé indisponible / This PhD work is dedicated to investigate potentialities of phthalocyanines materials to realize a Quartz Crystal Microbalance (QCM) sensor for Benzene, Toluene and Xylenes (BTX) detection in air. The goal is to develop a sensor-microsystem capable of measuring BTX concentrations quantitatively below the environmental guidelines with sufficient accuracy. To achieve these objectives, our strategies mainly focused on experimental works encompassing sensors realization, sensing material characterizations, development of gas-testing facility and sensor testing for different target gases. One of the main aims is to identify most appropriate phthalocyanine material for sensor development. After comparative sensing studies, tert-butyl-copper phthalocyanine based QCM device is found as most sensitive and detail metrological characteristics are further investigated. Results show repeatable, reversible and high magnitude of response, low response and recovery times, sub-ppm range detection limit, high resolutions and combined selectivity of BTX gases among common atmospheric pollutants. Special focus is given to understand the gas/material interactions which are achieved by (a) XRD and SEM characterizations of sensing layers, (b) formalization of a two-step adsorption model and (c) assessing extent of diffusion of target gas in sensing layer. At last, possible ageing of sensor and suitable storage conditions to prevent such effect are investigated.

Um importante diferencial competitivo das empresas distribuidoras de energia elétrica é a gestão da utilização dos seus ativos elétricos. Dentre eles destaca-se o transformador de potência em função de sua importância estratégica no fornecimento de energia aos grandes centros de carga. Para minimizar os impactos operacionais e sociais associados às interrupções constantemente monitoradas para que haja controle efetivo e garantia de funcionamento adequado e otimizado. O monitoramento das suas principais características é um ponto crítico que deve ser constantemente aprimorado, pela indiscutível importância destes ativos elétricos na continuidade do fornecimento de energia elétrica. Este trabalho apresenta proposta para avaliação em tempo real de falhas em transformadores de potência, para que sejam monitorados remotamente pela distribuidora, através do seu respectivo centro de operação do sistema elétrico, propiciando assertividade e rápida tomada de decisão gerencial em ocorrências de falhas internas, reduzindo os custos associados à interrupção do fornecimento de energia elétrica, diminuindo significativamente os tempos de restabelecimento do fornecimento e consequentemente minimizando impactos nos principais Indicadores de qualidade operacional da distribuidora. / An important competitive edge of electric power distribution companies is their electric assets utilization management. Among them stands outs the power transformers because of its strategic importance in the energy supply to high demand areas. To minimize operational and social impacts associated to the electric energy supply interruptions these equipments must to have their main characteristics constantly monitored to have effective control and optimizer functioning warranty. The main characteristics monitoring is a critical point which must be constantly improved, for the unquestionable importance of these electric assets in the electric energy supply continuity. This work shows a proposal to the real time power transformer failure, to remote monitoring by the utilities thru its respective electric system operation center, enabling assertively and fast management decision making in internal failure occurrences, reducing costs associated with electric energy supply interruption, decreasing the supply reestablishing times and consequently minimizing the impacts on the main distribution operational quality indicators.

Today there is a great deal of interest in the development of gas sensors for various applications like monitoring of toxic gases, detection in oil reservoirs, mines, homes etc. Solid-state gas sensors have many advantages over the conventional analytical methods and hence are widely used. Amongst them, semiconducting metal-oxides based sensors are popular due to many advantages like low cost, small size, high sensitivity and long life. The present thesis reports a detailed work of TiO2 (Titania) thin film fabrication based on sol-gel method, study of their crystallization behavior and surface morphology, and characterizing them for alcohol sensing properties Sol-gel method is a wet chemical technique with many advantages over the conventional methods and offers a high degree of versatility to modify the film properties. Titania thin films were made with titanium isopropoxide as the precursor and ethanol and isopropanol as the solvents. Also effect of surfactants(PEG and CTAB) on the sol properties and film properties have experimentally examined. A in-house gas sensor testing setup has been designed and fabricated to characterize the sensors. Sensors with three different electrode configurations and also two different electrode material have been tested. The electrode geometry and material play a significant role on the sensing behavior and results for the same have been discussed.

Au cours des dernières années, les efforts de recherche et de développement pour les capteurs de gaz se sont orientés vers l'intégration de nanomatériaux afin d'améliorer les performances des dispositifs. Ces nouvelles générations promettent de nombreux avantages notamment en matière de miniaturisation et de réduction de la consommation énergétique. Par ailleurs, la détection sous gaz (sensibilité, seuil de détection, temps de réponse, ...) s'en retrouve améliorée à cause de l'augmentation du ratio surface/volume de la partie sensible. Ainsi, de tels capteurs peuvent être intégrés dans des systèmes de détections ultrasensibles, autonomes, compactes et transportables. Dans cette thèse, nous proposons d'utiliser des réseaux verticaux de nanofils semi-conducteurs pour créer des dispositifs de détection de gaz hautement sensibles, sélectifs, avec une faible limite de détection (de l'ordre du ppb) et intégrable dans des technologies CMOS, tout en étant générique et adaptable à plusieurs types de matériaux afin de discriminer plusieurs gaz. Une première partie expose la mise au point d'un procédé grande échelle, reproductible, compatible avec l'industrie actuelle des semi-conducteurs (CMOS), pour obtenir un capteur basé sur une architecture 3D à nanofils. Le dispositif est composé de deux contacts symétriques en aluminium à chaque extrémité des nanofils, dont l'un est obtenu par l'approche dite du " pont à air ", permettant la définition d'un contact tridimensionnel au sommet du nanofil. La seconde partie présente les performances sous gaz des dispositifs développés et les mécanismes de fonctionnement. Le capteur démontre des performances record en matière de détection du dioxyde d'azote (30% à 50 ppb) en comparaison à l'état de l'art (25% à 200 ppb). De plus, cette approche permet de mesurer de très faibles concentrations de ce gaz (< 1 ppb) de manière sélective, dans des conditions proches des conditions réelles : humidité (testé jusqu'à 70% d'humidité) et mélange avec d'autres gaz plus concentrés et la réversibilité du capteur est naturelle et se fait à température ambiante sans nécessité des conditions particulières. / In recent years, efforts of research and development for gas sensors converged to use nanomaterials to optimize performance. This new generation promises many advantages especially in miniaturization and reduction of energy consumption. Furthermore, the gas detection parameters (sensitivity, detection limit, response time ...) are improved due to the high surface/volume ratio of the sensitive part. Thus, this sensors can be integrated in ultrasensitive detection systems, autonomous, compact and transportable. In this thesis, we propose to use 3D semiconductor nanowires networks to create highly sensitive and selective gas sensors. The objective of this work is to provide a highly sensitive sensor, featuring a low detection limit (in the ppb range) and embeddable in CMOS devices. In addition process is generic and adaptable to many types of materials to discriminate several gas and converge to electronic nose. The first part of the dissertation is based on development of a large scale, reproducible, compatible with Si processing industry and conventional tools (CMOS), to obtain a sensor based on a 3D nanowire architecture. The device is composed by two symmetrical aluminum contacts at each extremity of the nanowires, including a top contact done by air bridge approach. The second part of this work presents the gas performances of components and working mechanisms associated. A very high response (30%) is obtained at 50 ppb of NO2, compare to the state of the art, 25% reached for 200 ppb. This approach can measure selectively very low concentrations of gas (<1 ppb) in real working conditions: moisture (tested up to 70% moisture) and mixing with other more concentrated gas (interfering gas). In addition, the reversibility of the sensor is natural and occurs at room temperature without requiring specific conditions.

Des matériaux hybrides de classe II ont été préparés à partir de précurseurs bis(tripropynylstannylés). Deux familles de précurseurs sol-gel incluant des espaceurs hydrocarbonés et thiophénique ont été obtenues et conduisent à des matériaux hybrides auto-organisés où les plans d’oxyde sont séparés par les espaceurs organiques. Ainsi l’espaceur rigide a donné lieu à une structure pseudo-lamellaire montrant une bande d’émission monomère avec un assez faible décalage vers le rouge par rapport à l'émission des précurseurs en solution. En revanche, alors que les xérogels thiényle plus désordonnés conduisent à une large émission caractéristique de la formation d’excimères ou de dimères. Par ailleurs, des films minces contenant les espaceurs alkylène et arylalkylène ont été préparés et ont montré une morphologie "pseudoparticulaire" poreuse et un ordre à courte distance contenant des réseaux SnOx. De façon inattendue, ces films minces hybrides détectent le dihydrogène dès une température de 50 °C dans la gamme 200-10000 ppm. A partir de ces films hybrides minces, le dioxyde d'étain cristallin (SnO2) a été préparé par un post-traitement thermique. Comme prévu, ces films SnO2 cassitérite détectent le dihydrogène et, dans une moindre mesure le monoxyde de carbone avec une température optimale de fonctionnement comprise entre 300 et 350 °C. / Class II hybrid materials were prepared from ditin hexaalkynides. Two families of precursors, including either hydrocarbon or oligothiophene-based spacers, were obtained and led by the sol-gel process to self-assembled organotin-based hybrid materials made of planes of oxide separated by organic bridges. Thus, the rigid thienyl spacer gave rise to a “pseudo-lamellar” structure that showed a monomer emission band with a rather small red-shift compared with to the emission of the precursor in solution. However more disordered thienyl xerogels led to broad emission features assigned to excimer or dimer formation. Moreover, thin films containing alkylene- and arylalkylene bridged have been prepared and showed a “pseudoparticulate” porous morphology and a short-range hierarchical order in the organic-inorganic SnOx pseudoparticles. Unexpectedly these hybrid thin films detect hydrogen gas at a temperature as low as 50 °C at the 200-10000 ppm level. From these hybrid thin films, crystalline tin dioxide (SnO2) were prepared by a thermal post-treatment. As expected, cassiterite SnO2 films detected H2 and to a less extent CO with a best operating temperature comprised between 300 and 350 °C.

Yttria stabilized Zirconia (8YSZ) is an extensively used solid electrolyte, which finds applications in electrochemical sensors, solid oxide fuel cells and gate oxide in MOSFETs. Recent studies report that YSZ thin films are better performers than their bulk counterparts, in terms of ionic conductivity even at moderate temperatures. YSZ thin films also attract attention with the scope of device miniaturization. However, most of the studies available in the literature on YSZ thin films focus mainly on their electrical characterization. In this work, YSZ thin films were deposited, characterized and possible use of sensors were evaluated. In the present work, 8 mol% yttria stabilized zirconia thin films were deposited using RF magnetron reactive sputtering under different deposition conditions. Films with thicknesses ranging from few tens to few hundreds of nanometres were deposited. The deposited films were subjected to morphological, structural, compositional and electrical characterizations. Deposition and annealing conditions were optimized to obtain dense, stoichiometric and crystalline YSZ thin films. The ionic conductivity of 200 nm nanocrystal line thin film was found to be two orders of magnitude higher than the bulk. The ionic conductivity increased with the decrease in film thickness. Compositional analyses of a set of YSZ thin films revealed free surface yttrium segregation. The free surface segregation of dopants can locally alter the surface chemistry and influence the oxygen transfer kinetics across the electrode-electrolyte interface. Although number of reports are available on the segregation characteristics in YSZ bulk, no reports are available on yttria segregation in YSZ thin film. Hence, this work reports detailed investigations on the free surface yttria segregation in YSZ thin films using angle resolved X-ray photoelectron spectroscopy (XPS). Influence of annealing temperature, film thickness, annealing time, and purity on the segregation concentration was determined. It was found that the most important factor that determines the segregation was found to be the target purity. The segregation depth profile analysis showed that the segregation layer depth was proportional to segregation concentration. Free surface segregation reduced the ionic conductivity of the YSZ thin films roughly about a factor. However, segregation did not affect the film’s morphology, grain size, crystallinity and activation energy. The difference in ionic conductivity observed in the segregated and clean YSZ films suggests that dopant free surface segregation could also be one of the reasons for the variable ionic conductivity reported in the literature. For using YSZ in miniaturized devices, micro-structuring of YSZ is important. It has been reported that the wet etching techniques available for YSZ were not repeatable and do not etch annealed YSZ samples. Reactive ion etching (RIE) is better suited for YSZ patterning due to its capability to offer high resolution, easy control and tenable anisotropic/isotropic pattern transfer for batch processing. Although reports are available on the dry etching of zirconia and yttria thin films, no studies were reported on the dry etching of YSZ thin films. In this work, inductively coupled reactive ion etching (ICP-RIE) using fluorine and chlorine chemistries were employed to etch YSZ thin films. Optimized etching conditions were identified by varying different process parameters like, type of gas, gas flow rate, RF power, ICP power, chamber pressure and carrier wafer in the ICP-RIE process. Optimized conditions were chosen by examining the etch depth, composition analyses before and after etch using XPS, selectivity towards SiO2 (which is the most common buffer layer) and surface roughness. Etch chemistries involved in a particular plasma (SF6, Cl2 and BCl3) were discussed with the help of surface composition and etch thicknesses. The results showed that etching YSZ with BCl3 plasma at optimized conditions yielded best results through oxygen-scavenging mechanism. A maximum etch rate of 53 nm/min was obtained in BCl3 plasma using PECVD Si3N4 carrier wafer at an ICP power of 1500 W, RF power of 100 W, chamber pressure of 5 mTorr with 30 sccm BCl3 flow. Sensing devices were designed by employing YSZ thin film as solid electrolyte and nickel oxide and gold thin film as sensing and reference electrodes, respectively to evaluate the possible use of YSZ thin film in miniaturized NO2 sensor. The electrodes were deposited in inter-digitated pattern. Two types of electrodes were designed with different number of fingers in symmetric and asymmetric configurations. The NO2 sensing was performed in the concentration range of 25 to 2000 ppm at three different temperatures, 673, 773 and 873 K in mixed potential and impedance metric modes. The mixed potential type measurements were carried out only for asymmetric cell in two different electrode configurations. The impedance metric type measurements were carried out for both symmetric and asymmetric cells in two different electrode configurations. Preliminary NO2 sensing experiments in both the types of measurements revealed that in devices with electrodes having more fingers were better in performance. In mixed potential type sensors, sensitivity was measured as the amount of voltage generated when the sensor was exposed to a test gas. The generated voltage was found to be proportional to the logarithm of NO2 concentration in the entire measurement range (50 to 2000 ppm) with the regression fitting parameter, adj.R2 around 0.97 to 0.99 in all the cases. A maximum potential of 271 mV was measured with 2000 ppm NO2 at 873 K. The response and recovery times of the sensors were sensitive to the operating temperature. In impedance metric mode, the sensitivities were measured as the variation in the low frequency phase angle (∆ φ) when the gas concentration is changed. The frequency range of the measurement was from 0.01 Hz to100 kHz. The response time in the impedance metric sensors was comparable to that of mixed potential sensors. But the recovery time in impedance metric sensors was much was slower than the mixed potential type for all the concentrations. The sensors showed linear response only in a narrow range of 50 to 500 ppm with regression fitting value, R2 around 0.98 in all the cases. Above 500 ppm, the sensitivity value was observed to be saturated. From the gas sensing studies performed on the miniaturized sensors, it was found that the mixed potential type sensing mode is better than the impedance metric type in YSZ thin film based devices. However detailed interference gas studies were needed before drawing any conclusion. In summary, the studies presented in the work have contributed to the understanding of free surface yttria segregation behaviour in YSZ thin films. Micromachining conditions were optimized for both pristine and annealed YSZ thin films. Suitability of YSZ thin film based miniaturized NO2 gas sensor was evaluated.

Ce travail nous a permis de réaliser une étude de capteurs de gaz et d’humidité à base de graphène. Cette étude pourrait être utile non seulement pour améliorer les performances des capteurs à base de graphène mais aussi pour mieux comprendre l’interaction entre le graphène et les molécules de gaz. Ceci semble indispensable pour faire avancer les applications du graphène comme un matériau prometteur pour la détection des gaz. Des avancées significatives ont été présentées au niveau de la fabrication de ces capteurs, leurs différentes caractérisations électriques ainsi que d’autres techniques employées pour analyser le mécanisme contrôlant la détection des molécules de gaz/vapeur. Ces outils ont été mis en place pour concevoir et fabriquer plusieurs structures de capteur en utilisant différents substrats support du graphène d’une part et en modifiant les propriétés du graphène par utilisation des produits chimiques d’autres part. La caractérisation de ces capteurs sous différents environnements a permis de comparer les différentes réponses des capteurs et d’en tirer plusieurs conclusions sur le fonctionnement de ces dispositifs. En effet, le Mica, un substrat lisse et transparent, a été utilisé comme substrat pour le graphène. Le dopage induit par le mica a été étudié ainsi que son impact sur la sensibilité du graphène au gaz d’ammoniac. Ceci a permis de mettre en évidence le fait que le substrat joue un rôle important pour la détection de l’ammoniac. De plus, ces capteurs fabriques sur mica et SiO2 ont été testés sous différentes conditions de températures et d’oxygène. Dans une autre approche, un polymère a été utilisé pour doper le graphène. Une étude détaillée a été menée pour analyser le comportement de ce graphène fonctionnalisé par rapport aux molécules d’eau. Ces nouveaux résultats expérimentaux obtenus pendant cette thèse constituent un bon support à plusieurs résultats théoriques établis et permettent d’optimiser la conception des capteurs de gaz à base de graphène pour des meilleures performances. / In this research, we report on a study of graphene based gas and humidity sensors. This study could be useful not only to improve the performance of graphene based sensors but also to better understand the interaction between graphene and gas molecules. This seems necessary to promote the applications of graphene as a promising material for gas sensing. Significant advances have been made to design and fabricate these sensors: the different electrical characterizations as well as other techniques used to analyze the mechanism controlling the detection of gas/vapor molecules. These tools have been set up to design and manufacture various sensor structures using different underlying substrates for graphene on one hand and chemical modification of graphene properties on the other hand. The characterization of these sensors under different environments was used to compare the different responses of the sensors and draw several conclusions about gas sensing mechanism. Indeed, Mica, a smooth and transparent substrate, was used as a supporting substrate for graphene. Doping induced to graphene by mica and its impact on graphene sensitivity to ammonia gas were studied. This has made it possible to highlight the fact that the substrate plays an important role for the detection of ammonia. In addition, these sensors made on mica and SiO2 were tested under a variety of temperatures and oxygen. In another approach, a polymer was used to dope graphene. A detailed study was realized about the behavior of water molecules on functionalized graphene. The obtained experimental results, reported for the first time, represent a good support for several theoretical studies already made and could be used to optimize the design of graphene based gas sensors.

Il est reconnu que la structure des semi-conducteurs organiques influence la sensibilité et la sensitivité des capteurs des gaz. Pour améliorer la compréhension des mécanismes sous-jacents dans les capteurs à base des transistors d’effet de champ organique (OFETs) cette thèse a exploré trois pistes différentes : L’utilisation de l’hystérésis des caractéristiques de transfert comme paramètre de détection des gaz est étudié. En ajoutant l’hystérésis aux paramètres standards, on améliore la sélectivité des OFETs à base de poly(3-hexylthiophène) aux gaz polaires. Des mesures transitoires de courant indiquent que la cinétique de piégeage et de piégeage des porteurs de charges est à l’origine de cette amélioration. Pour comprendre l’influence qu’à la structure moléculaire sur la sensibilité aux vapeurs d’éthanol, des polymères avec des chaînes latérales alcoxyle dont on fait varier la polarité ainsi que l’encombrement stérique, ont été étudiés. L’intensité de la réponse est corrélée avec la quantité d’analyte absorbée et le moment dipolaire des chaînes latérales. Pour permettre l’étude des mécanismes à l’échelle nanométrique, une partie de ce travail se concentre sur la fabrication de transistors avec une taille de canal réduite. En utilisant le nitrure de silicium comme couche diélectrique, on réduite les tensions de commande et les propriétés chimiques à l’interface. / The molecular structure of organic semiconductors which can be tailored by the chemical synthesis influences the sensitivity and selectivity of gas sensor devices. To improve the understanding of the ongoing mechanisms in sensors based on organic field effect transistors (OFETs) this thesis follows three different tracks: The applicability of the hysteresis of the transfer characteristics as a gas sensing parameter is studied. As a complement to the standard transistor parameters the hysteresis improves the selectivity of poly(3-hexylthiophen-2,5-diyl) based OFETs to polar gases. Transient current measurements indicate the additional dependence on the detrapping kinetics as origin of the increased selectivity. To understand the influence of the molecular structure on the gas sensing behavior, polymers with alkoxy side chains, varying in polarity and steric hindrance, are used as gas sensing layer for ethanol vapor. The response strength correlates with the amount of absorbed analyte and the dipole moment of the side chains. To enable investigations of the mechanisms at the nanoscale, one part of this work focuses on the preparation of transistors with a reduced channel length. By using silicon nitride as dielectric layer, driving voltages decreased and interface properties could be improved.

L’objectif de cette étude était d’obtenir un capteur à bas coût, fonctionnant à température ambiante, et permettant d’obtenir une information sur la concentration d’ammoniac d’une atmosphère, sans tenir compte de l’humidité. Cela implique une très faible sensibilité à l’humidité et une faible synergie entre l’eau et l’ammoniac.Au terme d’une étude sur la mise en forme de films hybrides hydrophiles, par un procédé « propre » dans l’eau, un capteur a été développé, par un assemblage en couche par couche de polyélectrolytes hydrophiles, la polyaniline et la phtalocyanine tétrasulfonée de cuivre : PANI/TsPcCu. Ce capteur présente une limite de détection d’ammoniac inférieure au ppm et une très faible sensibilité à l’eau, permettant de détecter l’ammoniac sans informations sur l’humidité de l’air.De nouveaux dispositifs, basés sur un mode de transduction breveté, ont été étudiés : les heterojonctions MSDIs (Molecular Semiconductor-Doped Insulator). Ces dispositifs sont formés de deux couches superposées, une sous-couche isolante de type n, F16PcCu ou le PTCDA, et une couche supérieure semi-conductrice de type p, Pc2Lu. L’importance de la jonction entre les deux matériaux, mais aussi de la jonction entre les électrodes et la sous-couche, a été démontrée à l’aide de mesures d’impédances. Les propriétés capteurs des dispositifs MSDI ont été étudiées par exposition à l’ammoniac sur une large gamme d’humidité. Ils présentent une très faible sensibilité à l’eau et permettent de détecter des concentrations d’ammoniac inférieures au ppm. Suite au développement d’un banc de mesures spécifique permettant l’affinage de fromages, celui-ci a pu être suivi par des mesures capteur avec un résistor de PcCo et par GC-MS. Ces mesures ont mis en évidence l’intérêt de tels capteurs pour suivre l’évolution de la maturation des fromages. / The aim of this study was to obtain a low cost sensor, working at room temperature, capable to obtain an information about the ammonia concentration without any information about the humidity. These characteristics imply a very low sensitivity to humidity and a low cross sensitivity between humidity and ammonia.After a study on material processing of hydrophilic films using water as solvent, a sensors has been developed by using layer by layer assembly of polyelectrolytes, such as polyaniline and the tetrasulfonated copper phthalocyanine: PANI/TsCuPc. This sensor is able to detect sub ppm ammonia concentration, with a very low cross sensitivity between ammonia and water which allow ammonia sensing without any information about the humidity.New devices based on a patented transduction method were studied: the MSDIs heterojunctions (Molecular Semiconductor-Doped Insulator). This kind of device is prepared with two different layers, a sub layer of an n-type insulator, F16CuPc or PTCDA, and an upper layer of a p-type semiconductor, LuPc2. The importance of the junction between both materials and between the sub layer and the electrodes were studied by using ammonia exposure on a large humidity range. They exhibit a very low sensitivity to humidity and allow sub ppm ammonia sensing whatever the humidity is.A specific workbench has been developed and tested in the laboratory, to follow cheese ripening by using CoPc gas sensors and gas chromatography. These measurements showed readiness to the use of the kind of gas sensors for the follow up of dairy products.