Dissertations / Theses on the topic 'MOX Gas sensor'

This thesis deals with one-dimensional (1D) and two-dimensional nanomaterials (2D) in terms of their utilization for new types of gas sensors. Thesis focuses on study of sensing elements for gas sensors based on semiconductor metal oxide materials (MOX) and their manufacturing technology. The objective of the thesis is the design and implementation of a sensing elements formed by selected nanomaterials based on the structure of interdigital electrodes. The result of the practical part of the thesis is the characterization and comparison of materials in terms of their detection parameters in the presence of selected test gases. The first part of thesis hierarchically defines chemoresistive gas sensor, characterizes and explains its operation principle. Second part studies 1D and 2D nanomaterials of sensing elements for MOX chemoresistive gas sensors, contains a research of their properties and describes their methods of manufacturing and implementation. The last part deals with the implementation of the sensitive layer of the sensor with selected nanomaterials, characterizes and compares their detection properties.

Il rilevamento di gas tossici e pericolosi è sempre stato necessario per motivi di sicurezza. Negli ultimi anni, in particolare, l’attenzione per lo sviluppo di sistemi portatili e a basso costo per il rilevamento dei gas è aumentata notevolmente. Questa tesi presenta circuiti CMOS versatili, veloci, ad alta precisione e basso consumo per applicazioni portatili di rilevamento di gas. I sensori target sono i Metal Oxide Semiconductor (MOX). Questi sensori sono ampiamente utilizzati per la loro intrinseca compatibilità con le tecnologie MEMS integrate. Le tipologie di lettura scelte sono basate su un oscillatore controllato dalla resistenza del sensore stessa, in modo da ottenere una conversione resistenza-tempo. Ciò garantisce un ampio range dinamico, una buona precisione e la capacità di far fronte alle grandi variazioni di resistenza del sensore MOX. Quattro diversi prototipi sono stati sviluppati e testati con successo. Sono state anche eseguite misurazioni chimiche con un vero sensore SnO2 MOX, validando i risultati ottenuti. Le misure hanno mostrato come il sensore e l’interfaccia sia in grado di rilevare fino a 5ppm di CO in aria. Gli ASIC sono in grado di coprire 128 dB di DR a 4Hz di output data rate digitale, o 148 dB a 0.4Hz, garantendo un errore relativo percentuale sempre migliore dello 0,4% (SNDR> 48 dB). Le prestazioni target sono state raggiunte con aggressive strategie di progettazione e ottimizzazione a livello di sistema. È stata utilizzata una tecnologia CMOS a 130nm fornita da Infineon Technologies AG. La scelta di un nodo tecnologico così scalato (rispetto alle tipiche implementazioni in questo settore) ha consentito di ridurre ulteriormente i consumi fino a circa 450 μA. Inoltre, questo lavoro introduce la possibilità di utilizzare la stessa architettura basata su oscillatore per eseguire la lettura di sensori capacitivi. I risultati delle misurazioni con sensori capacitivi MEMS hanno mostrato 116 dB di DR, con un SNR di 74 dB a 10Hz di velocità di trasmissione dati digitale. Le architetture sviluppate in questa tesi sono compatibili con gli standard moderni nel settore del rilevamento del gas per dispositivi portatili.
Detection of toxic and dangerous gases has always been a need for safety purpose and, in recent years, portable and low-cost gas sensing systems are becoming of main interest. This thesis presents fast, high precision, low-power, versatile CMOS interface circuits for portable gas sensing applications. The target sensors are Metal Oxide Semiconductor (MOX) sensors which are widely used due to their inherent compatibility with integrated MEMS technologies. The chosen readout typologies are based on the time-domain Resistor-Controlled Oscillator. This guarantees wide dynamic range, good precision and the ability to cope with the large MOX sensor resistance variations. Four different prototypes have been successfully developed and tested. Chemical measurements with a real SnO2 MOX sensor have also been performed to validate the results, showing a minimum CO detection capability in ambient air of 5 ppm. The ASICs are able to cover 128 dB of DR at 4 Hz of digital output data rate, or 148 dB at 0.4 Hz, while providing a relative error always better than 0.4% (SNDR >48 dB). Target performances have been achieved with aggressive design strategies and system-level optimization, and using a scaled (compared to typical implementations in this field) 130nm CMOS technology provided by Infineon Technologies AG. Power consumption is about 450 μA. Moreover, this work introduces the possibility to use the same oscillator-based architecture to perform capacitive sensors readout. Measurement results with capacitive MEMS sensors have shown 116 dB of DR in CSENS mode, with an SNR of 74 dB at 10 Hz of digital output data rate. The architectures developed in this thesis are compatible with the modern standards in the portable gas sensing industry.

Despite advantages highlighted by Metal OXides (MOX) based gas sensors, these devices still present drawbacks in their performances (e.g. selectivity, stability and high operating temperature), so further investigations are necessary. Researchers tried to address these problems in several ways, which includes new synthesis methods for innovative materials based on MOX, such as solid solutions, addition of catalysts and doping of MOX by using external atoms or oxygen vacancies. Concerning this last issue, literature presents a lack of studies on how the arrangement and number of oxygen vacancies affect the sensing performance and only a few preliminary works highlighted interesting results. Another way to overcome MOX sensor drawbacks is to investigate novel class of materials, such as metal organic framework or 2D materials. Among these, phosphorene is one of the best candidates for such technological application, since it shows a chemoresistive activity at room temperature. The goal of this work is to decrease the operating temperature of SnO2 based gas sensors by exploiting the oxygen vacancies. First, a theoretical investigation was done in the framework of Density Functional Theory (DFT) to investigate, on the atomic scale, how oxygen vacancies influence the physical and chemical properties of the material. The effect of oxygen vacancies on the structural, electronic and electrical properties of bulk SnO2 at two different concentrations was studied, then the formation of surface oxygen vacancies was investigated in order to study the adsorption of oxygen molecules from the surrounding atmosphere on the stoichiometric and reduced SnO2 surface. Then, reduced SnO2-x was synthesized and devices based on the produced material were fabricated and tested. The results showed a high response of the sensors towards low concentrations of nitrogen dioxide NO2 (500 ppb) at 130°C instead of the typical operating temperature of 450°C for SnO2-based gas sensors. This decrease in the operating temperature results in a decrease of the power consumption of the device, opening up to its possible employment on portable devices like mobile phones. The results were interpreted characterizing the material by mean of X-ray Powder Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscope (SEM) and Ultraviolet–visible spectroscopy (UV-visible) analysis. In the end, the experimental results were compared to the DFT outputs obtained. As mentioned before, phosphorene is one of the promising 2D materials for gas sensing applications, but it still presents some drawbacks, mainly due to the material degradation over the time when exposed to ambient conditions. Many investigations were done on decorating phosphorene with metal atoms in order to enhance its performance for different technological applications. Nickel is one of metals proposed for such purpose, but few studies were done on nickel decorated phosphorene for gas sensing applications, especially for gas sensing application. In the innovative work here proposed, DFT calculations were carried out to explain how nickel influences the electronic properties of phosphorene since the decoration with nickel showed better stability of the sensor and high response towards NO2 at room temperature. The theoretical results explained this behavior by studying the adsorption of oxygen molecules on pristine and nickel loaded phosphorene. The DFT calculations showed that oxygen molecules dissociate on the layer of pristine phosphorene and react with phosphorus atoms (oxidation of the material), while in the presence of the nickel atoms the later play the role of acceptors and interact with the oxygen molecules. Finally, the sensing mechanism towards NO2 was investigated theoretically by studying the charge transfer occurring at the surface of the material during the adsorption process.
I sensori di gas basati sugli ossidi metallici semiconduttori (MOX) si sono rivelati negli ultimi anni una tecnologia estremamente vantaggiosa. Nonostante i progressi fatti in questo campo, questi dispositivi presentano ancora alcuni punti deboliche spingono la ricerca ad effettuare ulteriori indagini per perfezionare il loro funzionamento. I ricercatori hanno cercato di risolvere questi svantaggi in diversi modi, focalizzandosi sullo sviluppo di MOX innovativi, tra cui il drogaggio tramite l’utilizzo di additivi o l’introduzione nel materiale di vacanze di ossigeno a concentrazione controllata. Questa’alternativa sta attirando l’attenzione di molti gruppi di ricerca, anche se, ad oggi, la letteratura scientifica presenta una mancanza di studi su come la disposizione e concentrazione di vacanze di ossigeno influenzano le performance di sensing e solo alcuni lavori preliminari hanno portato a risultati interessanti. Per cercare di ovviare ai limiti dei sensori MOX, una seconda via è stata lo sviluppo e di materiali 2D basati su solfuri metallici, grafene o similari. Il fosforene è uno dei migliori candidati per tale applicazione tecnologica, poiché mostra un'attività elettrica anche a temperatura ambiente, anche se studi preliminari hanno evidenziato un alto tasso di degradazione nel tempo del materiale durante il suo utilizzo. L'obiettivo di questo lavoro è quello di diminuire la temperatura di funzionamento di sensori di gas basati su SnO2 sfruttando il controllo delle vacanze di ossigeno. A tale scopo, è stato fatto inizialmente uno studio della letteratura e un’analisi analitica nell’ambito della DFT per indagare come le vacanze di ossigeno influenzano le proprietà fisico-chimiche del materiale. È stato studiato l'effetto di due diverse concentrazioni di vacanze di ossigeno sulle proprietà chimico-fisiche dello SnO2 bulk. Successivamente è stata studiata la formazione della vacanze in superficie per investigare l'adsorbimento di molecole di ossigeno dall'atmosfera circostante sulla superficie dello SnO2 è stato sintetizzato tramite sintesi sol-gel e la riduzione è stata ottenuta tramite trattamento termico in presenza di H2 a diverse temperature. I risultati hanno mostrato un'alta risposta dei sensori basati su SnO2-x in presenza di basse concentrazioni di NO2 spostando a 130 °C la temperatura ottimale di funzionamento del dispositivo. Questa diminuzione della temperatura operativa implica una diminuzione del consumo energetico del dispositivo Come menzionato precedentemente, il fosforene è uno dei materiali 2D più promettenti per lo sviluppo di sensori di gas chemoresistivi, ma presenta ancora alcuni svantaggi. Molti studi sono stati sviluppati sulla decorazione del fosforene con atomi metallici al fine di migliorare le sue prestazioni per diverse applicazioni tecnologiche, ma non sono stati ancora condotti studi specifici su questa particolare forma di fosforene decorato per applicazioni di sensoristica gassosa. Nello studio qui proposto, sono stati eseguiti calcoli DFT per spiegare come il nichel influenzi le proprietà elettroniche del fosforene, poiché la decorazione con nichel ha mostrato una migliore stabilità del sensore e un’alta sensibilità all’NO2. Tramite simulazione DFT è stato possibile investigare l'adsorbimento delle molecole di ossigeno sul Fosforene tal quale e decorato con nichel. I risultati hanno evidenziato che le molecole di ossigeno si dissociano sullo strato di fosforene tal quale e reagiscono con gli atomi di fosforo, ossidandolo, mentre in presenza dei cluster di nichel è quest’ultimo a svolgere il ruolo di catalizzatore, interagendo con le molecole di ossigeno. Infine, il meccanismo di interazione tra NO2 e la superficie del fosforene tal quale e funzionalizzato è stato caratterizzato teoricamente studiando il trasferimento di carica che avviene sulla superficie del materiale in esame.

Monitoring gases for environmental, industrial and agricultural fields is a demanding task that requires long periods of observation, large quantity of sensors, data management, high temporal and spatial resolution, long term stability, recalibration procedures, computational resources, and energy availability. Wireless Sensor Networks (WSNs) and Unmanned Aerial Vehicles (UAVs) are currently representing the best alternative to monitor large, remote, and difficult access areas, as these technologies have the possibility of carrying specialised gas sensing systems, and offer the possibility of geo-located and time stamp samples. However, these technologies are not fully functional for scientific and commercial applications as their development and availability is limited by a number of factors: the cost of sensors required to cover large areas, their stability over long periods, their power consumption, and the weight of the system to be used on small UAVs. Energy availability is a serious challenge when WSN are deployed in remote areas with difficult access to the grid, while small UAVs are limited by the energy in their reservoir tank or batteries. Another important challenge is the management of data produced by the sensor nodes, requiring large amount of resources to be stored, analysed and displayed after long periods of operation. In response to these challenges, this research proposes the following solutions aiming to improve the availability and development of these technologies for gas sensing monitoring: first, the integration of WSNs and UAVs for environmental gas sensing in order to monitor large volumes at ground and aerial levels with a minimum of sensor nodes for an effective 3D monitoring; second, the use of solar energy as a main power source to allow continuous monitoring; and lastly, the creation of a data management platform to store, analyse and share the information with operators and external users. The principal outcomes of this research are the creation of a gas sensing system suitable for monitoring any kind of gas, which has been installed and tested on CH4 and CO2 in a sensor network (WSN) and on a UAV. The use of the same gas sensing system in a WSN and a UAV reduces significantly the complexity and cost of the application as it allows: a) the standardisation of the signal acquisition and data processing, thereby reducing the required computational resources; b) the standardisation of calibration and operational procedures, reducing systematic errors and complexity; c) the reduction of the weight and energy consumption, leading to an improved power management and weight balance in the case of UAVs; d) the simplification of the sensor node architecture, which is easily replicated in all the nodes. I evaluated two different sensor modules by laboratory, bench, and field tests: a non-dispersive infrared module (NDIR) and a metal-oxide resistive nano-sensor module (MOX nano-sensor). The tests revealed advantages and disadvantages of the two modules when used for static nodes at the ground level and mobile nodes on-board a UAV. Commercial NDIR modules for CO2 have been successfully tested and evaluated in the WSN and on board of the UAV. Their advantage is the precision and stability, but their application is limited to a few gases. The advantages of the MOX nano-sensors are the small size, low weight, low power consumption and their sensitivity to a broad range of gases. However, selectivity is still a concern that needs to be addressed with further studies. An electronic board to interface sensors in a large range of resistivity was successfully designed, created and adapted to operate on ground nodes and on-board UAV. The WSN and UAV created were powered with solar energy in order to facilitate outdoor deployment, data collection and continuous monitoring over large and remote volumes. The gas sensing, solar power, transmission and data management systems of the WSN and UAV were fully evaluated by laboratory, bench and field testing. The methodology created to design, developed, integrate and test these systems was extensively described and experimentally validated. The sampling and transmission capabilities of the WSN and UAV were successfully tested in an emulated mission involving the detection and measurement of CO2 concentrations in a field coming from a contaminant source; the data collected during the mission was transmitted in real time to a central node for data analysis and 3D mapping of the target gas. The major outcome of this research is the accomplishment of the first flight mission, never reported before in the literature, of a solar powered UAV equipped with a CO2 sensing system in conjunction with a network of ground sensor nodes for an effective 3D monitoring of the target gas. A data management platform was created using an external internet server, which manages, stores, and shares the data collected in two web pages, showing statistics and static graph images for internal and external users as requested. The system was bench tested with real data produced by the sensor nodes and the architecture of the platform was widely described and illustrated in order to provide guidance and support on how to replicate the system. In conclusion, the overall results of the project provide guidance on how to create a gas sensing system integrating WSNs and UAVs, how to power the system with solar energy and manage the data produced by the sensor nodes. This system can be used in a wide range of outdoor applications, especially in agriculture, bushfires, mining studies, zoology, and botanical studies opening the way to an ubiquitous low cost environmental monitoring, which may help to decrease our carbon footprint and to improve the health of the planet.

O desenvolvimento de sensores em sistemas para controle ambiental tem-se mostrado uma área de elevado interesse científico e técnico. Os principais desafios nesta área estão relacionados ao desenvolvimento de sensores com capacidade de detecção de várias substâncias. Neste contexto, os capacitores MOS apresentam-se como dispositivos versáteis para a geração de imagens químicas com potencial de detecção e classificação de diferentes substâncias a partir de apenas um único sensor. No presente trabalho, foi proposto um sensor MOS com um perfil geométrico de porta em forma de cata-vento composta por Pd, Au e Pt. A resposta do sensor mostrou ter alta sensibilidade a moléculas ricas em átomos de H, como os gases H2 e NH3. As medidas de capacitância mostraram que o sensor tem uma resposta não linear para H2 e NH3 obedecendo à lei da isoterma de Langmuir. O sensor MOS mostrou-se eficiente na geração de imagens químicas através da técnica de escaneamento por luz pulsada. As imagens químicas correspondentes aos gases H2 e NH3 mostraram diferentes padrões quando o N2 foi utilizado como gás transportador. A diferença entre os padrões aconteceu principalmente devido ao perfil geométrico da porta metálica. A sensibilidade do sensor mostrou dependência com o potencial de polarização. Nas medidas de capacitância, a maior sensibilidade foi observada para potenciais próximos da tensão de banda plana. Já para as imagens químicas, a maior sensibilidade foi observada para potenciais inteiramente na região de depleção. A sensibilidade do sensor também se mostrou dependente do gás transporta- dor. O sensor mostrou ser mais sensível com N2 como gás transportador do que com ar seco. No entanto, o processo de dessorção dos íons H+ resultou ser mais eficiente em ar seco. Os resultados obtidos no presente trabalho sugerem a possibilidade de fabricação de um nariz optoeletrônico utilizando apenas um único sensor MOS.
The development of sensors and systems for environmental control has been shown to be an area of high scientific and technical interest. The main challenges in this area are related to the development of sensors capable of detecting many different substances. In this context, the MOS devices present themselves as versatile devices for chemical imaging with potential for detection and classification of different substances only using one single sensor. In the present work, was proposed a MOS sensor with a wing-vane geometric profile of its gate constituted of Pd, Au and Pt metals. The sensor\'s response showed to have high sensitivity to molecules rich on H atoms, such as H2 and NH3 gases. Capacitance measurements showed that the sensor has a nonlinear response for H2 and NH3 obeying the Langmuir isotherm law. The MOS sensor proved to be efficient in Chemical Imaging generation through the scanned light pulse technique. The chemical images of the H2 and NH3 gases showed different patterns when the N2 was used as carrier gas. The different patterns responses happened mainly due to geometric profile of the metallic gate. The sensor sensitivity showed dependence on the bias potential. In the capacitance measures, greater sensitivity was observed for potential near the flat-band voltage. In the chemical images, the greater sensitivity was observed for bias potential within depletion region. The sensor sensitivity was also dependent on the carrier gas. The sensor showed to be more sensitive with N2 as carrier gas than to dry air. However the desorption process of H+ have been more efficient in dry air. The results obtained in the present work suggest the possibility of manufacturing an optoelectronic nose using only a single MOS sensor.

Dihydro-1,2,4,5-tetrazine-3,6-dicarboxylate was introduced into the chemically stable UiO-66 structure by a postsynthetic linker exchange reaction to create an optical sensor material for the detection of oxidative agents such as nitrous gases. The incorporated tetrazine unit can be reversibly oxidized and reduced, which is accompanied by a drastic colour change from yellow to pink and vice versa. The high stability of the framework during redox reaction was proven by powder X-ray diffraction and nitrogen physisorption measurements.

I dagsläget finns det ingen standardiserad metod för att mäta en enhets tillstånd medhjälp av dofter. Vid tillståndsövervakning av rullningslager är vibrationsmätning denmest dominanta metoden. I samband med vibrationsmätning används i vissa falltemperaturövervakning för att få en bättre insikt på rullningslagrets tillstånd. I det härarbetet undersöks de om en elektronisk näsa kan avgöra ett rullningslagers tillstånd.Innan några mätningar påbörjas monterades en elektronisk näsa ihop i ett hölje sombestår av ett kretskort, metalloxid-sensorer och en fläkt för att styra dofter med ettkonstant flöde mot sensorerna. Den elektroniska näsan styrs av en Arduino Nanomikrokontroller. Utöver e-näsan sättes en enhet ihop tillhörande två temperaturgivareoch en luftfuktighetsgivare som styrs av en Arduino UNO. Enhetens syfte är att kunnakontrollera de rådande förhållandena vid mätningar och för att leta någon form avkorrelation mot e-näsan vid eventuella utslag. Förstörande prover av kullager utfördesför att se om e-näsan reagerar innan ett lagerhaveri. Testerna gjordes i en öppen samtsluten miljö och tre stycken olika oljor används för att smörja lagret. Detta för att seom e-näsan reagerar olika beroende på vilken olja som används. En undersökningutförs ifall den elektroniska näsan kan separera på de tre oljorna som används ilagertesterna. För att utvärdera mätresultaten används Excel och Minitab, därprincipalkomponentanalyser genomförs på all mätdata. Efter att alla lagerprover harverkställts utfördes en uppföljning av rullningslagrena för att studera deras tillstånd,detta genom ett optiskt mikroskop.Det framgår i rapporten att med hjälp av analysmetoden PCA syns det att denelektroniska näsan kunde skilja på hydraulolja, motorolja och växellådsolja. Utslag iPCA för de olika mätserierna blev inte identiska men det blev tydligaklusterindelningar hos samtliga mätserier. Genomförd studie visade att med delagerhaveri samt temperaturer går det inte att avgöra ett kullagers tillstånd med hjälpav en elektronisk näsa. Eftersom att de specifika gas-sensorerna som användes till enäsaninte gav någon form av utslag vid mätningarna. Den elektroniska näsanreagerade däremot vid totalhaveri av kullager, vilket är för sent i ett förebyggandeunderhållsperspektiv. Detta medförde att den elektroniska näsan inte kan användas förtillståndsövervakning av det specifika kullagret som användes vid denna studie.
At present, there is no standardized method of measuring a device's condition with thehelp of odors. In condition monitoring of rolling bearings, vibration measurement isthe most dominant method. In case of vibration measurement, temperature monitoringis used in some cases to get a better insight into the condition of the bearing. In thiswork, it is investigated whether an electronic nose can determine the condition of arolling bearing.Before any measurements began, an electronic nose is assembled in a housingconsisting of a circuit board, metal oxide sensors and a fan for stearing odors with aconstant flow towards the sensors. The electronic nose is controlled by an ArduinoNano which is a microcontroller. In addition to the e-nose, a unit is connected to twotemperature sensors and a humidity sensor controlled by an Arduino UNO. The unit'spurpose is to monitor the status and to look for any kind of correlation with the e-nosein case of any possible findings. Destructive specimens of ball bearings are performedto see if the e-nose responds prior to a bearing failure. Tests are conducted in an openand closed environment and three different oils are used to lubricate the bearings.This to see if the e-nose acts differently depending on the oil that is used. Aninvestigation is conducted if the electronic nose can separate the three different typesof oils that is used in the destructive bearing tests. To evaluate the measurementresults, Excel and Minitab are used, where principal component analysis is performedon all measurement data. After all bearing tests have been performed, a follow-up ofthe rolling bearings condition is performed, this through an optical microscope.The report shows that using the PCA analysis method, it appears that the electronicnose could distinguish between hydraulic oil, engine oil and gear oil. In the PCA forthe different measurement series the results did not become identical, but clusterdivisions became clear in all measurement series. Completed study showed that withthese bearing failures and temperatures, it is not possible to determine the condition ofthis ball bearer using an electronic nose. Because the specific gas sensors used for thee-nose did not give any kind of impact during the measurements. On the other hand,the electronic nose responded to a total failure of a ball bearing, which is too late in apreventative maintenance perspective. Therefore, the electronic nose cannot be usedfor condition monitoring of the specific ball bearing used in this study.

La mesure sur site et en temps réel des concentrations de gaz est cruciale pour la compréhension et la surveillance des processus industriels et environnementaux. Ces dernières années, il devient de plus en plus nécessaire de développer des outils d'analyse multigaz portatifs permettant la détection in situ de mélanges gazeux complexes, principalement pour des raisons de sécurité, de processus et d'environnement. Une approche prometteuse est basée sur l'intégration de différentes parties de systèmes analytiques de détection (par exemple pré-concentrateur, colonne de chromatographie en phase gazeuse ou encore capteurs gravimétriques) dans une puce en silicium en utilisant les technologies standards de microélectronique. Toutefois, chacun de ces dispositifs doit être fonctionnalisé avec une couche sensible appropriée. Les Metal-Organic-Framework (MOF), des matériaux hybrides cristallins microporeux aux propriétés modulables, sont intéressant pour ce type d'application en raison de leur surface spécifique élevée et de leur stabilité chimique. Cependant, ces matériaux sont généralement synthétisés par des procédés en solution (synthèse solvothermale), ce qui complique la croissance de couches minces continues et leur intégration dans des micro-dispositifs. Ce travail a pour objectif le développement d’un procédé de synthèse en phase vapeur pour produire des films minces de Zeolitic Imidazolate Framework 8 (ZIF-8), un MOF particulièrement intéressant. La méthode de croissance est basée sur le dépôt de couches de ZnO par Atomic Layer Deposition (ALD) sur un substrat, suivi de sa conversion et de la formation de ZIF-8 par exposition cyclique à la vapeur d'eau et au ligand organique en phase vapeur. Cette approche a permis la formation de films minces d'épaisseur comprise entre 5 et 200 nm, indépendamment de l'épaisseur de ZnO initiale. L'impact des paramètres du procédé (température du substrat, pression de vapeur d'eau...) sur la croissance du MOF a été étudié. La composition, la morphologie et la cristallinité ont été examinées à l'aide d'un large panel de techniques de caractérisation (AFM, DRX, MEB, FTIR). De plus, les mécanismes de croissance ont été étudiés par XPS et ToF-SIMS pour comprendre le rôle de l'eau pendant la réaction et plusieurs hypothèses ont été émises. Enfin, les films ont été activés thermiquement et la porosité a été évaluée par ellipsométrie-porosimétrie. Le volume des pores représente 30 % du volume des films dans certains cas. Les propriétés d'adsorption des films ont également été étudiées à l'aide de capteurs de gaz gravimétriques. En effet, des films de ZIF-8 ont été déposés sur des microbalances à cristal de quartz (QCM) pour étudier les interactions entre la couche et plusieurs gaz (méthanol, acétone et eau) afin de déterminer l'intérêt des films minces de ZIF-8 dans des capteurs de ce type. Ce travail montre que les capteurs fonctionnalisés avec du ZIF-8 permettent la détection de tous les gaz indépendamment dans les gammes de concentration testées. Cependant, la sensibilité de la détection du méthanol est fortement impactée par l'ajout d'humidité relative
On-site and real-time measurement of gas concentrations are crucial for both the understanding and the monitoring of industrial and environmental processes. In recent years, there is an increasing need to develop portable multi-gas analysis tools allowing in situ detection of complex gas mixtures mainly due to safety, process and environmental considerations. A promising approach is based on the integration of the different parts of the analytical system (i.e. pre-concentrator, gas chromatography column, gravimetric sensors) in a silicon die by using standard microelectronic technologies. Each of these devices need to be coated by an appropriate functional layer. Metal Organic Frameworks (MOF), hybrid microporous crystalline materials with tuneable properties, are attractive for this type of application regarding their high specific surface area and chemical stability. However, these materials are usually synthetized via solvothermal techniques, which complicates the growth of continuous thin films and their integration in micro-devices. This work focuses on the development of a vapor phase-based route to produce Zeolitic Imidazolate Framework 8 (ZIF-8) thin films, a MOF of particular interest. The growth method is based on the deposition of ZnO layers by atomic layer deposition (ALD) on a substrate followed by ZIF-8 formation using cyclic exposure to water vapour and organic ligand in the gas phase. This approach allowed formation of thin films with tunable thickness between 5 and 200 nm, independently of the initial ZnO thickness. The impact of the process parameters (temperature of the substrate, water vapor pressure…) on the MOF growth was studied. The composition, morphology and crystallinity were examined using a wide range of characterization techniques (AFM, SEM, XRD and FTIR). Moreover, the growth mechanism was investigated by XPS and ToF-SIMS to understand the role of water during the reaction and several hypotheses were given. Finally, the as-synthesized films were thermally activated and the porosity was assessed using ellipsometric-porosimetry. Pore volume represents 30 % of the volume of the films in some cases. The adsorption properties of the films were also investigated using gravimetric gas sensors. Indeed, ZIF-8 films were grown on quartz crystal microbalance to study the interactions between the layer and several gases (methanol, acetone and water) in order to determine the benefit of ZIF-8 thin films in sensors. This work shows that the sensors coated with the ZIF-8 enable the detection of all the gases independently in the range of concentration tested. However, the sensitivity of the methanol detection is highly impacted by the addition of relative humidity

Depuis quelques années, les explosifs artisanaux à base de peroxyde sont fréquemment utilisés dans les actes de terrorisme. Leur simplicité de conception ne les rend pas moins inoffensifs car ils sont tout aussi puissants que ceux à base de TNT (trinitrotoluène). Au regard des enjeux majeurs de la sécurité globale et en particulier de la protection du citoyen, il devient nécessaire de bénéficier d'instruments de détection fiables. C'est dans ce cadre que s'inscrit ce travail de thèse qui vise à développer un capteur intégré, sensible et sélectif aux traces d'explosifs, notamment ceux à base de peroxyde. Ce nez électronique est constitué d'une matrice de transistors à nanotubes de carbone (CNTFET) et d'une électronique et traitement des données. Après une brève introduction relative aux CNTFET pour la détection gazeuse, nous présentons les bases de l'élaboration d'une modélisation électrique du capteur. Cette modélisation a pour but, à terme, de permettre aux concepteurs decircuits intégrés de bénéficier d'un support de simulation des CNTFET, nécessaire à la mise en oeuvre de l'électronique de contrôle et de conditionnement des signaux. Nous détaillerons également ce qui constitue selon nous l'étape fondamentale précédant l'élaboration d'un modèle compact prédictif basé sur la physique, c'est à dire la compréhension topologique du réseau de nanotubes. Nous détaillerons alors différentes probabilités de contacts entre nanotubes. Nous présentons ensuite,l'élaboration de l'électronique permettant le contrôle des potentiels appliqués aux CNTFET et le conditionnement des signaux électriques. Ce conditionnement a pour objectif d'acheminer les réponses électriques du capteur vers des architectures de traitement de données utilisées pour la détection des différents gaz cibles. L'électronique intégrée en technologie CMOS HV (haute tension) est alimentée par pile basse tension. Des pompes de charge, élévateurs de tension, générant ces hautes tensions ont été étudiées, modélisées et réalisées. Nous proposons également dans ce manuscrit une nouvelle architecture de pompe de charge qui constitue, dans certaines plages d'utilisation, une alternative intéressante aux pompes de charge les plus performantes utilisées jusqu'à présent
For the last few years, improvised peroxide based explosives are frequently used in acts of terrorism. Their simple design does not make them less threatening than those based on TNT because they are equally as powerful as those based on TNT (trinitrotoluene). In view of the major issues of the overall safety and, in particular, the citizens' protection, it becomes necessary to enjoy reliable detection instruments. Such is the background of this PhD work which aims to develop a built-in sensor,sensitive and selective to traces of explosives, especially those based on peroxide. This electronic nose is made up of a network of carbon nanotube field-effect transistors (CNTFET), and data processing hardware. After a brief introduction relating to CNTFETs for gaseous detection, we will provide the basis for the elaboration of an electronic modeling of the sensor. This modeling aims, at the end, to allow designers of integrated circuits to benefit from a simulation support of CNTFETs, required to the implementation of control and signal conditioning electronics. We will also detail what are the fundamental steps mandatory before the development of a predictive compact model based on physics, which means the topological understanding of the nanotubes network. Then, we will describe different probabilities of contacts between nanotubes. Later, we will introduce the elaboration of the electronics allowing the control of the voltages applied to the CNTFETs and the electrical signals conditioning. The objective of this conditioning is to carry electrical responses from the sensor to data processing architectures used for the detection of the different target gasses. High Voltage CMOS integrated electronics are powered by low-voltage batteries. Charge pumps and voltage boosters which generate these high voltages, have been investigated, modeled and carried out. We also provide in this dissertation a new charge pump architecture which offers, in some ranges of application, an interesting alternative to the most efficient charge pumps used until now

碩士
國立高雄應用科技大學
化學工程與材料工程系博碩士班
106
In this study, inkjet printing technology was used to prepare a looped electrode composed of silver nanoparticles on a flexible polyimide (PI) film, and a porous semiconductor-type gas-sensing material such as zinc oxide and copper oxide, which were derived from a metal-organic framework material was used as sensing layer, and coated onto nanosilver loop type electrode. To investigate the sensing capability of the homemade gas sensor under reducing gas atmosphere at room temperature with a low wattage UV-LED (10 W) lamp irradiated, to improve the semiconductor gas sensitive materials need to be applied to the limitations of high-temperature environment. Using ethylene glycol as a reducing agent and polyvinylpyrrolidone (PPV) as a protective agent, silver nitrate (AgNO3) was reduced by a simple polyol reduction method to prepare nanosilver particles. X-ray diffraction (XRD) results indicate that the silver nanoparticles are spherical metal silver with face-centered cubic structure. The particle size is approximately 60-80 nm by Scanning Electron Microscope (SEM) and Transmission Electron Microscopy (TEM) and particle size analyzer. The silver nanoparticle was formulated into 5 wt% silver ink, and the ink was filled in a commercially available EPSON T50 printer ink cartridge. The nanosilver loop type electrode is printed on the polyimide film and then coated with a layer of gas sensitive material, wherein the sensing layer is ZnO (N-type) and CuO (P-type), and the formation of heterogeneous interface (P-N Junction) of ZnO mixed with CuO (ZnO/CuO) to complete the preparation of sensors. The sensors are placed in a homemade gas sensing chamber, and the sensing test is carried out under reducing gas atmosphere (0-400 ppm) at room temperature with a low wattage UV-LED (10 W) lamp irradiated. The sensors was connected to a universal meter (Keithley 2400), and the current value was read at different reducing gas concentrations. After the computer software was recorded, the sensing performance of the gas sensor at room temperature was investigated. When the sensor was used to sense 50 ppm acetone at room temperature, the response values of ZnO, CuO, and ZnO/CuO were 34.9, 20.9 and 63.6 respectively. The response time (Tres) was 3, 52 and 5 seconds respectively, the recovery time (Trec) was 5, 14 and 8 seconds, respectively, and the sensed instantaneous current value significantly changed with increasing acetone gas concentration, and was an effective acetone gas sensor. It is worth noting that sensors with heterostructure materials (ZnO/CuO) have obviously synergistic effects. Which show that the sensors can effectively improve the limitations of conventional metal oxide semiconductor gas sensors operating at high operating temperature, and have good sensing ability for the acetone gas with low ppm concentration at room temperature.

碩士
國立成功大學
微電子工程研究所
105
In this thesis, a series of GaN/AlGaN Schottky diode based hydrogen sensors have been fabricated and studied. Pd was chosen as Schottky contacts metal to detect hydrogen gas. Hydrogen sensing behaviors of the studied devices are investigated by sensing response and response time under different gas concentrations, and we compare the gas sensing properties of devices with and without H2O2 treatment. First, Pd/HfO2/GaN/AlGaN Schottky diode-type hydrogen sensor is fabricated and studied. Using RF sputtering to deposite HfO2 between Pd and GaN. HfO2 layer can decrease steady current in air to improve gas sensing capability. So, based on GaN and high quility insulator gas sensor to provide important potential. The thermionic emission (TE) equaiton is employed to characterize the current voltage behaviors of studied M-O-S device upon introduction of hydrogen gases. The schottky barrier height extracted from the TE equation is observe to be sensitive to hydrogen gases under various concentrations. Hydrogen sensing behavoirs of the studied M-O-S device are investigated in terms of those diode paraments, sensing responses, and response times. Second, Using hydrogen peroxide to conduct oxidation reaction on the GaN/AlGaN surface. Based on the strong oxidation property, a thin GaOx layer could be formed by an appropriate immersion of H2O2 solution. The formed GaOx layer increases the Schottky barrier height, effective adsorption sites and remarkably improves the related hydrogen gas sensing capability. Third, a chemically electroless plated (EP)-Pd/GaOx/GaN/AlGaN Schottky diode-type hydrogen sensor is fabricated and studied. Using this method can improve fermi level pinning and increase surface rougheness. Therefore, the EP-based Schottky diode have excellent rectification ratio and lower reverse saturation current. Otherwise, based on EP Pd films have higher surface rougheness through AFM, and its can be beneficial to detection hydrogen. The thermionic emission (TE) equaiton is employed to characterize the current voltage behaviors of studied EP device upon introduction of hydrogen gases. The schottky barrier height extracted from the TE equation is observe to be sensitive to hydrogen gases under various concentrations. Hydrogen sensing behavoirs of the studied EP device are investigated in terms of those diode paraments, sensing responses, response times, activation enegy.

The metal-organic framework (MOF) compounds have witnessed rapid growth in the past decade and currently emerged as a highly unique area in the field of chemistry, materials science, and multiple branches of engineering. It presents applications in diverse fields such as gas sorption, catalysis, ionic conductivity, sensing etc. These compounds are built by the inorganic metal ions which are bridged by organic linkers to form extended structures. These compounds are mainly synthesized by either one-pot synthesis or in a sequential manner. In the former case, the inorganic metal ions and the respective organic linker are reacted together in a particular solvent or solvent mixture, whereas in the later case, a metalloligand is prepared by using the organic linker and the primary metal ion, which react with the secondary metal ion forming the desired structure. In this thesis, the synthesis of metal-organic framework compounds by one-pot synthesis as well as the sequential synthesis is presented. The structures of all the synthesized compounds have been determined by single crystal X-ray diffraction technique. The prepared compounds were employed in the study of sensing of nitroaromatic compounds, toxic metal ions and highly oxidizing anions. In addition, detailed studies of heterogeneous catalysis employing the prepared MOFs were investigated along with catalysis by metal nanoparticle incorporated within MOFs. In select cases, the labile nature of the lattice water molecules was established by performing in-situ single crystal to single crystal (SCSC) structural transformation studies. In addition, the proton conductivity and the magnetic behavior have also been studied. Chapter 1 of the thesis presents a brief overview on metal-organic framework compounds and summarizes its various important properties. In chapter 2, the synthesis, structure, and characterization of heterometallic metal-organic framework compounds using 2-mercaptonicotinic (H2mna) and Cu(I) / Ag(I) based two metalloligands, [Cu6(Hmna)6] and [Ag6(Hmna)2(mna)4](NH4)4 are presented. In chapter 3, we present the synthesis, structure and nitroaromatic sensing behavior of [Ag6(mna)6](NH4)6 metalloligand based heterometallic metal-organic framework compounds. In chapter 4, the synthesis, structure and Lewis acid catalytic behavior of 6-mercaptonicotinic acid based heterometallic metal-organic framework compounds are presented. In chapter 5, the stabilization of the palladium nanoparticles in the newly synthesized 1,10-phenanthroline based metal-organic framework compounds and their catalytic behavior is presented. In chapter 6, we present the synthesis, structure and the sensing behavior of hazardous chemicals such as toxic metal ions and highly oxidizing anions. In addition, the adsorption and desorption of synthetic dye molecules by the metal-organic framework compounds are also presented.