In this master´s thesis various types of gas sensors, their characteristics, principle, active layer and structure are described. This work is focused on semiconductor gas sensors. In the experimental part gas test station is used to measure the main characteristic of commercial sensor Figaro TGS 822 and own SnO2 gas sensors and reaction to oxygen. Both sensors and measurement results are compared with each other.

This diploma thesis discusses the gas sensor preparation via anodic oxidation. It names sensor types, deals with the sensing principle of electrochemical sensors in detail and submits sensor parameters. It describes preparation technology and characterization technology methods. In the experimental part, it focuses on both the measurement methodology and the electrochemical oxygen sensor covered with titanium dioxide nanocolumns fabrication. Not the least it discusses acquired research results.

The aim of the diploma thesis was to prepare and characterize fluorescence sensor systems based on fluorophores and supramolecular components - cyclodextrins - attached to solid supports. In this work, functionalized 75 µm glass beads and two types of Nafion membranes were used as negatively charged solid surfaces. Derivatives of naphthalimide with a positively charged part allowing the attachment to surfaces were synthesized. The positively charged naphthalimide derivative was then attached on negatively charged surfaces via electrostatic interactions and the binding to the solid supports was examined using UV-VIS spectroscopy. Alternatively, the positively charged β-cyclodextrin derivative was also attached to the surface in an equimolar ratio with PNI-HEMPDA. The focus of the work were measurements of fluorescence sensor responses in the gas and liquid phase to linear alcohols - methanol to n-hexanol - for all sensor systems. For the studied sensor systems, the selected sensor parameters were determined - sensitivity, the limit of detection, linear dynamic range and a sensor response time constant. A practical application of the novel sensor system for the detection of ethanol in gasoline was examined. Fluorescence sensor response measurements of the prepared systems based on naphthalimide and...

The precise determination of the type and concentration of gases is of increasing importance in numerous applications. Despite the diverse operating principles of today´s gas sensors, technological trends can be summarized with the keyword miniaturization, because of the resulting benefits such as integrability and energy efficiency. This work deals with the development and fabrication of novel nanowire based gas sensors, which in comparison to conventional devices have an advantageous combination of high sensitivity and selectivity with low power consumption and small size. On the basis of grown silicon nanowires, sensors based on the functional principle of classical Schottky barrier field effect transistors with abrupt metal-semiconductor contacts are fabricated. The sensing performance of the devices is investigated with respect to the detection of ammonia. Ammonia concentrations down to 170 ppb are measured with a sensor response of more than 160 % and a theoretical limit of detection of 20 ppb is determined. Selectivity investigations show that no cross sensitivity to most common solvents occurring in living spaces exists. Moisture influences on the device are studied and reveal that the sensor responds within seconds, making it potentially suitable as humidity sensor. Moreover, it is shown that a higher relative humidity and higher temperatures decrease the sensor sensitivity. In terms of possible applications, it is a great advantage that the maximum sensitivity is achieved at 25 °C. With respect to sensitivity and selectivity an enhancement is demonstrated compared to most nanosensors known from the literature. Hence, the technology offers the potential to complement conventional measurement systems in future sensor technology especially in portable applications. / Die präzise Bestimmung der Art und Konzentration von Gasen erlangt in zahlreichen Anwendungsgebieten zunehmend an Bedeutung. Trotz der vielfältigen Wirkprinzipien heutiger Gassensoren lassen sich die technologischen Trends mit dem Schlagwort Miniaturisierung zusammenfassen, da sich daraus entscheidende Vorteile wie Integrierbarkeit und Energieeffizienz ergeben. Diese Arbeit beschäftigt sich mit der Entwicklung und Herstellung neuartiger nanodrahtbasierter Gassensoren, welche im Vergleich zu klassischen Sensoren eine vorteilhafte Kombination von hoher Sensitivität und Selektivität bei geringem Stromverbrauch und geringer Größe aufweisen. Auf der Grundlage gewachsener Silizium-Nanodrähte werden Sensoren mit abrupten Metall-Halbleiter-Kontakten hergestellt, welche auf dem Funktionsprinzip klassischer Schottkybarrieren-Feldeffekttransistoren beruhen. Die Eignung der Sensoren wird in Bezug auf die Detektion von Ammoniak untersucht. Dabei kann eine minimale Ammoniakkonzentration von 170 ppb mit einer Signaländerung von mehr als 160 % gemessen werden, wobei die theoretische Nachweisgrenze mit 20 ppb ermittelt wird. Selektivitätsuntersuchungen zeigen, dass keine Querempfindlichkeit gegenüber den am häufigsten in Wohnräumen vorkommenden Lösungsmitteln besteht. Feuchtigkeitseinflüsse auf den Sensor werden untersucht und es wird nachgewiesen, dass der Sensor Ansprechzeiten im Sekundenbereich besitzt, was ihn zu einem potenziell geeigneten Feuchtigkeitssensor macht. Darüber hinaus wird gezeigt, dass eine höhere relative Luftfeuchtigkeit und höhere Umgebungstemperaturen die Sensorsensitivität verringern. In Bezug auf mögliche Einsatzgebiete stellt die maximale Empfindlichkeit bei 25 °C einen großen Vorteil da. Bezogen auf Sensitivität und Selektivität wird somit eine Verbesserung im Vergleich zu den meisten aus der Literatur bekannten Nanosensoren demonstriert. Damit bietet die Technologie das Potential, konventionelle Messsysteme in zukünftiger Sensorik vor allem in portablen Anwendungen zu ergänzen.

Greenhouse gas emissions in indoor or outdoor areas are dangerous and can have short- or long-term effects on people’s health. There are several methods to monitor the air quality in such environments. This thesis project attempts to design and evaluate a wireless sensor network with two main characteristics such as long range and low power consumption. The sensor network is built upon Long Range Wide Area Network (LoRaWAN) protocol and is composed of sensor nodes and gateways. The sensor nodes are built upon a Raspberry Pi model 3B, a LoRa SX1276 transceiver and gas sensors. The sensors are intended to measure CO2, CH4, temperature, pressure and relative humidity. The collected data is then logged and sent to The Things Network (TTN) via a backhaul connection.

L’utilisation de micromembranes suspendues chauffées par effet Joule comme source de rayonnement infrarouge est une piste prometteuse pour la réalisation de détecteurs de gaz compacts, basse consommation et à bas coût. Afin d’améliorer l’efficacité de ces dispositifs récemment introduits, il est nécessaire d’optimiser ceux-ci à la fois du point de vue optique et thermique.En ajoutant des résonateurs plasmoniques frustrés sur les membranes, il est possible de modifier l’émissivité de ces dernières, afin de contrôler spectralement et angulairement le rayonnement émis. De cette façon, la puissance utile est augmentée, tandis que la consommation électrique diminue. D’autre part, l’étude en profondeur des rôles des différents canaux thermiques conduit à relier rayon de la membrane, temps de chauffe et énergie disponible par mesure et de définir un régime optimal de fonctionnement dynamique.Finalement les membranes sont fabriquées en salle blanche et caractérisées électriquement, optiquement et mécaniquement afin d’estimer les gains en performances. La réalisation d’un prototype de capteur de CO2 à 4,26 µm à partir de ces sources indique des précisions de l’ordre de la vingtaine de ppm pour une consommation d’un milliwatt, en compétition favorable avec l’état de l’art mondial dans ce domaine. / Joule-heated suspended microhotplates can be used as infrared sources in cheap, low-consumption spectroscopic gas sensors. To enhance the very low efficiency of first generation structures, both their thermal and optical designs have to be optimized.The implementation of frustrated plasmonic resonators on top of the membrane grants both spectral and angular control of its emissivity. It is thus possible to make it radiate only at the frequencies absorbed by the gas under study, and in the solid angle of the detector. This leads to an increase in useful radiated power while the overall electrical consumption is decreased. Dynamical studies of membrane heating provide welcome insight on the relationship between membrane radius, heating time and energy consumption per measurement. The existence of a compromise is demonstrated in order to maximize the radiative efficiency, and its physical interpretation is detailed.Eventually, membranes fabricated in LETI’s clean room were characterized to measure their electrical, optical and mechanical properties. The implementation of such sources in a CO2 prototype sensor led to state-of-the-art results, with a few dozen ppm sensitivity with a power consumption of only one milliwatt.

Mobile devices for the personalized detection of health and environmental hazards are becoming the basis for futuristic sensing technologies. In recent decades, air and environmental pollution levels have risen globally. Therefore, environmental protection must be strengthened by developing sensors that detect pollutants. The monitoring of these pollutants with high spatial coverage requires inexpensive electronic gas sensors and self sustainable sensing systems that can be deployed everywhere. This dissertation reports on technological developments to provide solutions for inexpensive, compact, power efficient, and easily deployable toxic gas sensors and integrated systems using semiconducting metal-oxide thin-film transistors (TFTs). The first part of the dissertation introduces the fabrication and characterization of an amorphous indium gallium zinc oxide (IGZO) TFT as a toxic gas sensor. In contrast to existing metal-oxide gas sensors, which are active either with light activation or at high temperature, the developed IGZO TFT sensors are operable at room temperature and require only visible light activation to revive them after exposure to NO2. IGZO TFT sensors exhibited remarkable selectivity and sensitivity to low concentrations of nitrogen dioxide (NO2). The second part of the dissertation introduces the design and realization of the IGZO-based fully integrated gas detectors. Unlike existing gas-sensing systems, which have discrete hardware for signal conditioning, read-out, and data acquisition, the developed integrated detectors constitute thesemodules integrated using IGZO TFT technology. The integrated detectors detect ambient NO2 gas and generate a digital output that is proportional to the ambient gas concentrations. Two types of integrated gas detectors were developed that differ in their mode of operation and circuitry design. These detectors are scalable and pave the way for portable systems to realize various gas-sensing applications, including smart cities and sustainable ecosystems. The success of personalized monitoring devices relies on the following factors: minimum power consumption, selectivity, and stability under extreme conditions that determine overall performance. One of the best solutions to minimize power consumption in these devices is to have a complementary energy-harvesting feature. Hence, the dissertation concludes with the design of self-powered sensors, which are IGZO sensors with self-powering capabilities. Self-powered sensors are p-n heterojunction sensors, developed using IGZO and hybrid-perovskites.

京都大学 / 0048 / 新制・論文博士 / 博士(農学) / 乙第12762号 / 論農博第2785号 / 新制||農||1016(附属図書館) / 学位論文||H25||N4785(農学部図書室) / 30614 / (主査)教授 奥村 正悟, 教授 中野 隆人, 教授 吉村 剛 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

A systematic investigation has been performed for "Electric Nose", a system that can identify gas samples and detect their concentrations by combining sensor array and data processing technologies. Non-silicon based microfabricatition has been developed for micro-electro-mechanical-system (MEMS) based gas sensors. Novel sensors have been designed, fabricated and tested. Nanocrystalline semiconductor metal oxide (SMO) materials include SnO2, WO3 and In2O3 have been studied for gas sensing applications. Different doping material such as copper, silver, platinum and indium are studied in order to achieve better selectivity for different targeting toxic gases including hydrogen, carbon monoxide, hydrogen sulfide etc. Fundamental issues like sensitivity, selectivity, stability, temperature influence, humidity influence, thermal characterization, drifting problem etc. of SMO gas sensors have been intensively investigated. A novel approach to improve temperature stability of SMO (including tin oxide) gas sensors by applying a temperature feedback control circuit has been developed. The feedback temperature controller that is compatible with MEMS sensor fabrication has been invented and applied to gas sensor array system. Significant improvement of stability has been achieved compared to SMO gas sensors without temperature compensation under the same ambient conditions. Single walled carbon nanotube (SWNT) has been studied to improve SnO2 gas sensing property in terms of sensitivity, response time and recovery time. Three times of better sensitivity has been achieved experimentally. The feasibility of using TSK Fuzzy neural network algorithm for Electric Nose has been exploited during the research. A training process of using TSK Fuzzy neural network with input/output pairs from individual gas sensor cell has been developed. This will make electric nose smart enough to measure gas concentrations in a gas mixture. The model has been proven valid by gas experimental results conducted.

An optical fiber has been developed that can be used as a chemical gas sensor. Fabrication of the optical fiber produces a fiber that has a solid core with a porous cladding. The porous cladding region is made from a spinodally phase separable glass where the secondary phase is removed through dilute acid leaching. A non-phase separable glass composition is used for the core region. The properties of the phase separable glass are dependent on the processing conditions and the thermal history of the glass after the porosity has been achieved. Investigation of how processing conditions affected the pore structure was conducted to determine what pore characteristics are achievable for the glass composition used. Phase separation temperature, removal of silica gel deposited in the pores, and the post fabrication heat treating were used as experimental processing conditions. A maximum useable average pore size of approximately 29 nm was achieved. Maximum pore volume in the experimental groups was 0.4399 cc/g. Most heat treatments of the porous glass caused consolidation of the pore structure, with some conditions producing pore coarsening. / Master of Science