Volatile organic compounds (VOCs) in the indoor air have adverse effects on the dwellers residing in a building or a vehicle. One of these effects is called sick building syndrome (SBS). SBS refers to situations in which the users of a building develop acute health effects and discomfort depending on the time they spend inside some buildings without having any specific illness. Furthermore, monitoring volatile organic compounds could lead to early diagnosis of specific illnesses through breath analysis. Among those VOCs formaldehyde, acetaldehyde can be listed. In this thesis, VOC detecting thin film sensors have been investigated. Such sensors have been manufactured using semiconducting metal oxides, ligand activated gold nanoparticles and Graphene/TiO2 mixtures. Advanced gas deposition unit, have been used to produce NiO thin films and Au nanoparticles. DC magnetron sputtering has been used to produce InSnO and VO2 thin film sensors. Graphene/TiO2 sensors have been manufactured using doctor-blading. While presenting the results, first, material characterization details are presented for each sensor, then, gas sensing results are presented. Morphologies, crystalline structures and chemical properties have been analyzed using scanning electron microscopy, X-ray diffraction and X-ray photo electron spectroscopy. Furthermore, more detailed analyses have been performed on NiO samples using extended X-ray absorption fine structure method and N2 adsorption measurements. Gas sensing measurements were focused on monitoring formaldehyde and acetaldehyde. However, responses ethanol and methane were measured in some cases to monitor selectivity. Graphene/TiO2 samples were used to monitor NO2 and NH3. For NiO thin film sensors and Au nano particles, fluctuation enhanced gas sensing is also presented in addition to conductometric measurements.

O presente trabalho envolveu a eletrossíntese de três polímeros da família dos poli(p-fenilenovinileno)s, PPVs, apresentando como substituintes grupos alcóxi de cadeia longa. Esses polímeros foram caracterizados espectroscopicamente (RMN de 1H, IV e UV/VIS), termicamente (TG), por cromatografia por exclusão de tamanho (SEC), eletronicamente por voltametria cíclica e eletricamente por meio de curvas I x V em dispositivos do tipo sanduíche (metal/polímero/metal). Os polímeros foram utilizados na construção de sensores de gases para avaliação da capacidade sensitiva a vapores orgânicos, mostrando-se promissores para utilização em narizes eletrônicos. Construíram-se, também, dispositivos emissores de luz orgânicos (OLEDs) com utilização desses polímeros como camada ativa, no intuito de se conhecer sua aplicabilidade em dispositivos optoeletrônicos. Para tal, foram feitas determinações de luminância e de eficiência quântica de luminância dos OLEDs construídos. Os dispositivos do tipo sanduíche, os OLEDs e as medidas correspondentes foram realizados em Curitiba, em colaboração com o Prof. Dr. Ivo Alexandre Hümmelgen, líder do Grupo de Dispositivos Optoeletrônicos Orgânicos do Departamento de Física da Universidade Federal do Paraná. / The present work describes the electrosynthesis of three polymers of the poly(p-phenylenevinylene) (PPV) family, having at least one long chain alkoxy group as substituent. These polymers were characterized by spectroscopic analyses (1H NMR, IR and UV-Vis), thermogravimetry (TG), size exclusion chromatography (SEC), cyclic voltammetry and electrically by current vs. potential plots obtained from metal/polymer/metal sandwich devices. The polymers were tested as active layers in gas sensors for organic vapour analyses aimed for future use in electronic noses. The same polymers were also employed in organic light emitting diodes (OLEDs) in which the luminance and the luminance quantum efficiency were measured. Both the sandwich devices and the OLEDs were made in Curitiba with the collaboration of Prof. Ivo Hümmelgen, head of the Group of Organic Optoelectronic Devices at the Physics Department of the Federal University of Paraná (UFPR).

The general aim of Master’s thesis is to design and execute electronics in the SMT device view for thin film gas sensors and to study principle of gas sensor functionality based on semiconducting oxides. The SMT device contains temperature controller and electronics which is able to scan the concentration of gas on the sensor surface. It is designed for controlling of four sensors and has to communicate with computer for setting of initial conditions and scanning of concentration of gas. The practical part of Master’s thesis contains design and construction of electronics and software making.

O2,Pt|YSZ-Elektroden aus Platin und Yttriumoxid-stabilisiertem Zirkoniumdioxid (YSZ) gehören zu den am häufigsten verwendeten Festelektrolyt-Elektroden. Ein wichtiges Einsatzgebiet ist die Bestimmung des Restsauerstoffgehaltes in Autoabgasen mittels sogenannter Lambdasonden. Für die Messfähigkeit des Sensors ist ein möglichst geringer Transportwiderstand aller beteiligten Spezies in der jeweiligen Phase der Elektrodenstruktur vorteilhaft, sowie ein geringer Durchtrittswiderstand der Elektrodenreak-tion. Neben der Messfähigkeit des Sensors ist auch dessen Alterungsbeständigkeit wichtig. In dieser Arbeit wurden anwendungsnahe O2,Pt|YSZ-Cermet-Elektroden im Modellsystem sowie neue und realistisch gealterte Lambdasonden untersucht. Für die Charakterisierung der Modellelektroden wurden sowohl übliche Methoden (Impedanzspektroskopie, Festelektrolyt-Cyclovoltammetrie und Chronoamperometrie) eingesetzt, als auch bisher für Festelektrolyt-Elektroden nicht verbreitete Metho-den wie cyclovoltammetrische Untersuchungen in wässrigen Elektrolyten. Erstmalig wurden im tatsäch-lichen Betrieb über die gesamte Lebensdauer eines Automobils gealterte Lambdasonden mit diesen Methoden untersucht. Dies eröffnet neue Charakterisierungsmöglichkeiten zur Anwendung in der Ent-wicklung neuer und der Diagnose gealterter Elektroden von Lambdasonden.

Energy efficiency is a key requirement for wireless sensor nodes, biomedical implants, and wearable devices. The energy consumption of the sensor node needs to be minimized to avoid battery replacement, or even better, to enable the device to survive on energy harvested from the ambient. Capacitive sensors do not consume static power; thus, they are attractive from an energy efficiency perspective. In addition, they can be employed in a wide range of sensing applications. However, the sensor readout circuit–i.e., the capacitance-to-digital converter (CDC)–can be the dominant source of energy consumption in the system. Thus, the development of energy-efficient CDCs is crucial to minimizing the energy consumption of capacitive sensor nodes. In the first part of this dissertation, we propose several energy-efficient CDC architectures for low-energy sensor nodes. First, we propose a digitally-controlled coarsefine multislope CDC that employs both current and frequency scaling to achieve significant improvement in energy efficiency. Second, we analyze the limitations of successive approximation (SAR) CDC, and we address these limitations by proposing a robust parasitic-insensitive opamp-based SAR CDC. Third, we propose an inverter-based SAR CDC that achieves an energy efficiency figure-of-merit (FoM) of 31fJ/Step, which is the best energy efficiency FoM reported to date. Fourth, we propose a differential SAR CDC with quasi-dynamic operation to maintain excellent energy efficiency for a scalable sample rate. In the second part of this dissertation, we study the matching properties of small integrated capacitors, which are an integral component of energy-efficient CDCs. Despite conventional wisdom, we experimentally illustrate that the mismatch of small capacitors can be directly measured, and we report mismatch measurements for subfemtofarad integrated capacitors. We also correct the common misconception that lateral capacitors match better than vertical capacitors, and we identify the conditions that make one implementation preferable. In the third and last part of this dissertation, we investigate the potential of novel metal-organic framework (MOF) thin films in capacitive gas sensing. We provide sensitivity-based optimization and simple fabrication flow for capacitive interdigitated electrodes. We use a custom flexible gas sensor test setup that is designed and built in-house to characterize MOF-based capacitive gas sensors.

Orientador: Diogo Paschoalini Volanti / Resumo: O avanço na ciência e tecnologia de sensores de compostos orgânicos voláteis (VOCs) é importante para o desenvolvimento sustentável de materiais funcionais. A dissertação de mestrado refere-se à avaliação do uso de óxido de grafeno (GO, sigla em inglês) em óxido metálicos (OM) tipo-n (V2O5) e tipo-p (Co3O4) para melhorar a sensibilidade, a seletividade e o tempo de resposta dos sensores. O GO teve uma modificação sendo submetido a um processo oxidativo. Os OMs nano ou microestrurados foram preparados a partir de seus sais ou por processos de ressolubilização dos óxidos. Por fim, os compósitos GO-OM foram preparados após os percursores ficarem em suspensão com o GO por 24 horas. O GO aumentou a adsorção gasosa dos compostos resultando em maior seletividade e sensibilidade. Por outro lado, os principais benefícios das estruturas nano e microestrutruradas dos OMs seriam a maior área superficial do material resultando em melhores propriedades gasosas, resultando em mais sítios ativos para adsorção do oxigênio e das moléculas do gás analito. As respostas sensoras foram avaliadas na presença de diferentes concentrações (nas faixas de ppm e ppb) de VOCs (ex.: acetona, acetaldeído, etanol, metanol, benzeno, xileno e tolueno) em atmosfera seca. / Abstract: The advancement in science and technology of volatile organic compounds (VOCs) sensors is essential for the sustainable development of functional materials. The master's thesis refers to the evaluation of the use of graphene oxide (GO) in metallic oxides (OM) type-n (V2O5) and type-p (Co3O4) to improve sensitivity, selectivity and the response time of the sensors. The GO had a modification being subjected to an oxidative process. The nano or microstructured OMs were prepared from its precursors. Finally, the GO-OM composites were prepared after the precursors were in suspension with the GO for 24 hours. The GO increased the gaseous adsorption of the compounds resulting in greater selectivity and sensitivity. On the other hand, the main benefits of the nanostructured and micro-structured structures of OMs would be the greater surface area of the material resulting in better gaseous properties, resulting in more active sites for adsorption of oxygen and analyte gas molecules. The sensory responses were evaluated in the presence of different concentrations (in the ppm and ppb ranges) of VOCs (e.g., acetone, acetaldehyde, ethanol, methanol, benzene, xylene and toluene) in a dry atmosphere. / Mestre

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Increased interest in the field of sensor technology stems from the availability of an inexpensive and robust sensor to detect and quantify the presence of a specific gas. Bulk p-CuO/n-ZnO heterocontact based gas sensors have been shown to exhibit the necessary sensitivity and selectivity characteristics, however, low interfacial CuO/ZnO contact area and poor CuO/ZnO connectivity limits their effective use as gas sensors. The phase equilibria between CuO and ZnO exhibits limited solubility. By exploiting this concept, a CuO/ZnO mixed solution is formed by combining CuO and ZnO precursors using wet chemical (sol-gel) techniques. Thin films fabricated using this mixed solution exhibit a unique CuO/ZnO microstructure such that ZnO grains are surrounded by a network of CuO grains. This is highly beneficial in gas sensing applications since the CuO/ZnO heterostructure interfacial area is considerably increased and is expected to enhance sensing characteristics. This work builds on previous research by Dandeneau et al. (Thin film chemical sensors based on p-CuO/n-ZnO heterocontacts, Thin Solid Films, 2008). CuO/ZnO mixed solution thin films are fabricated using the sol-gel technique and subsequently characterized. X-ray diffraction (XRD) data confirms the phase separation between ZnO and CuO grains. Scanning electron microscopy (SEM) as well as energy dispersive spectroscopy (EDS) reveal a network of ZnO grains amidst a matrix of CuO grains. Optical and electrical characterization provide material parameters used to construct an energy band diagram for the CuO/ZnO heterostructure. Aluminum interdigitated electrodes (IDEs) are patterned on the thin film and gas sensing characteristics in the presence of oxygen and hydrogen are investigated. Optimization of the electrode geometry is explored with the aim of increasing the sensitivity of the sensor in the presence of hydrogen gas. / Graduation date: 2010