Dissertations / Theses on the topic 'Gas sensor'

The detection and monitoring of toxic and explosive gases is often performed using semiconductor gas sensors. The substrate forms an important part of these sensors and current designs were investigated and tested. Various new designs were developed and thick and thin-film technologies employed to fabricate substrates and complete sensors. Substrateless sensors were also analysed and alterations performed to fashion new devices. A number of ceramic materials were tested for their suitability as semiconductor gas sensor substrates. The adhesion of thin-films and thermal conductivity were found to be the most crucial properties, in addition to those typical of ceramics, such as high temperature stability. Alumina is routinely used in semiconductor gas sensors and many other substrates and its performance was compared with less commonly used materials such as beryllia and aluminium nitride. These materials have a much greater thermal conductivity than alumina, and this was shown to improve sensitivity. A semi-empirical formula was derived to enable the prediction of sensitivity loss of a semiconductor gas sensor fabricated on a substrate with high temperature gradients, compared with one where gradients are minimal. The heaters used to raise the temperature of the substrate are typically made from platinum films. The longevity of thin platinum films depends on the film thickness and substrate surface, but for a given film thickness on a given substrate, additional adhesion layers of various metals were also shown to change the films stability and hence lifetime. Various substrate geometries were investigated to optimise temperature distribution and sensitivity. Predominantly subtle effects were observed, but a significant increase of sensitivity was found with an increased surface area. Electrical circuitry used to control and monitor sensors was summarised and a new substrate developed which could be used in conjunction with switching circuitry, the main advantage being that the fabrication of the substrate was more economical than standard substrate configurations.

>Magister Scientiae - MSc<br>The industrial safety requirements and environmental pollution have created a high demand to develop gas sensors to monitor combustible and toxic gases. As per specifications of World Health Organization (WHO) and Occupational Safety and Health Administration (OSHA), lengthy exposure to these gases lead to death which can be avoided with early detection. Semiconductor metal oxide (SMO) has been utilized as sensor for several decades. In recent years, there have been extensive investigations of nanoscale semiconductor gas sensor.

A miniature, ultra-low power, sensitive, microbridge gas sensor has been developed.The heat loss from the bridge is a function of the thermal conductivity of thegas ambient. Miniature thermal conductivity sensors have been developed for gaschromatography systems [1] and microhotplates have been built with MEMS technologywhich operates within the mW range of power [2]. In this work a lower power microbridgewas built which allowed for the amplification of the effect of gas thermalconductivity on heat loss from the heated microbridge due to the increase inthe surface-to-volume ratio of the sensing element. For the bridge fabrication,CMOS compatible technology, nanolithography, and polysilicon surfacemicromachining were employed. Eight microbridges were fabricated on each die,of varying lengths and widths, and with a thickness of 1 μm. A voltagewas applied to the sensor and the resistance was calculated based upon thecurrent flow. The response has been tested with air, carbon dioxide, helium,and nitrogen. The resistance and temperature change for carbon dioxide was thegreatest, while the corresponding change for helium was the least. Thus the selectivity of the sensor todifferent gases was shown, as well as the robustness of the sensor. Another aspect of the sensor is that it hasvery low power consumption. The measuredpower consumption at 4 Volts is that of 11.5 mJ for Nitrogen, and 16.1 mJ forHelium. Thesensor responds to ambient gas very rapidly. The time constant not only showsthe fast response of the sensor, but it also allows for more accuratedetection, given that each different gas produces a different correspondingtime constant from the sensor. The sensor is able to detect differentconcentrations of the same gas as well. Fromthe slopes that were calculated, the resistance change at 5 Volts operation wasfound to be 2.05mΩ/ppm, 1.14 mΩ/ppm at 4.5 Volts, and 0.7 mΩ/ppm at 4 Volts. Thehigher voltages yielded higher resistance changes for all of the gases thatwere tested. Theversatility of the microbridge has been studied as well. Experiments were donein order to research the ability of a deposited film on the microbridge, inthis case tin oxide, to act as a sensing element for specific gases. In thissetup, the microbridge no longer is the sensing element, but instead acts as aheating element, whose sole purpose is to keep a constant temperature at whichit can then activate the SnO film, making it able to sense methane. In conclusion,the microbridge was designed, fabricated, and tested for use as an electrothermalgas sensor. The sensor responds to ambient gas very rapidly with differentlevels of resistance change for different gases, purely due to the differencein thermal conductivity of each of the gases. Not only does it have a fastresponse, but it also operates at low power levels. Further research has beendone in the microbridge's ability to act as a heating element, in which the useof a SnO film as the sensing element, activated by the microbridge, was studied. REFERENCES: 1. D. Cruz,J.P. Chang, S.K. Showalter, F. Gelbard, R.P. Manginell, M.G. Blain," Microfabricated thermal conductivity detector for themicro-ChemLabTM," Sensors andActuators B, Vol. 121 pp. 414-422, (2007). 2. A. G. Shirke, R. E. Cavicchi, S. Semancik, R. H. Jackson, B.G. Frederick, M. C. Wheeler. "Femtomolar isothermal desorption usingmicrohotplate sensors," J Vac Sci TechnolA, Vol. 25, pp. 514-526 (2007).

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.<br>Includes bibliographical references (p. 89-93).<br>Photoacoustic spectroscopy (PAS) is a form of laser spectroscopy that has demonstrated very high sensitivity for gas detection. Typically, PAS involves the absorption of a modulated laser beam by the gas species of interest, and the subsequent generation of acoustic waves at the modulation frequency. The amplitude of the acoustic signal, which can be measured by a microphone, can be amplified by several orders of magnitude with a properly designed gas cell used as an acoustic resonator. In recent times, hollow-core photonic crystal fiber (HC-PCF) has emerged as superior gas cell for standard absorption-based laser spectroscopy due to its small size, compatibility with fiber-based optical components, and easily attainable long light-gas interaction path lengths. However, the possibility of utilizing HC-PCF as a gas cell for PAS has yet to be explored. The size and structure of HC-PCF demands that a new method of PA signal detection must be proposed, because the conventional use of microphones for PAS is not applicable. This thesis describes the development of a proposed novel use of HC-PCF as a PA gas cell from theoretical support to experimental realization. A number of unresolved experimental issues prevented data on the performance of the constructed system from being obtained. These problems are discussed, and recommendations for further study, including several proposed measures to overcome these experimental issues, are made in the conclusion to the thesis.<br>by Raymond Chen.<br>M.Eng.

In an anesthesia machine, there is a need to monitor the anesthesia concentration that is being delivered to the patient, mainly to stop and flush the system in case of fault but also to control the dosage of anesthesia. The infrared sensor with absorption spectrometry technology that Maquet use today is expensive and the desire for a cheaper solution leads to this master thesis. It is possible to determine the proportion of one gas in a gas mixture by using the acoustic properties in a sound wave. This thesis describes an attempt to replace the infrared sensor with an acoustic sensor using ultrasound technology. Modification on an existing acoustic sensor optimized for measuring O2 concentration was done in order to expand its functionality to measure concentration of N2O and different anesthesia drugs. It is observed with the binary gas analyzer developed by Maquet that it is possible to measure O2 concentration with a maximum absolute discrepancy from the built-in Control Gas Analyzer in the FLOW-i anesthesia machine of in air/O2 mixture and in O2/N2O mixture. The concept to measure anesthesia is based on two ultrasound sensors, one placed before the anesthesia vaporizer and the other one is placed after the vaporizer. The sensor placed after the vaporizer will use its measured value as well as the measured fresh gas concentration value from the first sensor to determine the anesthesia concentration. It will inherit the error of the first sensor. However, the error inherited from the first sensor is minimal, since the dynamic range of the sound speed for measuring anesthesia ranging from 0% to 100% is a lot higher than air, O2 and N2O which is the gas compounds that the first sensor measures. Thus the first sensor in the Dual Gas Sampling System has minimal influence on the measured anesthesia concentration. This also means temperature changes on the first sensor that occur because of pressure variation in FLOW-i?s working condition will have minimal effect on the measured anesthesia concentration. Measurement shows that the binary gas analyzer designed as semi side-stream can be fast enough to replace FLOW-i?s Control Gas Analyzer for measuring the fresh gas concentration. The reaction time of the sensor can further be improved if the ultrasound transducers are placed to directly measure in main stream gas flow instead of in a semi side-stream. A modification to the sensor by attaching a thin variable flow restriction that forces the gas flow into the measurement chamber gives an improvement with 10 times shorter rise time for flow rates up to 1 l/min. At higher flow rates, the variable flow restrictor will be pushed open to ease the pressure variation in the measurement chamber. This modification is equal as having the transducers placed in main stream for low flow rate.

This work deals with branch of gas sensors, their construction and methodology of testing. The general aim is a design and implementation of a station for simple testing of conduction gas sensors. The whole station is conceived as virtual measuring apparatus, operated by PC in LabView environment. The station enables mixing of any two gases at concentration demanded and measuring of the basic conduction characteristics of the thick-film and thin-film gas sensors. The central communication interface and modular conception enable easy expansion of possibilities of the whole apparatus in the future. It is possible to measure up to eight gas sensors split into two TO-12 packages simultaneously.

Substantial economic and even safety related gains can be achieved if effective gas turbine performance analysis is attained. During the development phase, analysis can help understand the effect on the various components and on the overall engine performance of the modifications applied. During usage, analysis plays a major role in the assessment of the health status of the engine. Both condition monitoring of operating engines and pass off tests heavily rely on the analysis. In spite of its relevance, accurate performance analysis is still difficult to achieve. A major cause of this is measurement uncertainty: gas turbine measurements are affected by noise and biases. The simultaneous presence of engine and sensor faults makes it hard to establish the actual condition of the engine components. To date, most estimation techniques used to cope with measurement uncertainty are based on Kalman filtering. This classic estimation technique, though, is definitely not effective enough. Typical Kalman filter results can be strongly misleading so that even the application of performance analysis may become questionable. The main engine manufactures, in conjunction with research teams, have devised modified Kalman filter based techniques to overcome the most common drawbacks. Nonetheless, the proposed methods are not able to produce accurate and reliable performance analysis. In the present work a different approach has been pursued and a novel method developed, which is able to quantify the performance parameter variations expressing the component faults in presence of noise and a significant number of sensor faults. The statistical basis of the method is sound: the only accepted statistical assumption regards the well known measurement noise standard deviations. The technique is based on an optimisation procedure carried out by means of a problem specific, real coded Genetic Algorithm. The optimisation based method enables to concentrate the steady state analysis on the faulty engine component(s). A clear indication is given as to which component(s) is(are) responsible for the loss of performance. The optimisation automatically carries out multiple sensor failure detection, isolation and accommodation. The noise and biases affecting the parameters setting the operating point of the engine are coped with as well. The technique has been explicitly developed for development engine test bed analysis, where the instrumentation set is usually rather comprehensive. In other diagnostic cases (pass off tests, ground based analysis of on wing engines), though, just few sensors may be present. For these situations, the standard method has been modified to perform multiple operating point analysis, whereby the amount of information is maximised by simultaneous analysis of more than a single test point. Even in this case, the results are very accurate. In the quest for techniques able to cope with measurement uncertainty, Neural Networks have been considered as well. A novel Auto-Associative Neural Network has been devised, which is able to carry out accurate sensor failure detection and isolation. Advantages and disadvantages of Neural Network-based gas turbine diagnostics have been analysed.

A sensor is a technological device or biological organ that detects, or senses, a signal or physical condition and chemical compounds. Technological developments in the recent decades have brought along with it several environmental problems and human safety issues to the fore. In today's world, therefore, sensors, which detect toxic and inflammable chemicals quickly, are necessary. Gas sensors which form a subclass of chemical sensors have found extensive applications in process control industries and environmental monitoring. The present thesis reports the attempt made in development of Zinc oxide thin film based gas sensors. ZnO is sensitive to many gases of interest like hydrocarbons, hydrogen, volatile organic compounds etc. They exhibit high sensitivity, satisfactory stability and rapid response. In the present work the developed sensors have been tested for their sensitivity for a typical volatile organic compound, acetone. An objective analysis of the various substrates namely borosilicate glass, sintered alumina and hard anodized alumina, has been performed as a part of this work. The substrates were evaluated for their electrical insulation and thermal diffusivity. The microstructure of the gas sensitive film on the above mentioned substrates was studied by SEM technique. The gas sensitive Zinc oxide film is deposited by D.C reactive magnetron sputtering technique with substrate bias arrangement. The characterization of the as-deposited film was performed by XRD, SEM and EDAX techniques to determine the variation of microstructure, crystallite size, orientation and chemical composition with substrate bias voltage. The thesis also describes the development of the gas sensor test setup, which has been used to measure the sensing characteristics of the sensor. It was observed that the ZnO sensors developed with higher bias voltages exhibited improved sensitivity to test gas of interest. Gas sensors essentially measure the concentration of gas in its vicinity. In order to determine the distribution of gas concentration in a region, it is necessary to network sensors at remote locations to a host. The host acts as a gateway to the end user to determine the distribution of gas concentration in a region. However, wireless gas sensor networks have not found widespread use because of two inherent limitations: Metal oxide gas sensors suffer from output drift over time; frequent recalibration of a number of sensors is a laborious task. The gas sensors have to be maintained at a high temperature to perform the task of gas sensing. This is power intensive operation and is not well suited for wireless sensor network. This thesis reports an exploratory study carried out on the applicability of gas sensors in wireless gas sensor network. A simple prototype sensing node has been developed using discrete electronic components. A methodology to overcome the problem of frequent calibration of the sensing nodes, to tackle the sensor drift with ageing, is presented. Finally, a preliminary attempt to develop a strategy for using gas sensor network to localize the point of gas leak is given.

A sensor is a technological device or biological organ that detects, or senses, a signal or physical condition and chemical compounds. Technological developments in the recent decades have brought along with it several environmental problems and human safety issues to the fore. In today's world, therefore, sensors, which detect toxic and inflammable chemicals quickly, are necessary. Gas sensors which form a subclass of chemical sensors have found extensive applications in process control industries and environmental monitoring. The present thesis reports the attempt made in development of Zinc oxide thin film based gas sensors. ZnO is sensitive to many gases of interest like hydrocarbons, hydrogen, volatile organic compounds etc. They exhibit high sensitivity, satisfactory stability and rapid response. In the present work the developed sensors have been tested for their sensitivity for a typical volatile organic compound, acetone. An objective analysis of the various substrates namely borosilicate glass, sintered alumina and hard anodized alumina, has been performed as a part of this work. The substrates were evaluated for their electrical insulation and thermal diffusivity. The microstructure of the gas sensitive film on the above mentioned substrates was studied by SEM technique. The gas sensitive Zinc oxide film is deposited by D.C reactive magnetron sputtering technique with substrate bias arrangement. The characterization of the as-deposited film was performed by XRD, SEM and EDAX techniques to determine the variation of microstructure, crystallite size, orientation and chemical composition with substrate bias voltage. The thesis also describes the development of the gas sensor test setup, which has been used to measure the sensing characteristics of the sensor. It was observed that the ZnO sensors developed with higher bias voltages exhibited improved sensitivity to test gas of interest. Gas sensors essentially measure the concentration of gas in its vicinity. In order to determine the distribution of gas concentration in a region, it is necessary to network sensors at remote locations to a host. The host acts as a gateway to the end user to determine the distribution of gas concentration in a region. However, wireless gas sensor networks have not found widespread use because of two inherent limitations: Metal oxide gas sensors suffer from output drift over time; frequent recalibration of a number of sensors is a laborious task. The gas sensors have to be maintained at a high temperature to perform the task of gas sensing. This is power intensive operation and is not well suited for wireless sensor network. This thesis reports an exploratory study carried out on the applicability of gas sensors in wireless gas sensor network. A simple prototype sensing node has been developed using discrete electronic components. A methodology to overcome the problem of frequent calibration of the sensing nodes, to tackle the sensor drift with ageing, is presented. Finally, a preliminary attempt to develop a strategy for using gas sensor network to localize the point of gas leak is given.

Resistive hydrogen gas sensors based on palladium-hydrogen (Pd-H2) interactions were fabricated and tested. This thesis presents expected resistance characteristics for these sensors, and describes their fabrication process. Test results and analysis identified the H2 sensing mechanisms in these sensors. In particular, linearity between sensor resistance and the approximate atomic hydrogen content in the Pd was established, and the estimated proportionality constant obtained is 2.7± 0.9 (a.u.). A low flow rate sensor test bench featuring a line-switching mechanism was designed and built also. A description of the test bench and its operation principles are discussed. Response times obtained from initial tests of the un-optimized system is 16s ± 9s, comparable to the system response time of a commercial gas sensor test station presently available. Recommendations for future work to optimize this test bench are discussed, as are recommendations for future sensor design and development.<br>Science, Faculty of<br>Physics and Astronomy, Department of<br>Graduate

Sensing BTEX (Benzene, Ethylbenzene, Toluene, Xylene) pollutants is of utmost importance to reduce health risk and ensure public safety. The lack of sensitivity and selectivity of the current gas sensors and the limited number of available technologies in the field of BTEX-sensing raises the demand for the development of high-performance gas sensors for BTEX applications. The scope of this thesis is the fabrication and characterisation of high-quality field-effect transistors (FETs), with functionalised silicon nanowires (SiNWs), for the selective sensing of benzene vs. other BTEX gases. This research addresses three main challenges in SiNW FET-sensor device development: i) controllable and reproducible assembly of high-quality SiNWs for FET sensor devices using the method of dielectrophoresis (DEP), ii) almost complete elimination of harmful hysteresis effect in the SiNW FET current-voltage characteristics induced by surface states using DMF solvent, iii) selective sensing of benzene with up to ppb range of sensitivity using calix[4]arene-derivatives. It is experimentally demonstrated that frequency-controlled DEP is a powerful tool for the selection and collection of semiconducting SiNWs with advanced electrical and morphological properties, from a poly-disperse as-synthesised NWs. The DEP assembly method also leads to a controllable and reproducible fabrication of high-quality NW-based FETs. The results highlight the superiority of DEP, performed at high signal frequencies (5-20 MHz) to selectively assemble only high-quality NWs which can respond to such high DEP frequencies. The SiNW FETs, with NWs collected at high DEP frequencies, have high mobility (≈50 cm2 V-1 s-1), low sub-threshold-swing (≈1.26 V/decade), high on-current (up to 3 mA) and high on/off ratio (106-107). The DEP NW selection is also demonstrated using an industrially scalable method, to allow establishing of NW response characteristics to different DEP frequencies in a very short time window of about 60 seconds. The choice of solvent for the dispersion of the SiNW for the DEP process demonstrates a dramatic impact on their surface trap, with DMF solvent acting as a mild oxidising agent on the NW surface shell. This surface state passivation technique resulted in the fabrication of high-quality, hysteresis-free NW FET transducers for sensor applications. Finally, the proof-of-concept SiNW FET transducer decorated with calix[4]arene-derivative gas receptors exhibits selective detection of benzene vs. other BTEX gases up to 30 ppm concentrations, and up to sub-ppm benzene concentration. The demonstrated NW-sensors are low power and compact, and therefore can be easily mounted on a mobile device, providing instantaneous determination of hazardous gases in the surrounding atmosphere. The methodologies developed in this thesis, have a high potential to make a breakthrough in low-cost, selective gas sensors, which can be fabricated in line with printed and flexible electronic approaches.

The current master's thesis presents the development of a new temperature sensing technology for gas turbine components.The proposed sensor array allows real time simultaneous measurements of temperature at multiple locations, using only two communication leads. Frequency modulation is used to multiplex the signals of more than ten temperature sensors through common wires. At every point of reading, silicon carbide (SiC) microelectronic oscillators generate the required waveforms, at frequencies that are temperature dependent. Those oscillators are fed with a common DC power source, and add their signals together by current addition into the power supply leads.The multiplexed signal can be recorded using only one acquisition channel, and be analyzed in the frequency domain to deduce temperatures.The resulting sensor array can be seen as a temperature sensitive wire, including two leads, and multiple integrated microscopic oscillators. It is compact, and alleviates the problem of lead routing, which is especially cumbersome in small business or regional aircraft engines. SiC microelectronics promising to be operable at temperatures above 700[degrés Celcius], the proposed sensor array could be used inside cooled turbine airfoils and shrouds, in moderate testing and flight cruising conditions, or in compressor components. It offers new possibilities in ground testing, vehicle health monitoring, and engine control. Validation tests were conducted using macroscopic high temperature oscillator prototypes. Two oscillators were built using high temperature discrete components, and were tested in an oven up to 180[degrés Celcius].The results of those tests are presented in this thesis.

Single-walled carbon nanotubes (SWNTs) are nowadays one of the most investigated materials and the realization of ordered SWNT structures is of fundamental importance for the improvement of many technological fields, from the non-linear optics to the realization of transistor, to the assembly of gas sensing devices. A SWNT is formed by rolling a graphene sheet into a seamless cylinder with a diameter on the nanometer scale. The individual SWNTs are joined each other and assembled into bundles by Van der Waals forces. Guest molecules can potentially interact with SWNTs via the outer surfaces of bundles, the inside of the tubes and /or the interstitial channels between the tubes in a bundle. These different situations are expected to play an important role in tuning the guest molecule/SWNT interaction during gas adsorption and/or desorption, and have been investigated theoretically and experimentally using different approaches. In particular, the interaction between gaseous molecules and SWNTs has been investigated from different point of view, including gas storage and gas detection through modification of electronic and thermal properties or through modification of the field emission properties. Compared with conventional solid-state sensors, that typically operate at temperatures over 200 °C, and conducting polymers-based sensors, that provide only limited sensitivity, sensing devices assembled with single-wall nanotubes can exhibit high sensitivity and fast response time at room temperature. Due to the high surface area of nanotubes, a little amount of nanotube material can provide many sites for gas interaction. The accessibility of these sites depends on the status of aggregation of the nanotubes. Our preliminary studies suggested that the sensitivity of a nanotube-based device can be optimized controlling the organization of the SWNTs. Ordered bundles of SWNTs exhibit indeed a sensitivity double with respect to that of a disordered deposit. This is likely due to the enhancement of surface area for organized SWNT systems with respect to randomly placed SWNT bundles. Hence, aligned nanotubes can serve as a very efficient material for use in gas detection. Directionality of SWNT can be obtained directly during the synthesis process, or after manipulation of dispersed nanotubes, by mean of several methods, such as filtration/deposition from suspension in strong magnetic fields, field emission, electrophoresis or dielectrophoretical processes. In particular the use of electric fields to move, position and align SWNTs has been reported in recent papers and the results indicate that both the electrophoresis (EP) and dielectrophoresis (DEP) routes have potential advantages for arranging nanotubes in controlled systems. Beyond the sensitivity, another severe constraint for gas detection is the time either for the reset of the sensor after exposure to the gas, either for the acceleration of the response itself. Since practical applications can be severely limited by slow absorption/desorption processes, we felt it worthwhile to investigate in a systematic way some physical parameters affecting the sensor response. In this thesis we present a study of NH3 ,NOx and H2 detection using organized SWNTs as sensing material and an innovative procedure to improve the time response of the sensor by applying a back gate voltage. Moreover study on gas detection and gas storage were done using QCM sensor.

Els sensors de gasos s’utilitzen per a monitoritzar ambients interiors i exteriors. Algunes aplicacions comuns són per a mesurar el nivell de contaminants als carrers, els gasos alliberats per les fuites industrials i d’automòbils, els gasos a la mineria, el contingut d’alcohol en sang a través de l’alè exhalat, etc. A mesura que creix el camp d’aplicació dels sensors de gasos, es fa necessari adaptar els sensors de gasos als nostres dispositius i pertinences diàries. Es requereixen materials mecànicament flexibles i resistents per a fabricar sensors de gasos flexibles. A banda de proves de detecció de gas, la resistència a la flexió dels sensors ha de provar-se per anomenar “flexible” a un sensor. L’objectiu principal d’aquesta tesi és fabricar sensors de gasos flexibles mitjançant processos additius emprant òxids metàl·lics com a materials sensibles. Els sensors de gasos flexibles es varen fabricar utilitzant un substrat polimèric flexible (Kapton). Els diferents processos emprats varen ser compatibles amb la temperatura de funcionament del substrat. Entre les tècniques emprades estan la plantilla, la serigrafia, la injecció de tinta, AA-CVD. A més a més, es varen realitzar processos superficials per a millorar l’adhesió dels òxids metàl·lics al substrat polimèric. La flexibilitat dels sensors es va provar realitzant una prova de flexió cíclica.<br>Los sensores de gas se utilizan para monitorear ambientes interiores y exteriores. Algunas aplicaciones comunes son para medir: el nivel de contaminantes en las calles, los gases liberados por los escapes industriales y de automóviles, los gases en la minería, el contenido de alcohol en la sangre a través del aliento exhalado, etc. A medida que crece el campo de aplicación de los sensores de gas, se hace necesario adaptar los sensores de gas a nuestros dispositivos y pertenencias diarias. Se requieren materiales mecánicamente flexibles y resistentes para fabricar los sensores de gas flexibles. Además de las pruebas de detección de gas, la resistencia a la flexión de los sensores debe probarse para llamar “flexible” a un sensor. El objetivo principal de esta tesis es fabricar sensores de gas flexibles a través de procesos aditivos utilizando óxidos metálicos como materiales sensibles. Los sensores de gas flexibles se fabricaron utilizando un sustrato polimérico flexible (Kapton). Los diferentes procesos empleados fueron compatibles con la temperatura de la temperatura de funcionamiento del sustrato. Entre las técnicas empleadas están la plantilla, la serigrafía, la inyección de tinta, AA-CVD. Además, se realizaron procesos superficiales para mejorar la adhesión de los óxidos metálicos al sustrato polimérico. La flexibilidad de los sensores se probó realizando una prueba de flexión cíclica.<br>Gas sensors are used to monitor indoor and outdoor environments. Some common applications are to measure: the level of pollutants in the streets, the gases liberated by industrial and car exhausts, gases in mining, blood alcohol content through the exhaled breath, etc. As the field of application for gas sensors is growing, it becomes necessary to adapt the gas sensors to our daily devices and belongings. This requires mechanically flexible and resistant materials to fabricate the flexible gas sensors. In addition to gas sensing tests, the resistance to bending of the sensors should be tested to call a sensor flexible. The main objective of this thesis is to fabricate flexible gas sensors through additive processes using metal oxides as sensitive materials. The flexible gas sensors were fabricated using a flexible polymeric substrate (Kapton). The different processes employed were compatible with the temperature of the operating temperature of the substrate. Among the techniques employed are stencil, screen-printing, inkjet-printing, AA-CVD. Also, surface processes were performed to improve the adhesion of the metal oxides to the polymeric substrate. The flexibility of the sensors was tested by performing a cyclical bending test.

Holographic sensors are photonic layered structures contained in analyte sensitive lms that upon illumination produce monochromatic reflections (λ). The present work reports the fabrication of oxygen and ammonia sensors in Nafi on membranes and hydrocarbon and volatile organic compound sensors in poly(dimethylsiloxane) (PDMS) films. A holographic recording technique was developed to suit these materials consisting of the in situ formation of nanoparticles of 18nm average diameter and their subsequent ordered ablation with a 300mJ laser. The wavelength of the monochromatic reflections depends principally on the refractive index of the resulting layers (n) and the separation between them (Λ). Changes in these parameters are generated by the analyte-sensor interactions and their magnitude can be correlated to the analyte concentration. The strength of these interactions is determined by the thermodynamic properties of the analytes, such as the cohesive energy density (δ^2), and this, was coupled with a photonic model for the prediction of the holographic response. After exposure to different concentrations of the analytes, the kinetics of the responses were determined and the lowest detection limits (LDL) established as follows: Hydrocarbons in PDMS holograms 1% (v/v) in 3s for a range of concentrations from 0-100%; ammonia in Nafi on holograms 0.16% in 100s in the 0-12.5% range; the LDL for oxygen sensing could not be determined although the response was recorded down to 12.5% and up to 100% in 100s. Holographic sensors show competitive responses comparable to commercially available gas sensors for biomedical diagnostics and industrial process monitoring because of their facile fabrication and their shared sensing platform allowing multiplexing.

This dissertation describes the fabrication and operation of porous silicon gas sensors. The first chapter describes the motivation behind gas sensor research and provides the reader with background knowledge of gas sensors including the terminology and a review of various gas sensors. The following two chapters describe both how the porous silicon gas sensors are created and how they have been tested in the laboratory. Chapter 4 describes the steps required to create arrays of gas sensors to provide for a selective device through the application of patented selective coatings. Chapter 5 proposes a physical model that leads to a numerical solution for predicting the operation of the gas sensor. The next chapter builds from this model to analyze and optimize the experimental methods that are used to test both this and other gas sensors. The final chapter of this dissertation describes the prototype gas sensor system that has most recently been created, the company that was formed to further the development of that system, and the future applications of the porous silicon gas sensor.

A fundamental limitation of many chemically sensitive organic semiconductor materials is their high susceptibility to cross-interference resulting from interactions with background species other than those actively being detected. Such cross-sensitivities often preclude their use in 'real' sensor applications, particularly where discrete and selective gas sensing systems are required. It has been hypothesised, however, that this lack of specificity can largely be overcome with the adoption of a multi-element sensor array, thereby allowing the compensation of unwanted sensitivities through suitable signal processing. This thesis describes how such a multi-element sensor array of different gas sensitive metallophthalocyanine films, constructed on a single substrate, was used as the sensing element in an 'intelligent' chemical sensor. Since the individual sensors show varying degrees of gas sensitivity, the individual responses of each to any particular analyte will give rise to a characteristic change in the output 'pattern' comprised of each of the sensor resistances. By monitoring the change in this pattern of responses on exposure to specific gases of pre-determined concentration and employing a suitable feature extraction algorithm, the characteristic responses to particular analytes was learnt, and a knowledge base, from which future inferences may be drawn, was constructed. The success of suitable signal processing techniques to accommodate the inherent cross-sensitivities exhibited by these materials is demonstrated. The results demonstrate the viability of pattern recognition methods to analyse gas mixtures by comparing particular features of the combined array response with those previously learnt during a gas recognition training phase.

<p>A novel MOSFET gas sensor for the investigation has been developed. Its configuration resembles a"normally on"n-type thin-film transistor (TFT) with a gas sensitive metal oxide as a channel. The device used in the experiments only differs from common TFTs in the gate configuration. In order to allow gas reactions with the SnO2-surface, the gate is buried under the semiconducting layer. Without any gate voltage, the device works as a conventional metal oxide gas sensor. Applied gate voltages affect the channel carrier concentration and surface potential of the metal oxide, thus causing a change in sensitivity. The results of the gas measurements are in accordance with the electric adsorption effect, which was postulated by Fedor Wolkenstein 1957, and arises the possibility to operate a semiconductor gas sensor at relatively low temperatures and, thereby, be able to integrate CMOS electronics for processing of measurements at the same chip.</p>

<p>Gas sensors are today used in many different application areas, and one growing future market is battery operated sensors. As many gas sensor components are heated, one major limit of the operation time is caused by the power dissipated as heat. AppliedSensor is a company that develops and produces gas sensor components, modules and solutions, among which battery operated gas sensors are one targeted market.</p><p>The aim of the diploma work has been to simulate the heat transfer on a hydrogen gas sensor component and its closest surroundings consisting of a carrier mounted on a printed circuit board. The component is heated in order to improve the performance of the gas sensing element.</p><p>Power dissipation occurs by all three modes of heat transfer; conduction from the component through bond wires and carrier to the printed circuit board as well as convection and radiation from all the surfaces. It is of interest to AppliedSensor to understand which factors influence the heat transfer. This knowledge will be used to improve different aspects of the gas sensor, such as the power consumption.</p><p>Modeling and simulation have been performed in FEMLAB, a tool for solving partial differential equations by the finite element method. The sensor system has been defined by the geometry and the material properties of the objects. The system of partial differential equations, consisting of the heat equation describing conduction and boundary conditions specifying convection and radiation, was solved and the solution was validated against experimental data.</p><p>The convection increases with the increase of hydrogen concentration. A great effort was made to finding a model for the convection. Two different approaches were taken, the first based on known theory from the area and the second on experimental data. When the first method was compared to experiments, it turned out that the theory was insufficient to describe this small system involving hydrogen, which was an unexpected but interesting result. The second method matched the experiments well. For the continuation of the project at the company, a better model of the convection would be a great improvement.</p>

Gas sensing in medical applications requiresmall, precise and sensitive sensors. This projecthas developed a laboratory setup for characterisationof a waveguide-based gas sensor for carbon dioxide andmethane working in the mid-IR range of 2 - 10 μm. Thissetup utilizes an IR-camera to image the waveguideswhen a mid-IR laser is coupled into them. Along thelaboratory work, a program for optimisation of waveguidelength has been made and a study of on-marketmedical carbon dioxide sensors has been done. Thelaboratory setup shows potential for good measurementof waveguide losses, but several problems was identifiedwith the measurement methods currently used. Fromthe sensor study, the standard performance for currentsensors is presented as well as areas where gas sensorscould be improved. Size, speed and accuracy were someof the characteristics a waveguide-based sensor couldimprove on and open up for new sensor application in,for example, hand-held medical devices.

The mineral processing group of McGill University developed a novel gas holdup probe that consists of two conductivity flow cells: an open cell used to estimate dispersion (slurry + air) conductivity and a syphon cell used to estimate slurry conductivity. These two values are entered into Maxwell's model to calculate gas holdup.<br>In this work some design criteria for conductivity flow cells and the syphon cell are given. Effect of geometrical cell constant and electrode width on cell behaviour are analyzed. New dimensions for open and syphon cells are proposed. Conditions to prevent bubbles from being entrained into the syphon cell are established.<br>The new design of the gas holdup probe was tested successfully over a prolonged period at the INCO Matte Separation Plant (Copper Cliff, Ontario). Tests carried out in waste paper de-inking at BOWATER (Gatineau, Quebec) showed the gas holdup values given by the probe agreed with the values obtained from pressure. The noise associated with the gas holdup signal obtained by the probe could be used to diagnose sparger operation.<br>Gas holdup showed some degree of correlation with flotation efficiency of waste paper de-inking and flotation rate constant. Chemistry and rheology of the feed are other factors to be considered. Estimation of bubble surface area flux should consider rheology properties (liquid viscosity and density).

There has been an increasing demand of hand held battery operated gas monitors because of their widespread applications. However, the existing gas sensors suffer from high power consumption (> 100 mW) and most of them are not CMOS compatible, thus expensive. The aim of this research is to develop a smart micro-hotplate platform for high temperature gas sensor application. The gas sensor devices should consume low power and be fully CMOS compatible. This will enable the monolithic integration of interfacing circuitry with the sensor device on the same chip and thus will make the device performance more reliable and reproducible. The work mainly focused on two aspects: (i) design and development of low power reliable micro-hotplates and (ii) design and integration of intelligent electronic interface for the amplification and read out of the gas sensing signal. The design and simulation were carried out in Cadence and ANSYS software. The devices were fabricated in two batches in XFAB, Germany. Both aluminium and tungsten metallization were used. Tungsten was used to avoid electro migration at high temperature. The first batch was a proof of concept batch, which contains mostly discrete micro-hotplates; whereas electronic integration was the main focus on the second batch. The micro-hotplate contains MOSFETs as the heating elements. The heaters are embedded in thin SOI membrane. The membranes were realized using DRIE technique in Silex, Sweden. The electro-thermal and optical characterisation of the micro-hotplates shows that the membranes are very stable. The devices measured on different positions and wafers show excellent reproducibility. The MOSFET micro-heaters survived temperatures above 500° C. The hotplates consumed low power, operating temperature up to 550° C was achieved at a power cost of only 16 mW, which is much lower than the present gas sensors. The sensing material in the form of a CNT layer was grown on the micro-hotplates (using local growth technique) and the preliminary gas testing results showed lots of promise.

L'objectif de ce projet est d'explorer la possibilité d’utiliser des oxydes mixtes nanostructurés obtenus par broyage à haute énergie (HEBM en anglais) dans des capteurs de gaz des oxydes mixtes à haute performance et à faible coût. Les compositions chimiques, LaFeO3 et LaCoO3, ont été choisies en fonction de leurs propriétés intrinsèques de détection de gaz proposées dans la littérature. L'effet des paramètres de synthèse sur leurs performances de détection de gaz a été étudié. Ce projet est divisé en trois étapes. Dans la première étape, les paramètres de synthèse ont été optimisés pour obtenir des oxydes nanocristallins LaCoO3 à structure pérovskite. Un procédé de revêtement a ensuite été développé afin de déposer le matériau sous forme de poudre sur un substrat électriquement résistant et de créer un dispositif de détection. Cette méthode consiste en une simple étape d’enrobage où la poudre nanocristalline est mise en suspension dans une solution aqueuse à un pH ajusté avec précision et le substrat y est immergé jusqu'à l’obtention d’une couche continue et homogène. Les échantillons ont été ensuite séchés, conditionnés et les propriétés de détection ont été évaluées en mesurant essentiellement le comportement de la résistance électrique sous différentes compositions de gaz. Afin de comparer la méthode de fabrication des oxydes dans ce projet (broyage à boulets, BM) à d'autres méthodes de synthèse classiques, les mêmes compositions chimiques des pérovskites LaFeO3 et LaCoO3 ont été réalisées par la méthode sol-gel (SG) et par réaction à l’état solide (SSR). L'effet de la taille des particules sur les performances de détection du monoxyde de carbone par le LaCoO3 a été étudié. En comparant aux autres méthodes classiques, la technique par broyage à haute énergie a abouti à la plus petite taille des cristallites, environ 11 nm, alors que la SG et la SSR ont donné une taille de cristallites respectivement de 20 nm et 1 μm. Le taux de réponse maximale vis-à-vis au CO a été augmenté de 7% pour les échantillons par SSR à 17% pour la SG et jusqu’à 26% pour la BM, tout en conservant une surface spécifique stable pour les trois méthodes de synthèse. Dans la deuxième étape, la surface spécifique (SSA) des échantillons broyés par BM a été augmentée en utilisant une seconde étape de broyage. L'effet de la surface spécifique sur les performances de détection de gaz et sur la mobilité des atomes d'oxygène ainsi que sur leur capacité de désorption des oxydes mixtes a été examiné. Les matériaux synthétisés ont été caractérisés par diffraction des rayons X (XRD), par désorption du dioxygène à température programmée (TPD-O2) et par analyse de leur surface spécifique (BET). Les résultats de détection ont révélé l’effet positif d’une faible taille de cristallites associée à une grande surface spécifique sur les performances de détection de gaz. La surface spécifique de l'échantillon synthétisé par BM est passée de 4 m2/g à une valeur optimale de 66 m2/g grâce à la seconde étape de broyage. La pérovskite optimisée par deux étapes de broyage a montré le plus fort taux de réponse allant jusqu'à 75% pour 100 ppm de CO dans l'air sec à 125°C. Ce pourcentage est de quatre à dix fois supérieur à ceux obtenus par sol-gel et par réaction à l'état solide. La performance de détection de gaz du composé LaCoO3 ayant une taille de cristallites de 11 nm et une surface spécifique de 66 m2/g a été définie comme étant le matériau de référence pour d'autres améliorations. Dans la troisième étape, le potentiel de la méthode de BM dans l’obtention de composés chimiques dopés a été exploré par la synthèse de formulations ayant la forme La1-xCexCoO3 où le pourcentage de cérium et l'effet de ce dopage sur les propriétés de détection de gaz ont été évalués. L'effet de l'élément dopant sur la structure pérovskite a été étudié. Les composés dopés par le cérium ont montré un point de saturation de 10% dans la structure pérovskite et un ajout supplémentaire de Ce à ce pourcentage limite entraîne l’apparition de l'oxyde de cérium en tant qu'impureté et affecte la détection des gaz. La température de détection optimale du CO pour la formulation dopée a été trouvée à 100°C par rapport à 130°C pour la structure pérovskite de référence (LaCoO3). Parmi les oxydes mixtes dopés au Ce, la formulation La0.9Ce0.1CoO3 montre le meilleur taux de réponse (240%) qui est de quatre fois supérieur au taux de réponse du LaCoO3 pour une même concentration de CO. La TPD-O2, la TPD-CO et l’analyse de surface XPS ont été effectuées pour établir la relation entre la performance de détection et les propriétés physiques et chimiques des échantillons synthétisés. En outre, les pérovskites nanostructurées de la forme LaFeO3 ont également été synthétisées en utilisant la méthode HEBM. Cette formulation a été choisie pour sa sensibilité intrinsèque et pour sa capacité de détection du CO. Les propriétés de détection de cette formulation pour le méthane sont améliorées par un dopage au palladium. L’oxyde de Pd est imprégné sur la surface de l’oxyde nanostructuré LaFeO3. Ce dopage révèle l'effet de ce métal noble sur les performances de détection au méthane. Différentes masses d’oxyde de Pd ont été utilisées pour déterminer la quantité optimale à ajouter afin de maximiser la détection du méthane. Les composés nanostructurés dopés au Pd indiquent une bonne sensibilité au méthane à très basse température (<150°C), alors que pour la pérovskite pure de LaFeO3, la détection est inexistante dans cette gamme de température. Un pourcentage massique de 2% Pd pour le composé LaFeO3 montre un taux de détection maximum de 600% par rapport aux 300 ppm CH4 dans l'air. Cet oxyde dopé possède une taille de cristallite de 14 nm et une surface spécifique élevée de 46 m2/g. La capacité de stockage du méthane de la formulation dopée a été également évaluée en étudiant l'effet de l'élément de dopage sur la capacité d'adsorption et de sa relation avec la performance de détection d'échantillons synthétisés. Aucune activité catalytique n’a été observée pour les formulations dopées au Pd.<br>The aim of this project is to explore the possibility of exploitation of nanostructured mixed oxides obtained by HEBM technique in development of high efficient gas sensors in terms of performance and cost. LaFeO3 and LaCoO3 formulations were chosen as perovskite-based materials, based on their intrinsic sensing properties reported on the literature, to investigate the effect of synthesis parameters on their gas sensing performance. In the first step, synthesis parameters were optimized to obtain nanocrystalline LaCoO3 perovskite-oxide. A coating method was then developed in order to coat the sensing material in powder form on an electrically resistant substrate and to provide a sensing device. This coating method consisted of a simple wash-coating process where the nanocrystalline powder is put in suspension in an aqueous solution with an accurately adjusted pH and the substrate is dipped in until a continuous and homogeneous thick sensing layer is formed. The samples were then dried and conditioned and the sensing properties were evaluated basically by measuring electrical resistance behaviour of the device in different gas compositions. In order to compare the ball milling (BM) method with other synthesis methods, the same formulation was also obtained using sol-gel (SG) and solid-state reaction (SSR) methods. The effect of crystallite size on CO sensing performance of synthesized LaCoO3 was studied. Compared to the other methods, HEBM resulted in lowest crystallite size of 11 nm while the SG and SSR gave a crystallite size of 20 nm and 1 µm, respectively. While the specific surface area of all samples remained similar, the maximum response ratio was increased from 7% for SSR samples to 17% and 26% for SG and BM samples, respectively. In the second step, specific surface area (SSA) of milled materials was increased using a second milling process. The new synthesis process was called Activated Reactive Synthesis (ARS). The effect of surface area on gas sensing performance and oxygen mobility as well as oxygen desorption capacity of synthesized materials was investigated. Synthesized materials were characterized using XRD, TPD-O2 and BET. Gas sensing results revealed a positive effect of low crystallite size and high surface area on gas sensing performance of milled materials. Specific surface area of the BM sample was successfully increased from 4 m2/g to an optimum value of 66 m2/g by an ARS step. Improved BM material showed the highest response ratio of up to 75% for 100 ppm CO in dry air at 125°C, which is four and ten times higher than those obtained by sol-gel and solid-state reaction methods, respectively. The gas sensing performance of LaCoO3 samples with a crystallite size of 11 nm and a specific surface of 66 m2/g was set as a benchmark for further improvements. In the third step, the potential of ARS method in providing the doped formulations was explored by synthesizing La1-xCexCoO3 series doped with different amounts of cerium. The effect of cerium doping on perovskite structure and its gas sensing properties was then evaluated. Ce-doped formulations showed a saturation point at 10 at.% in the perovskite structure. The optimum CO sensing temperature for doped formulation was found to be 100°C compared to 130°C for pure perovskite. Among the Ce-doped formulations, La0.9Ce0.1CoO3 showed the best response ratio (240%) with respect to 100 ppm CO that was four times higher than the response ratio of pure LaCoO3. TPD-O2, TPD-CO and XPS were performed to find the relation between sensing performance and physical and chemical properties of synthesized samples. Further addition of Ce resulted in segregation of cerium oxide as a second phase (impurity) and deteriorated the sensing performance of the doped materials. Nanostructured LaFeO3 perovskite was also synthesized using ARS method. This formulation was chosen for its intrinsic hydrogen and CO sensing properties. The sensing properties of this formulation with respect to methane were improved by Pd doping. Pd oxide was impregnated on the surface of nanostructured and high surface of LaFeO3 to further enhance its methane sensing performance. Different amounts of palladium oxide were used to find the optimum level of doping. Doped formulations showed a good sensitivity to methane at very low temperature (<150°C) while pure LaFeO3 did definitely not show any sensing property with respect to methane at the same temperature range. LaFeO3 with 2 wt.% Pd with a crystallite size of 14 nm and a high specific surface area of 46 m2/g showed maximum response ratio of 600% with respect to 300 ppm CH4 in air. Methane storage capacity of doped formulation was evaluated to investigate the effect of doping element on adsorption capacity and its relation with the sensing performance of synthesized samples. No catalytic activity was observed for doped formulations.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO<br>COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR<br>CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO<br>PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO<br>PROGRAMA DE EXCELENCIA ACADEMICA<br>Neste trabalho foi obtido um sensor de gás baseado no grafeno crescido por CVD. Amostras foram transferidas usando o polímero Poliuretano (PU) como camada de sacrifício, sendo confirmada a eficácia do método proposto quando comparado com aqueles existentes na literatura. Foi confirmada a qualidade do filme monocamada transferido mediante o controle dos defeitos gerados durante a transferência e a fabricação do dispositivo. Foram depositados sobre o grafeno contatos na forma de um circuito interdigitado e estudada a mudança da resistência do sensor construído para gases de NO2 e NH3. Espectroscopia Raman foi usada também neste trabalho para investigar o impacto da densidade dos defeitos no filme de grafeno na resposta do sensor de gás. O dispositivo proposto foi capaz de detectar baixas concentrações dos gases alvo testados.<br>In this work a gas sensor based on graphene grown by CVD was obtained. Samples were transferred using Polyurethane (PU) polymer as the sacrificial layer, and the ecacy of the proposed method was confirmed when compared with those in the literature. The quality of the transferred monolayer film was confirmed by controlling the defects generated during the transfer and fabrication of the device. Contacts were deposited on top of the transferred film in the form of an interdigitated circuit and the sensor s resistance evolution was studied in the presence of NO2 and NH3. Raman spectroscopy was also used to investigate the impact of graphene defects density on the gas sensor response. The proposed device was able to detect low concentrations of the tested target gases.

In this thesis a cyber-physical system for gas sensor measurements was constructed. In the design implementation, two different approaches were taken; we created a device for calibrating and testing the sensors and another device acting as independent battery-powered measurement platform. Both systems are compatible with a separate circuit (sensor)board coupled within the sensors. This board supports both commercial Taguchi-type and custom sensors. In addition, the circuit (sensor)board includes optional heater circuits for gas sensors as well as a separate temperature and humidity sensor. The devices utilize Arduino-based microcontrollers and a Raspberry Pi single board computer which were programmed to execute the specified functions. According to the nature of cyber-physical system, devices are able to save the data to a memory card and upload it to internet using the selected cloud service. In order to validate the specified functionality of the devices, gas sensors were fabricated by inkjet-printing platinum decorated tungsten(VI) oxide nanoparticles onto a substrate. The substrate was then wire bonded to a dual in-line package-compatible chip carrier. Test measurements and sensor calibration were carried out in a custom test chamber in hydrogen gas environment<br>Tässä työssä valmistettiin kyberfyysinen järjestelmä kaasusensorimittauksille. Suunniteltu toteutus sisältää kaksi lähestymistapaa; yksi laite sensoreiden kalibrointiin ja testaukseen sekä toinen akkukäyttöinen, itsenäisenä mittausalustana toimiva laite. Sensorit sijoitettiin erilliselle piirilevylle joka oli yhteensopiva molempien järjestelmien kanssa. Tämä sensorikortti tukee sekä kaupallisia Taguchi-tyyppisiä sensoreita että itsetehtyjä sensoreita. Se sisältää myös valinnaiset lämmityspiirit kaasusensoreille sekä erillisen lämpötila- ja kosteussensorin. Laitteet hyödyntävät Arduino-pohjaisia mikrokontrollereita sekä Raspberry Pi -pienoistietokonetta jotka ohjelmointiin toteuttamaan vaaditut toiminnot. Noudattaen kyberfyysisien järjestelmien luonnetta laitteet tallentavat mittausdatan muistikortille ja lähettävät datan valittuun pilvipalveluun. Toiminnallisuuden todentamiseksi valmistettiin kaasusensoreita platinalla päällystetyistä wolframitrioksidi -nanopartikkeleista. Partikkelit tulostettiin substraatille mustesuihkutulostimella ja lankabondattiin dual in-line package-yhteensopivaan välikappaleeseen. Mittaukset tehtiin erikoisvalmisteisessa testikammiossa vetykaasussa

碩士<br>國立屏東科技大學<br>材料工程所<br>95<br>Abstract Student ID：M9440007 Title of Thesis：The Gas Sensing Properties of Formaldehyde Gas Sensor Total Pages：67 Name of Institute：National Ping-Tung University of Science & Technology Name of Department：Department of Materials Engineering Date of Graduation：2007.07 Degree Conferred：Master Name of Student：Yan-Ting Wu Adviser：Lung-Ming Fu, Chia-Yen Lee The Contents of Abstract in this Thesis: The purpose of this study is to design and develop semiconductor-type Formaldehyde Gas Sensor by MEMS. This sensor is suitable not only for industrial process monitoring, but also for the detection of formaldehyde concentrations in buildings in order to act as the safeguard of the human’s health condition. In the present study, the glass substrate is used as a base, then upon this base, a sensing layer, a heating device and IDEs are integrated. The integrated micro-hotplates in the proposed design provide an instantaneous and precise temperature control capability. The current experimental results show that applied voltage of 5.2W yields a constant temperature of 300 ◦C. The range of formaldehyde detected of 40 to 8600 ppb that the time response of the gas sensor developed in the present study. The average time constant of the proposed formaldehyde gas sensor is determined to be 70s for formaldehyde concentrations in the range 0–3 ppm at a micro-hotplate temperature of 300 ◦C. The recovery time of the proposed formaldehyde gas sensor is determined to be 80s that sensitivity of 0.47kΩ/ppb at 300℃and a detection limit below 800ppb. The purpose of this study is to obtain the better sensitivity and the minimal monitoring concentration. The result of this experiment presented the difference of resistance of sensing layer is proportion to the concentration of formaldehyde. Keywords: formaldehyde, micro hotplate, NiO thin film, co-sputter

Thesis (M.S.)--State University of New York at Buffalo, 2006.<br>Title from PDF title page (viewed on Mar. 09, 2007) Available through UMI ProQuest Digital Dissertations. Thesis adviser: Wobschall, Darold C. Includes bibliographical references.

The design of a photonics-based multi-gas sensor is presented. Absorption spectroscopy theory has been analyzed to derive key requirements for effective gas concentration measurements. HITRAN spectral analyses have determined appropriate ranges for single and multi-gas sensing. A discussion of two setups (large-scale setup and portable prototype) outlines relevant results for the development of innovative data processing algorithms (floating-point technique (FPT)). Eight absorption lines were experimentally detected (761 nm range), facilitating the recognition of oxygen spectra with surety. The FPT was used to measure oxygen concentration with an approx. 2.5% error when scanning one absorption line. Strategies to reduce the error to below 0.1% and to improve the prototype are presented. The sensor is expected to operate in an inhomogeneous network. The network utilizes different sensors capable of cross-using information to achieve high reliability and accuracy, in order to predict, prevent, and recognize man-made and natural threats.

碩士<br>國防大學中正理工學院<br>應用化學研究所<br>94<br>This research is regarding platinum-ruthenium alloy as and detecting catalysts, that will detect catalysts and add the deionized water to mix into the electrode thick liquid material . This experiment is divided into two stages: 1.The discussion of treatment before the catalyst, 2. Analysis of the behavior that the electrode is detected to the gas. Deal with some before the catalyst, by way of different mixing separately, add different dispersant and thickness of the dispersant as the parameter, analyse catalysts to disperse and stabilize the situation with Laser Light Scattering system Zeta Plus and Rheometry ; in addition, in the electrode on detecting analysing to the gas, probe into and analyse that detects the detecting and examining to carbon monoxide of electrode by making the law of electric potential. The experimental result shows , the platinum-ruthenium alloy electrode presents the linear relations to detecting the electric current and concentration of carbon monoxide. In addition, detecting electrodes under the circumstances that the optimum condition is made, the best initial time is 10 seconds, response time expires by 50 to 60 seconds, can obtain the best sensitivity of detecting and can be examined for the 4.14 μA/ppm and the minimum concentration of limit to 25 ppm .

Current gas sensor technology, although meeting the minimum requirements in many instances, suffers for a number of limitations. Hence, there is currently a considerable volume of research being undertaken at many laboratories of different countries. In the past, all chemical sensors and catalyst were optimized empirically by a trial and error method. Today, however, systematic research and development is becoming increasingly important in order to improve sensors and to find new sensing principles. Obtaining a long term stable gas sensor with improved sensitivity, selectivity, and low cost for mass production passes through fundamental research and material characterization to build new chemically sensitive devices or to improve existing ones. The bottom line in the design and manufacture of modern gas sensors is the transfer from ceramic(of Figaro type) to thin film gas sensors(TFGs). This transfer provides new opportunities for further microminiaturization, power consumption and cost reduction of gas sensors. Therefore, at the present time, thin film gas sensors are the basis for the design of the modern gas sensitive multi-parameter microsensor systems. Applications of these systems include environment, security, home systems, smart buildings, transportation, discrete manufacturing, process industries and so on. Microelectromechanical systems(MEMS) based integrated gas sensors present several advantages for these applications such as ease of array fabrication, small size, and unique thermal manipulation capabilities. MEMS based gas sensors; which are usually produced using a standard CMOS(Complimentary Metal Oxide Semiconductor) process, have the additional advantages of being readily realized by commercial foundries and amenable to the inclusion of on-chip electronics. In order to speed up the design and optimization of such integrated sensors, microheater designs for gas sensor applications have been presented as first part of the present thesis. As heater design is the key part for a gas sensor operation. So 3D simulations have been used to optimize micro-heater geometry. The application of MEMS Design Tool(COVENTORWARE) has been presented to the design and analysis of micro-hotplate (MHP) structures. Coupled Electro-thermal analysis provided an estimation of thermal losses and temperature distribution on the hotplate for realistic geometrical and material parameters pertinent to fabrication technology. Five microheater designs have been proposed in terms of different sizes and shapes in order to optimize the microhotplate structure to be used for gas sensor operation for the specified range of temperature and power consumption. To produce a gas sensor, which is able to detect LPG leak, thin films of tin oxide have been developed. FR sputtering has been used to deposit gas sensitive tin oxide thin filmls under various deposition conditions. Four different values of pressure in the range from high pressure(5 X 10-2 mbar) to lower pressure (2 X 10-3 mbar), three RF power values 50, 75, 100 W and varied oxygen percentage in sputtering atmosphere (0-18%) have been used to optimize the material properties of tin oxide thin films to study the sensitivity towards LPG. All the samples have been analyzed using various macro and microscopic characterization techniques. Extensive studies have been done on the sensor response for the samples deposited under different conditions. Finally the sample film deposited at 5 x 10-3 mbar, with applied power of 75 W in the presence of 8% oxygen, showed maximum sensitivity towards LPG.

Current gas sensor technology, although meeting the minimum requirements in many instances, suffers for a number of limitations. Hence, there is currently a considerable volume of research being undertaken at many laboratories of different countries. In the past, all chemical sensors and catalyst were optimized empirically by a trial and error method. Today, however, systematic research and development is becoming increasingly important in order to improve sensors and to find new sensing principles. Obtaining a long term stable gas sensor with improved sensitivity, selectivity, and low cost for mass production passes through fundamental research and material characterization to build new chemically sensitive devices or to improve existing ones. The bottom line in the design and manufacture of modern gas sensors is the transfer from ceramic(of Figaro type) to thin film gas sensors(TFGs). This transfer provides new opportunities for further microminiaturization, power consumption and cost reduction of gas sensors. Therefore, at the present time, thin film gas sensors are the basis for the design of the modern gas sensitive multi-parameter microsensor systems. Applications of these systems include environment, security, home systems, smart buildings, transportation, discrete manufacturing, process industries and so on. Microelectromechanical systems(MEMS) based integrated gas sensors present several advantages for these applications such as ease of array fabrication, small size, and unique thermal manipulation capabilities. MEMS based gas sensors; which are usually produced using a standard CMOS(Complimentary Metal Oxide Semiconductor) process, have the additional advantages of being readily realized by commercial foundries and amenable to the inclusion of on-chip electronics. In order to speed up the design and optimization of such integrated sensors, microheater designs for gas sensor applications have been presented as first part of the present thesis. As heater design is the key part for a gas sensor operation. So 3D simulations have been used to optimize micro-heater geometry. The application of MEMS Design Tool(COVENTORWARE) has been presented to the design and analysis of micro-hotplate (MHP) structures. Coupled Electro-thermal analysis provided an estimation of thermal losses and temperature distribution on the hotplate for realistic geometrical and material parameters pertinent to fabrication technology. Five microheater designs have been proposed in terms of different sizes and shapes in order to optimize the microhotplate structure to be used for gas sensor operation for the specified range of temperature and power consumption. To produce a gas sensor, which is able to detect LPG leak, thin films of tin oxide have been developed. FR sputtering has been used to deposit gas sensitive tin oxide thin filmls under various deposition conditions. Four different values of pressure in the range from high pressure(5 X 10-2 mbar) to lower pressure (2 X 10-3 mbar), three RF power values 50, 75, 100 W and varied oxygen percentage in sputtering atmosphere (0-18%) have been used to optimize the material properties of tin oxide thin films to study the sensitivity towards LPG. All the samples have been analyzed using various macro and microscopic characterization techniques. Extensive studies have been done on the sensor response for the samples deposited under different conditions. Finally the sample film deposited at 5 x 10-3 mbar, with applied power of 75 W in the presence of 8% oxygen, showed maximum sensitivity towards LPG.

碩士<br>國立交通大學<br>電機工程學系<br>102<br>This thesis aims to develop a system of mixture gas measurement which uses single gas sensor to detect varied harmful gas in sewer. Measure mixture gas in the environment; meanwhile, use difference voltage in the heater of front sensor in order to change sensor’s temperature. Then, use algorithm to distinguish mixture gas for achieving qualitative and quantitative. For the environment, the system uses single gas sensor which is used to detect varied mixture gas to complete all analysis. For the approach of changing sensor’s temperature, the thesis proposes two methods. First, when it has a reaction between sensor and gas, use two difference voltage in the heater separately to make the reaction steady both times. It is known as static state modulate. Second, when it has a reaction between sensor and gas, constantly vary voltage’s state and time in the heater to show a square wave of period. It is known as dynamic state modulate. The above-mentioned methods make that front sensor do not need to use multi-sensors to form array, single process do not need an additional algorithm to feature extraction and pattern recognition, and the application of system can be easier in single process in time domain. Besides viability of analysis method after measurement, also verify this method on MCU to achieve real time analysis and display purpose.

碩士<br>國立成功大學<br>化學工程學系<br>86<br>Multiple-layer indium oxide thin film with high surface area made up of a quasi-spherical grain have been prepared, base on rheotaxial growth andthermal oxidation(RGTO). Indium thin film, when growth, presence a surface characterized by spheroidal agglomerates due essentially to the surface tension of the liquid metal; these agglomerates do nto seen to have any tension of the liquid metal; these agglomerates do nto seen to have any electrical continuity. By means of thermal oxidation, both the transformation of the metal into a semiconductor and the thin filmcontinuity are obtained, owing to the volume increased during the above mentioned phase transformation. Using the same process, we got double-layeror triple-layer thin film.Alcohol electrical property measurements have been performed on samples withdifference multiple-layer in order to investigate the influence of surface area. The maximum sensitivity of triple- layer thin film towards 1850ppm of alcohol is equal to 3. The response times of single-layer film at 450 degreecentigrade is equal to 48 seccond, while the recovery times of triple- layerfilm at 500 degreee centigrade is equal to 282 second. At temperature higherthan 400 degree centigrade, these films have a higher sensistivity toward alcohol. The response kinetics of triple-layer film at 400 degree centigradeshowed the response is not smart.

碩士<br>大同大學<br>機械工程學系(所)<br>97<br>In the last decade, there are increasing investigations on lateral field excited (LFE) acoustic wave sensors in biochemical sensing applications due to their high sensitivity and simple fabrication. However, the research on this kind of sensor for gas detection is still awaited. Therefore, we adopted finite element method to analyze a LFE acoustic wave gas sensor, and further calculate its sensitivity to the variations of mass density and electrical conductivity of a selective film caused from gas concentration. In the meantime, quartz crystal microbalance (QCM) was also analyzed for comparison. Results show that the LFE sensor exhibits larger sensing range and higher sensitivity than the QCM. This is because no shielding electrode exists on sensing surface of the LFE sensor and hence the electric field can penetrate into the selective film. According to the simulation results,we conclude that a LFE acoustic wave sensor is very suitable to apply forgas detection.

碩士<br>大葉大學<br>機械工程研究所碩士班<br>94<br>ABSTRACT A novel micro formaldehyde gas sensor with a sputtered NiO thin film integrated with a micro hotplate was fabricated. A microfabricated formaldehyde gas sensor is developed which uses a silica substrate with Pt micro heaters as the micro hotplate and a thin-film NiO layer as a conductivity-sensitive material. The substrate is deposited with NiO thin film as sensing elements, Pt resistors as heaters, and as interdigitated electrodes for resistance measurement. As voltages were applied to Pt heaters, temperature of micro hotplates increased. Thus, at 300oC, when formaldehyde was present in the atmosphere, it was adsorbed and as a result the electrical conductivity of NiO films was increased. The measured resistance between the interdigitated electrodes was changed. The formaldehyde gas sensor was integrated with a Pt resistor as a micro heater for the enhancement of sensitivity. A high selectivity to acetone, methanol and ethanol was alson shown in the study.

碩士<br>國立中興大學<br>奈米科學研究所<br>103<br>In this research, we used spin coating method to make ZnO seed layer, and then growing massive high quality nanowires via aqueous solution method. After growth, we combined grew nanowires and self-make arrayed electrodes by dielectrophoresis method, and successfully produced room temperature CO sensing device. With the characterization of field-emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), grazing incidence X-ray diffraction (GIXRD), field emission transmission electron microscope (FE-TEM), and photoluminescence (PL), we knew that the grew nanowires were single crystalline and belongs to the wurtzite structure. As the growth time increasing from half hour to six hours, the average length would increase from 0.69 ± 0.03 μm to 2.40 ± 0.06 μm, and the average diameter would increase from 21.36 ± 0.48 nm to 96.17 ± 4.31 nm. After growing for two hours, the nanowire prefer to grow along [002], and the crystalline is best for growing for six hours. All the nanowires possess energy gap-emission at the wave length of about 378 ~ 383 nm. On the other hand, we fabricated a chip that contains 60 pairs of electrodes which the gap are about 2.28 μm, and put nanowires cross onto the electrodes to make sensing devices. From the I-V curve, we can know that the device are Schottky contact. And finally, we test the devices under room temperature and the alternating ambient between 10% CO and air. The best driving voltage were found as 2 V among 1 V to 3 V, and the average response and recovery time were about 48.37 and 65.61 seconds, and the response magnitude is about 6.8% at room temperature.