Dissertations / Theses on the topic 'Hotplate'

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.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.
Includes bibliographical references (p. 104-105).
This thesis characterizes a micro-hotplate designed at Draper Laboratory. This hotplate will be integrated into a calorimetry system that measures the heat released or absorbed by a reaction. An analytical thermal model is developed to quantify the heat transfer mechanisms between the hotplate and the environment. The analytical model is verified through experimental measurements conducted with the device operating in both ambient conditions and vacuum. In ambient conditions, the heat transfer is dominated by air conduction as predicted by the model. Air conduction can be reduced by operating the device in a medium with a lower thermal conductivity. The relatively short timescale over which the hotplate comes to thermal equilibrium with the environment limits the types of reactions that can be measured with the device. The performance of the hotplate can be improved by operating it in vacuum, by constructing it from a material with a lower emissivity, or by decreasing its surface area. The noise spectral density of the hotplate's resistive temperature sensor is characterized. The hotplate's ability to resolve temperature is limited by the flicker noise in the sensor.
by Radhika Baliga.
M.Eng.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2001.
Includes bibliographical references (p. 127-129).
Silicon carbide, high temperature, chemical sensors are the next step in chemical detection technology; allowing for the development of low cost, robust, lower power, and widely applicable chemical sensors. SiC offers the thermal conductivity, electrical properties, and operating temperatures not currently available in silicon sensors. Boston Micro Systems, a Wobum, Massachusetts based company, has developed technologies for bulk manufacturing of single crystal SiC material. Using this technology, geometries optimizing thermal and electrical performance have been developed to create a SiC micro-hotplate for chemical sensors. Under etching allows for the manufacturing of micro-hotplates. Micro hotplates allow sensors to discriminate between chemical species by controlling absorption and desorption of chemicals. Optimization of the performance of such a device is achieved by developing hotplates that are suspended by necked tethers. Tether designs minimize heat lose from the hotplate and necking creates heat generation regions. The excellent thermal properties of SiC allow heat to be transferred from the necked tethers to the hotplate; producing a hotplate with a uniform temperature distribution, important to the sensitivity and accuracy of the sensing film. Testing of tethered and necked hotplates identified several areas of improvement in hotplate design. These include under etching, improvement in the plates response to thermal stresses, and p-n junction performance improvements. Using such design improvements as tethers and necking the thermal performance of SiC micro-hotplates has improved by two orders of magnitude. This thesis discusses the design, modeling, and testing of single crystal SiC micro-hotplates.
Gregory Benn.
S.M.

There is great need for the widespread use of indoor gas monitors as modern hermetically-sealed domestic buildings increasingly suffer from indoor air pollution. However, neither modern technologies of gas sensors nor analytical instruments are ideally suited to this purpose. The problems of gas sensors are poor selectivity and the fact that normally they can detect only one gas, and analytical instruments suffer from their large size and high price. Therefore, the aim of the project is "to develop a novel gas sensor with low cost, low power consumption, high reliability, which can detect multiple gases with excellent selectivity" for indoor gas monitoring. In the first part of the project, an SOI-CMOS micro-hotplate with a single crystal silicon (SCS) resistive heater was proposed, fabricated and characterised. The design obviates issues of traditional heater materials i.e. platinum is not CMOS compatible and polysilicon is not thermally stable due to its polycrystalline structure. The SCS micro-hotplate was found to have an ultra low power consumption of 11.6 mW to operate at 500°C, and an excellent reliability with less than 1% drift after 500 hour operation at 500°C. In the second part, a novel temperature modulation technique for a carbon black/polymer composite sensor was theoretically derived based upon linear solvation and Fickian diffusion. The processing technique comprises only two steps; summing the off and on transient conductance signals from a temperature-stepped sensor, and subtracting the steady-state signal. The technique was demonstrated by applying to a carbon black/polyvinylpyrrolidone composite sensor employing the novel micro-hotplate. Identification of water. methanol and ethanol vapours was successfully demonstrated using the peak time of the resultant curve. Furthermore, quantification of those vapours was found to be possible using the height of the peaks, which was linearly proportional to the concentration. In conclusion, a novel low-cost gas sensor has been realised that is capable of detecting more than one gas with a single sensing element and thermal modulation. This has the potential for commercial exploitation in the area of indoor air pollution monitoring.

The subject of this thesis is focused on analysis of three test workplaces for final inspetion of a stove and determination of a workplace most appropriate for optimization. The thesis includes operating instructions of test equipment and test regulations of appliances that are tested on the production line. The analysis of the operation times was based on data measured in the MORA company and led to an idea of reducing the number of electric stoves positions and guaranteeing the same reliability of testing. The re-measurement of data and the comparison of results has been carried out.

Un dels majors problemes experimentats pels sistemes de detecció de gasos basats en sensors d'òxids metàl·lics és la seva manca de reproduibilitat, estabilitat i selectivitat. A fi i a efecte d'intentar resoldre aquest problemes, diferents estratègies han estat desenvolupades en paral·lel. Algunes es relacionen a la millora dels materials i d'altres impliquen el condicionament o el pre-tractament de les mostres. Les més emprades han consistit en aprofitar que els sensors presenten sensibilitats solapades per construir matrius de sensors i emprar tècniques de processament del senyal o bé utilitzar característiques de la resposta dinàmica dels sensors. En els darrers anys, modular la temperatura de treball del sensors d'òxids metàl·lics s'ha convertit en un dels mètodes més utilitzats per incrementar-ne la selectivitat. Això s'esdevé així donat que la resposta del sensor varia amb la seva temperatura de treball. Per això, en determinats casos, mesurant la resposta d'un sensor a n temperatures de treball diferents pot ser equivalent a tenir una matriu de n sensors diferents. Això permet obtenir informació multivariant de cada sensor individualment i ajuda a mantenir baixa la dimensionalitat del sistema de mesura per resoldre una determinada aplicació. Malgrat que molts i bons resultats han estat publicats dins aquest àmbit, la tria de les freqüències emprades en la modulació de la temperatura de treball dels sensor ha consistit fins ara en un procés empíric que no garanteix la obtenció dels millors resultats per una determinada aplicació. En aquest context, el principal objectiu d'aquesta tesi doctoral ha consistit en desenvolupar un mètode sistemàtic que permeti determinar quines són les freqüències de modulació òptimes que caldria emprar per resoldre un determinat problema d'anàlisi de gasos. Aquest mètode, extret del camp d'identificació de sistemes, ha esta desenvolupat i implementat per primer cop dins l'àmbit dels sensors de gasos. Aquest consisteix en estudiar la resposta dels sensors en presència de gasos mentre la temperatura de treball dels sensors és modulada per un senyal pseudo-aleatori de longitud màxima. Aquest senyals comparteixen algunes propietats amb el soroll blanc, i per tant poden ajudar a estimar la resposta lineal d'un sistema amb no-linealitats (per exemple, la resposta impulsional d'un sistema sensor-gas). El procés d'optimització es duu a terme mitjançant la selecció entre els components espectrals de les estimacions de la resposta impulsional, d'aquells que millor ajuden bé a discriminar o a quantificar els gasos objectiu dins una aplicació d'anàlisi de gasos donada. Tenint en compte que els components espectrals estan directament relacionats amb les xvii Improving the performance of micro-machined metal oxide gas sensors: Optimization of the temperature modulation mode via pseudo-random sequences. freqüències de modulació, la tria d'uns pocs components espectrals resulta en la determinació de les freqüències òptimes de modulació. En els primer experiments, senyals binaris pseudo-aleatoris van ser emprats per modular la temperatura de treball de sensors de gasos basats en òxids metàl·lics micro-mecanitzats dins d'un rang comprès entre 0 i 112,5 Hz. La freqüència superior és lleugerament superior a la frequència de tall de les membranes dels sensors. El resultat principal derivat d'aques estudi va ser que les freqüències de modulació interessants es trobaven en un rang comprès entre 0 i 1 Hz. Això és comprensible donat que la cinètica de les reaccions i dels processos d'adsorció que es produeixen en la superfície dels sensors són lentes i si aquestes s'han de veure modificades per la modulació térmica, llavors caldran senyals de modulació de baixa freqüència. Això explica perquè s'han vingut emprant senyals moduladores de temperatura en el rang dels mHz, malgrat que les membranes d'un dispositiu micromecanitzat presenten respostes tèrmiques molts més ràpides (típicament de l'ordre de 100 Hz). En els experiments que continuaren els primers, un mètode evolucionat per determinar les freqüències de modulació tèrmica òptimes va ser implementat. Aquest es basa en l'ús de seqüències pseudo-aleatòries multi-nivell de longitud màxima. Els senyals de tipus multi-nivell van ser considerats en substitució dels senyals binaris ja que els primers permeten obtenir una millor estimació que els segons de la dinàmica lineal d'un sistema amb no linealitats. I és ben conegut que els sensors de gasos basats en òxids metàl·lics presenten no linealitat en la seva resposta. Aquests estudis sistemàtics van ser completament validats mitjançant la síntesi de senyals multi-sinusoïdals amb les freqüències prèviament identificades emprant sequències pseudo-aleatòries. Quan la temperatura de treball dels sensors va ser modulada amb un senyal, el contingut freqüencial del qual era l'òptim, els gasos i les mescles de gasos considerades van poder ser discriminades perfectament i es va mostrar la possibilitat d'obtenir models de calibració acurats per predir la concentració dels gasos. En alguns casos, aquest procés de validació es va portar a terme emprant sensors que no havien estat utilitzats durant el procés d'optimització (per exemple, una agrupació de sensors diferent però del mateix lot de fabricació). En resum, el nou mètode desenvolupat en aquesta tesi per seleccionar les freqüències de modulació òptimes s'ha mostrat consistent i efectiu. El mètode és d'aplicació general i podria ser emprat en qualsevol problema d'anàlisi de gasos o bé estès a altres tipus de sensors (per exemple sensors polimèrics). Les contribucions científiques d'aquesta tesi s'han recollit en quatre articles en revistes internacionals i 13 llibres d'actes de conferències.
Uno de los mayores problemas experimentados en los sistemas de detección de gases basados en dispositivos de óxidos metálicos es su falta de reproducibilidad, estabilidad y selectividad. Con el fin de intentar resolver estos problemas, diferentes estrategias han sido desarrolladas en paralelo. Algunas de ellas se relacionan con la mejora de los materiales y otras implican acondicionamiento o pre-tratamiento de las muestras. Otras estrategias ampliamente empleadas consisten en aprovechar que los sensores presentan sensibilidades solapadas para construir matrices de sensores y emplear técnicas de procesamiento de señal o bien utilizar características de la respuesta dinámica de los sensores.En los últimos años, modular la temperatura de trabajo de los sensores de óxidos metálicos se ha convertido en uno de los métodos más utilizados para incrementar su selectividad. Esto se debe a, dado que la respuesta del sensor varía con su propia temperatura de trabajo, entonces, en determinados casos, midiendo la respuesta de un sensor a n temperaturas de trabajo diferentes, es equivalente a tener una matriz de n sensores diferentes. Esto permite obtener información multivariante de cada sensor individualmente y ayuda a mantener baja la dimensionalidad del sistema de medida para resolver una determinada aplicación. A pesar de los buenos resultados que han sido publicados dentro de este ámbito, la selección de las frecuencias empleadas en la modulación de la temperatura de trabajo de los sensores ha consistido, hasta el momento, en un proceso empírico lo que no garantiza la obtención de los mejores resultados para una determinada aplicación.En este contexto, el principal objetivo de esta tesis doctoral ha consistido en desarrollar un método sistemático que permita determinar cuales son las frecuencias de modulación óptimas que podrían emplearse para resolver un determinado problema de análisis de gases. Este método, extraído del campo de identificación de sistemas, ha sido desarrollado e implementado por primera vez dentro del ámbito de los sensores de gases. Éste consiste en estudiar la respuesta de los sensores en presencia de gases mientras la temperatura de trabajo de los sensores es modulada mediante una señal pseudo-aleatoria de longitud máxima. Estas señales comparten algunas propiedades con el ruido blanco, y por tanto pueden ayudar a estimar la respuesta lineal de un sistema con no-linealidades (por ejemplo, la respuesta impulsional de un sistema sensor-gas).El proceso de optimización es llevado a cabo mediante la selección entre las componentes espectrales de las estimaciones de la respuesta impulsional, de aquellas que más ayudan ya sea a discriminar o a cuantificar los gases objetivo dentro de una aplicación de análisis de gases dada. Teniendo en cuenta que las componentes espectrales están directamente relacionadas con las frecuencias de modulación, la selección de unas pocas componentes espectrales resulta en la determinación de las frecuencias optimas de modulación.En los primeres experimentos, señales binarias pseudo-aleatorias fueron utilizadas para modular la temperatura de trabajo de los sensores de gases basados en óxidos metálicos micro-mecanizados en un rango comprendido entre 0 a 112.5 Hz. La frecuencia superior es ligeramente mayor a la frecuencia de corte de las membranas de los sensores. El resultado principal derivado de estos estudios fue que las frecuencias de modulación interesantes se encuentran en un rango comprendido entre 0 y 1 Hz. Esto es comprensible dado que la cinética de las reacciones y de los procesos de adsorción que se producen en la superficie del sensor son lentos y si estos se han de alterar mediante la modulación térmica, se habrá de elaborar señales de modulación a bajas frecuencias. Esto explica por que se han venido empleado señales moduladoras de temperatura en el rango de los mHz, a pesar que las membranas de un dispositivo micro-mecanizado presentan respuestas mucho más rápidas (típicamente en el orden de los 100 Hz).En los experimentos posteriores a los primeros, un método evolucionado para determinar las frecuencias de modulación óptimas de los sensores micro-mecanizados fue implementado, el cual se basa en el uso de secuencias pseudo-aleatorias multi-nivel de longitud máxima (MLPRS). Las señales de tipo multi-nivel fueron consideradas en lugar de las binarias ya que las primeras permiten obtener una mejor estimación que las segundas de la dinámica lineal de un sistema con no linealidades. Y es bien conocido que los sensores de gases basados en óxidos metálicos presentan no-linealidades en su respuesta.Estos estudios sistemáticos fueron completamente validados mediante la síntesis de señales multi-senoidales con las frecuencias previamente identificadas utilizando secuencias pseudo-aleatorias. Cuando la temperatura de trabajo de los sensores fue modulada por una señal, el contenido frecuencial de la cual es el óptimo, los gases y mezclas de gases considerados pudieron ser discriminados perfectamente y se verificó la posibilidad de obtener modelos de calibración precisos para predecir la concentración de los gases. En algunos casos, estos procesos de validación se llevaron a cabo con sensores que no habían sido utilizados durante el proceso de optimización (por ejemplo, una agrupación de sensores diferentes pero del mismo lote de fabricación).En resumen, El nuevo método desarrollado in esta tesis para seleccionar las frecuencias de modulación optimas se a mostrado consistente y efectivo. El método es de aplicación general y podría ser utilizado en cualquier problema de análisis de gases o bien extendido a otro tipo de sensores (por ejemplo sensores poliméricos).Las contribuciones científicas de esta tesis se han recogido en 4 artículos en revistas internacionales y trece actas de conferencias.
One of the major problems in gas sensing systems that use metal oxide devices is the lack of reproducibility, stability and selectivity. In order to tackle these troubles experienced with metal oxide gas sensors, different strategies have been developed in parallel. Some of these are related to the improvement of materials, or the use of sample conditioning and pre-treating methods. Other widely used techniques include taking benefit of the unavoidable partially overlapping sensitivities by using sensor arrays and pattern recognition techniques or the use of dynamic features from the gas sensor response.In the last years, modulating the working temperature of metal oxide gas sensors has been one of the most used methods to enhance sensor selectivity. This occurs because, since, the sensor response is different at different working temperatures, and therefore, measuring the sensor response at n different temperatures is, in some cases, similar to the use of an array comprising n different sensors. This allows for measuring multivariate information from every single sensor and helps in keeping low the dimensionality of the measurement system needed to solve a specific application. Although the good results reported, until now, the selection of the frequencies used to modulate the working temperature remained an empirical process and that is not an accurate method to ensure that the best results are reached for a given application.In view of this context, the principal objective of this doctoral thesis was to develop a systematic method to determine which are the optimal temperature modulation frequencies to solve a given gas analysis problem. This method, which is borrowed from the field of system identification, has been developed and introduced for the first time in the area of gas sensors. It consists of studying the sensor response to gases when the operating temperature is modulated via maximum-length pseudo-random sequences. Such signals share some properties with white noise and, therefore, can be of help to estimate the linear response of a system with non-linearity (e.g., the impulse response of a sensor-gas system).The optimization process is conducted by selecting among the spectral components of the impulse response estimates, the few that better help either discriminating or quantifying the target gases of a given gas analysis application. Since spectral components are directly related to modulating frequencies, the selection of spectral components results in the determination of the optimal temperature modulating frequencies.In the first experiments, pseudo-random binary signals (PRBS) were employed to modulate the working temperature of micro-machined metal oxide gas sensors in a frequency range from 0 up to 112.5 Hz. The upper frequency is slightly higher than the cutoff frequency of the sensor membranes. The outcome of this initial study was that the important modulating frequencies were in the range between 0 and 1 Hz. This is understandable, since the kinetics of reaction and adsorption processes taking place at the sensor surface (i.e., physisorption/chemisorption/ionosorption) are slow and if these are to be altered by the thermal modulation, low frequency modulating signals need to be devised. This explains why low-frequency temperature-modulating signals (i.e. in the mHz range) have been used with micro-hotplate gas sensors, even though the thermal response of their membranes is much faster (typically, near 100 Hz).In the experiments that followed the first ones, an evolved method to determine the optimal temperature modulating frequencies for micro-hotplate gas sensors was introduced, which was based on the use of maximum length multilevel pseudo-random sequences (MLPRS). Multilevel signals were considered instead of the binary ones because the former can provide a better estimate than the latter of the linear dynamics of a process with non-linearity. And it is well known that temperature-modulated metal oxide gas sensors present non-linearity in their response.These systematic studies were fully validated by synthesizing multi-sinusoidal signals at the optimal frequencies previously identified using pseudo-random sequences. When the sensors had their operating temperatures modulated by a signal with a frequency content that corresponded to the optimal, the gases and gas mixtures considered could be perfectly discriminated and the building of accurate calibration models to predict gas concentration was found to be possible. In some cases, the validation process was conducted on sensors that had not been used for optimization purposes (e.g. a different sensor array from the same fabrication batch).Summarizing, the new method developed in this thesis for selecting the optimal modulating frequencies is shown to be consistent and effective. The method applies generally and could be used in any gas analysis problem or extended to other type of sensors (e.g. conducting polymer sensors).The scientific contributions of this thesis are collected in four journal papers and thirteen conference proceedings.

We studied the temperature transient behavior of an airpit-insulated micro hotplate (µHP) and aerogel-insulated µHP with different airpit heights and aerogel thicknesses. The µHP insulated by 1.3µm-thick aerogel consumes 26.7mW of power at 82°C with a time constant of 114.5 µsec, while the µHP insulated by 4?µm-thick aerogel consumes 35.6mW of power to provide 220°C with a time constant of 211.6 µsec. At the same time, a 100 µm-deep airpit-insulated ?HP consumes 18mW of power to reach approximately 400°C. The time constant of aerogel does not depend just on material properties but also on the structural design of the micro-heater. The temperature transient response time of µHPs is continued to improve from using air-pited, recessed silica aerogel, to thick-film silica aerogel.

This report collects selected outstanding scientific and technological results obtained within the frame of the European project "FLASiC" (Flash LAmp Supported Deposition of 3C-SiC) but also other work performed in adjacent fields. Goal of the project was the production of large-area epitaxial 3C-SiC layers grown on Si, where in an early stage of SiC deposition the SiC/Si interface is rigorously improved by energetic electromagnetic radiation from purpose-built flash lamp equipment developed at Forschungszentrum Rossendorf. Background of this work is the challenging task for areas like microelectronics, biotechnology, or biomedicine to meet the growing demands for high-quality electronic sensors to work at high temperatures and under extreme environmental conditions. First results in continuation of the project work – for example, the deposition of the topical semiconductor material zinc oxide (ZnO) on epitaxial 3C-SiC/Si layers – are reported too.

This report collects selected outstanding scientific and technological results obtained within the frame of the European project "FLASiC" (Flash LAmp Supported Deposition of 3C-SiC) but also other work performed in adjacent fields. Goal of the project was the production of large-area epitaxial 3C-SiC layers grown on Si, where in an early stage of SiC deposition the SiC/Si interface is rigorously improved by energetic electromagnetic radiation from purpose-built flash lamp equipment developed at Forschungszentrum Rossendorf. Background of this work is the challenging task for areas like microelectronics, biotechnology, or biomedicine to meet the growing demands for high-quality electronic sensors to work at high temperatures and under extreme environmental conditions. First results in continuation of the project work – for example, the deposition of the topical semiconductor material zinc oxide (ZnO) on epitaxial 3C-SiC/Si layers – are reported too.

碩士
國立臺北科技大學
製造科技研究所
99
This thesis presents the process of fully CMOS(complementary metal oxide semiconductor)-compatible with microhotplate, it apply gas-dry-etching on silicon substrate for anisotropic etching and intergrated on carbon monoxide(CO) sensor. Compare to the microhotplate and non-etching silicon substrate one, this microhotplate provided higher operating temperature under same ratio of power consumption, so the sensor could had higher temperature and cost lower power consumption while working. On the other hand, the 500 nm of tin oxide’s thin film (SnO2) of gas-sensing material were deposited successfully on the interdigited electrode by r.f. sputtering. Last, by different concentration of CO to measure its response characteristic, the result showed that in a short time period (150 sec), it had clear responding. This chip has been fabricated in industrial 0.35 μm CMOS technology and combined bulk micromachining of post-CMOS technologies to form the membrane –type device; this could prove that it could be applied on detecting of toxic gas.

碩士
國立交通大學
電控工程研究所
101
In this study, the design and fabrication of a micromachined LPD-based SnO2 gas sensor integrated with TaN micro-hotplate was carried out by utilizing MEMS technology. The advantage of TaN micro-heater is easy to design the geometrical shape. However, it could obtain many attractive characteristics, such as low power consumption, uniform thermal distribution, fast thermal response and high working temperature up to 700℃. In the design of the gas sensors, three different sensing film areas and, furthermore, three different edge length ratios of the membrane to micro-heater corresponding to each sensing film area are designed. In the characteristics of the micro-heater and sensing film, power consumption, thermal distribution, thermal response, gas sensing response and reliability were measured. Experimental results indicate that the optimum sensing film area and edge length ratios of the membrane to micro-heater are 100μm×100μm and 2.5, respectively, due to their low power consumption and high sensitivity. Besides, the experiment uses soaking on sensing surface to add copper to improve the selectivity and sensitivity of the sensors on hydrogen sulfide, and lower the working temperature and power consumption.

碩士
國立臺北科技大學
機電整合研究所
98
This thesis mainly describes the design rules of a micro hotplate (MHP) array which provides multiple-thermal distribution, and implementation of the MHP array by micro-electromechanical systems (MEMS) process. A micro-hotplate includes a micro-heater, a temperature sensor(s), a composite dielectric membrane and a thermoelectrical isolation layer. Typically geometrical designs of the micro-heater include meander, ring, square and interdigitated types. The temperature sensor detects resistance change and thermal coefficients via thermoresistive effect. The dielectric membrane layers are completed by KOH back etching process, which enables decreased thermal and electrical power losses. In this paper, ANSYS the finite element analysis (FEA) tool is employed to carry out simulations for design while feasible designs are initially considered. Electrothermal simulations are first performed for different geometries of micro-heaters, and it is found that the square heater superior to others can offer 540.16

Techn. Univ., Diss.--Ilmenau, 2003.
Parallel als Online-Ausg. erschienen unter der Adresse http://www.db-thueringen.de/servlets/DocumentServlet?id=1600. Im Rahmen dieser Arbeit wurde ein neuer SiC/HfB2-basierter Mikroheizer mit niedrigster Leistungsaufnahme für die Anwendung in Metalloxid-Gassensoren entwickelt und demonstriert. Erstmals wurden Siliziumkarbid (SiC) und Hafniumdiborid (HfB2) als Werkstoffe für einen Mikroheizer eingesetzt. Durch geringe Modifikation der Herstellungsprozesse lässt sich der Heizer so variieren, dass der Einsatz sowohl für den automobilen Anwendungsbereich (12V-24V) als auch für tragbare Geräte (1V-2V) für eine Vielzahl unterschiedlicher Messgase möglich ist. Es ist der erste Mikroheizer für Gassensoren überhaupt, der den Batteriebetrieb bei nur 1-2 V erlaubt. Der modulare Fertigungsansatz ermöglicht die Reduzierung der Entwicklungs- und Fertigungskosten für die unterschiedlichen Anwendungsbereiche. Aus der Marktentwicklung in der Sensorik, den industriellen Anforderungen und den zu den Metalloxid-Gassensoren im Wettbewerb stehenden alternativen Technologien ergeben sich das Anforderungsprofil des Sensors. Die Wahl der Materialien spielt eine Schlüsselrolle für die Heizereigenschaften. Der Mikroheizer besteht aus einer 1 (m dicken, an 150 (m langen und 10 bis 40 (m breiten Stegen aufgehängten Membran mit Außenmaßen von 100 (m x 100 (m. Alternativ kommen eine HfB2 - Dünnfilm-Widerstandsheizung oder ein dotierter SiC-Heizer zum Einsatz. Mit Leistungsaufnahmen von 32 mW werden Temperaturen von 600ʻC erreicht, was einer Effizienz von ca. 19 K/mW entspricht. Die verwendeten hexagonalen Strukturen ermöglichen dichtes Packen der Sensoren in Arrays bei hoher mechanischer Stabilität. Erste NO2 Sensoren mit gassensitiver In2O3 Schicht konnten gezeigt werden.

Micro-electro-mechanical systems (MEMS) became possible thanks to the silicon based technology used to fabricate integrated circuits. Originally, MEMS fabrication was limited to silicon based techniques and materials, but the expansion of MEMS applications brought the need of a wider catalog of materials, including polymers, now being used to fabricate MEMS. Polyimide is a very attractive polymer for MEMS fabrication due to its high temperature stability compared to other polymers, low coefficient of thermal expansion, low film stress and low cost. The goal of this thesis is to expand the Polyimide usage as structural material for MEMS by the development of a multi-user fabrication process for the integration of this polymer along with multiple metal layers on a silicon substrate. The process also integrates amorphous silicon as sacrificial layer to create free-standing structures. Dry etching is used to release the devices and avoid stiction phenomena. The developed process is used to fabricate platforms for micro-hotplate gas sensors. The fabrication steps for the platforms are described in detail, explaining the process specifics and capabilities. An initial testing of the micro-hotplate is presented. As the process was also used as educational tool, some designs made by students and fabricated with the Polyimide-MEMS process are also presented.

碩士
國立雲林科技大學
機械工程系
108
In this study, this work is mainly to design and fabricate the high sensitive low power consumption NO micro gas sensors with micro-hotplates. As we know that the semiconductor based gas sensors have many advantages such as high sensing response, small chip size, high device stability, low cost, high mass production capability, long lifetime and so on. However, a well micro-heater design is very important for gas sensor and will improve the performance and reliability of gas sensors significantly. Therefore, this study was mainly focused on the optimum design and fabrication of micro-hotplates set underneath the gas sensing film heating from below to improve the performance of NO gas sensors. In this thesis, the SnO2 metal oxide semiconductor was used as the NO gas sensing material and all the fabrication processes of the gas sensors needed were completed by using the IC and micro-electromechanical system (MEMS) processes. The work tasks of this study were included with (1) the design and simulation of micro-hotplates, (2) the design of structure and fabrication process of gas sensors, (3) the gas sensors fabrication, (4) the characterization of fabricated micro-hotplates, and (5) the characterization of fabricated NO gas sensors. In this result, the heating performance of the Ti heater/Al leads micro-hotplates are significantly better than the Ti heater/Ti leads micro-hotplates. The maximum temperatures of the Ti heater/Al leads micro-hotplates and the Ti heater/Ti leads micro-hotplates are 500 oC and 303 oC under an applied voltage of 4.5 V, respectively. In the optimal design, the responses of the Ti heater/Al leads micro-hotplate gas sensor are 65%, 73%, 80%, 88%, and 97% and the sensitivities of the Ti heater/Al leads micro-hotplate gas sensor are 1.129, 1.311, 1.487, 1.746 and 2.146, and the linearity is 96.6 %, respectively under the NO gas concentrations of 40 ppb, 80 ppb, 120 ppb, 160 ppb, 200 ppb at an operating temperature of 200 ℃.