A protocol for improving fabrication yield of thin SU-8 microcantilevers for use in an aptasensor

SU-8 negative photoresist has been extensively employed in the fabrication of microfluidics and microelectromechanical systems. This is due to its advantages including ease of fabrication using limited equipment, biocompatibility, excellent chemical resistance, and compatibility with silicon processing. In addition, its low Young’s modulus compared to silicon has made it an excellent choice for microcantilever structure development especially for sensing applications. This paper presents a fabrication protocol for the development of thin SU-8 microcantilevers. Factors such as baking temperatures and release methods that influence the fabrication yield of SU-8 microcantilevers are considered. The influence of the baking temperature on the deformation of the SU-8 structure is investigated using the finite element method and verified experimentally. Three release methods are studied including a dry release method using fluorocarbon film, and two wet release methods using OmniCoat sacrificial layer and polymethyl methacrylate (PMMA) sacrificial layer. The wet release method using PMMA sacrificial layer produced the highest yield. An aptasensor is formed using the SU-8 microcantilever, and its deflection measured for thrombin detection.

Electromechanical properties of calcium bismuth titanate films: A potential candidate for lead-free thin-film piezoelectrics

CaBi4Ti4O15 (CBTi144) thin films were evaluated for use as lead-free thin-film piezoelectrics in microelectromechanical systems. The films were grown by the polymeric precursor method on (100)Pt/Ti/SiO2/Si substrates. The a/b-axis orientation of the ferroelectric film is considered to be associated with the preferred orientation of the Pt bottom electrode. The P-r and E-c were 14 mu C/cm(2) and 64 kV/cm, respectively, for a maximum applied field of 400 kV/cm. The domain structure was investigated by piezoresponse force microscopy. The film has a piezoelectric coefficient, d(33), equal to 60 pm/V and a current density of 0.7 mA/cm(2).

Optimal linear control to parametric uncertainties in a micro electro mechanical system

This paper, a micro-electro-mechanical systems (MEMS) with parametric uncertainties is considered. The non-linear dynamics in MEMS system is demonstrated with a chaotic behavior. We present the linear optimal control technique for reducing the chaotic movement of the micro-electromechanical system with parametric uncertainties to a small periodic orbit. The simulation results show the identification by linear optimal control is very effective. © 2013 Academic Publications, Ltd.

Effects of railway track vibration induced by passing trains on an energy harvesting device

Pós-graduação em Engenharia Mecânica - FEIS

Evaluation der Langzeitcompliance lebertransplantierter Patienten mit der immunsuppressiven Therapie und eines Betreuungsmodells zur intersektoralen kooperativen pharmazeutischen Betreuung durch eine Krankenhausapotheke und öffentliche Apotheken

Ein wichtiger Baustein für den langfristigen Erfolg einer Lebertransplantation ist die Compliance mit der lebenslang einzunehmenden immunsuppressiven Therapie. Im Rahmen der vorliegenden Arbeit wurde erstmals mittels MEMS® die Compliance bei lebertransplantierten Patienten untersucht, deren Transplantation einige Jahre zurücklag. Rekrutiert wurden Patienten, die vor 2, 5, 7 oder 10 Jahren (Gruppe 2 y.p.t., 5 y.p.t., 7 y.p.t., 10 y.p.t.) in der Universitätsmedizin Mainz lebertransplantiert wurden. 39 Patienten nahmen an der prospektiven Anwendungsbeobachtung teil. Die Compliance wurde mittels MEMS® über eine Beobachtungszeit von 6 Monaten erfasst. Bei der MEMS®-Auswertung war zu vermuten, dass 10 Patienten diese nicht wie vorgesehen verwendet hatten. Folglich konnten die mittels MEMS® gemessenen Compliance-Parameter nur für 29 Patienten valide ermittelt werden. Die mittlere Dosing Compliance betrug 81 ± 21 %, wobei die Gruppe 2 y.p.t. mit 86 ± 14 % bessere Werte zu verzeichnen hatte als die Gruppe 5 y.p.t. (75 ± 27 %) und 7 y.p.t. (74 ± 28 %). Die Ergebnisse waren jedoch nicht signifikant unterschiedlich (p=0,335, Kruskal-Wallis-Test). Unter Einbeziehung aller mittels MEMS® gemessenen Compliance-Parameter wurden 19 von 29 Patienten (66 %) als compliant eingestuft. Bei der Analyse der Gesamtcompliance basierend auf den subjektiven Compliance-Messmethoden (Morisky-Fragebogen, MESI-Fragebogen, Selbsteinschätzung), der Arzneimittel-Blutspiegel und der Anzahl an Abstoßungsreaktionen, in der alle 39 Patienten einbezogen werden konnten, wurden 35 Patienten (90 %) als compliant eingestuft. rnIm zweiten Teil der Arbeit wurde die Etablierung und Bewertung eines intersektoralen Pharmazeutischen Betreuungskonzepts für lebertransplantierte Patienten untersucht. Erstmals wurden anhand eines entwickelten schnittstellenübergreifenden, integrierten Betreuungskonzepts niedergelassene Apotheker in die Pharmazeutische Betreuung lebertransplantierter Patienten eingebunden. 20 Patienten wurden rekrutiert und während ihres stationären Aufenthaltes nach Transplantation pharmazeutisch betreut. Die Betreuung umfasste eine intensive Patientenschulung mit drei bis vier Gesprächen durch einen Krankenhausapotheker. Während des stationären Aufenthaltes wurden arzneimittelbezogene Probleme erkannt, gelöst und dokumentiert. Bei Entlassung stellte der Krankenhausapotheker einen Medikationsplan für den Hausarzt sowie für den niedergelassenen Apotheker aus und führte mit den Patienten ein ausführliches Entlassungsgespräch. Darüber hinaus wurden den Patienten Arzneimitteleinnahmepläne und eine Patienteninformation über ihr immunsuppressives Arzneimittel übergeben. 15 Patienten konnten daraufhin ambulant von niedergelassenen Apothekern pharmazeutisch weiterbetreut werden. Das kooperierende pharmazeutische Personal wurde durch ein eigens für die Studie erstelltes Manual zur Pharmazeutischen Betreuung lebertransplantierter Patienten geschult und unterstützt. Die niedergelassenen Apotheker sollten die Patienten in ihrer Arzneimitteltherapie begleiten, indem Beratungsgespräche geführt und arzneimittelbezogene Probleme erkannt und gelöst wurden. Die Nutzeffekte der intensiven Pharmazeutischen Betreuung konnte anhand verschiedener Erhebungsinstrumente dargelegt werden. Im Ergebnis resultierte eine hohe Zufriedenheit der Patienten und Apotheker mit dem Betreuungskonzept, die mittels Selbstbeurteilungsfragebögen ermittelt wurde. Die Compliance der Patienten wurde anhand des Morisky- und MESI-Fragebogens, der Selbsteinschätzung der Patienten, Blutspiegelbestimmungen sowie der Einschätzung durch den niedergelassenen Apotheker bestimmt. 86 % der Patienten wurden als compliant eingeordnet. Die Kenntnisse der Patienten über ihre immunsuppressive Therapie, welche anhand von Interviews erfragt wurden, lagen auf einem sehr hohen Niveau. Abschließend kann festgestellt werden, dass die Pharmazeutische Betreuung lebertransplantierter Patienten in den niedergelassenen Apotheken durchführbar ist. Anhand der Dokumentationsprotokolle lässt sich allerdings nur sehr schwer beurteilen, in welchem Maße die Betreuung tatsächlich erfolgte. Das tatsächliche vorliegen einer mangelnden Betreuung oder aber eine lückenhafte Dokumentation der Betreuungsleistung war nicht zu differenzieren. Ein limitierender Faktor für die intensivierte Betreuung ist sicherlich der erhebliche Aufwand für nur einen Patienten mit einem seltenen Krankheitsbild. Das Erkennen und Lösen von 48 ABP durch den Krankenhausapotheker und 32 ABP durch die niedergelassenen Apotheker, d. h. insgesamt 4,5 ABP pro Patient zeigt, dass die Pharmazeutische Betreuung einen wichtigen Beitrag für eine qualitätsgesicherte Arzneimitteltherapie leistet. Die intersektorale Pharmazeutische Betreuung stellt eine wesentliche Hilfe und Unterstützung der Patienten im sicheren Umgang mit ihrer Arzneimitteltherapie dar.rn

Development and characterization of micromachined devices for separation techniques

Nowadays microfluidic is becoming an important technology in many chemical and biological processes and analysis applications. The potential to replace large-scale conventional laboratory instrumentation with miniaturized and self-contained systems, (called lab-on-a-chip (LOC) or point-of-care-testing (POCT)), offers a variety of advantages such as low reagent consumption, faster analysis speeds, and the capability of operating in a massively parallel scale in order to achieve high-throughput. Micro-electro-mechanical-systems (MEMS) technologies enable both the fabrication of miniaturized system and the possibility of developing compact and portable systems. The work described in this dissertation is towards the development of micromachined separation devices for both high-speed gas chromatography (HSGC) and gravitational field-flow fractionation (GrFFF) using MEMS technologies. Concerning the HSGC, a complete platform of three MEMS-based GC core components (injector, separation column and detector) is designed, fabricated and characterized. The microinjector consists of a set of pneumatically driven microvalves, based on a polymeric actuating membrane. Experimental results demonstrate that the microinjector is able to guarantee low dead volumes, fast actuation time, a wide operating temperature range and high chemical inertness. The microcolumn consists of an all-silicon microcolumn having a nearly circular cross-section channel. The extensive characterization has produced separation performances very close to the theoretical ideal expectations. A thermal conductivity detector (TCD) is chosen as most proper detector to be miniaturized since the volume reduction of the detector chamber results in increased mass and reduced dead volumes. The microTDC shows a good sensitivity and a very wide dynamic range. Finally a feasibility study for miniaturizing a channel suited for GrFFF is performed. The proposed GrFFF microchannel is at early stage of development, but represents a first step for the realization of a highly portable and potentially low-cost POCT device for biomedical applications.

Compliance lebertransplantierter Patienten mit dem Immunsuppressivum Tacrolimus bei 2x täglicher im Vergleich zu 1x täglicher Einnahme

Compliance lebertransplantierter Patienten mit der immunsuppressiven Therapie ist unerlässlich für den lang-fristigen Erfolg der Lebertransplantation. Aus Non-Compliance mit der immunsuppressiven Therapie können Abstoßungsreaktionen, Organverlust oder sogar Tod resultieren. Hauptziel der vorliegenden Studie war die erstmalige Evaluation der Compliance bei Einnahme von Prograf® (zweimal tägliche Einnahme von Tacrolimus) im Vergleich zur Einnahme von Advagraf® (einmal tägliche Einnahme von Tacrolimus). Von Interesse war außerdem die Fragestellung, ob sich die Compliance bezüglich der immunsuppressiven Therapie mit dem Zeitabstand zur Transplantation verändert. rnDie Compliancemessung wurde offen mittels MEMS® (Aardex Ltd., Schweiz) durchgeführt, der Patient war also über die Compliancekontrolle informiert. Mittels MEMS® konnten Datum und Uhrzeit der Dosisentnahme dokumentiert und damit zuverlässig das gesamte Compliancemuster über im Durchschnitt 176 Tage mit der zweimal täglichen Einnahme und 188 Tage mit der einmal täglichen Einnahme pro Patient erfasst werden. 65 Patienten mit dem Basisimmunsuppressivum Prograf® wurden in die prospektive, nicht-interventionelle Studie eingeschlossen und nach Per Protokoll-Analyse konnten die Daten von 63 in Mainz lebertransplantierten Patienten ausgewertet werden (Prograf®: Gruppe 1: 15 Patienten (Pat.), Gruppe 2: 23 Pat., Gruppe 3: 22 Pat., Drop-outs: 3 Pat.; Advagraf®: Gruppe 1: 16 Pat., Gruppe 2: 23 Pat., Gruppe 3: 23 Pat., Drop-outs: 1 Pat.). Die Dosing Compliance (DC), definiert als Prozent der Tage, an denen der MEMS®-Behälter korrekt geöffnet und die Dosis höchstwahrscheinlich korrekt eingenommen wurde, war der primäre Zielparameter. Weitere Methoden der Compliancemessung, wie der Pill Count, mehrere Fragebögen (Selbsteinschätzung, Patientenwissen-, Morisky-, MESI-, HADS-, SF-36- und Patientenzufriedenheit-Fragebogen) sowie die Blutspiegelmessung wurden eingesetzt, um die Compliance der Patienten umfassend charakterisieren zu können. rnDer Median der DC mit der zweimal täglichen Einnahme betrug 97% bei Pat. > 6 m.p.t. < 2 y.p.t., 97% bei Pat. > 2 y.p.t. < 5 y.p.t. und 98% bei Pat. > 5 y.p.t. (p=0,931; Kruskal-Wallis-Test). Der Median der DC von Tacroli-mus bei einmal täglicher Einnahme (Advagraf®) betrug 99% bei Pat. > 6 m.p.t. < 2 y.p.t., 98% bei Pat. > 2 y.p.t. < 5 y.p.t. und 97% bei Pat. > 5 y.p.t. (p=0,158; Kruskal-Wallis-Test). Insgesamt zeigten die Patienten während des gesamten Beobachtungszeitraums von 12 Monaten eine gute Compliance für die Einnahme ihres Immun-suppressivums. Die Timing Compliance (TiC)-raten lagen auf einem niedrigeren Niveau als die Dosing- und Taking Compliance (TC)-raten. Die Complianceraten der drei Subgruppen unterschieden sich nicht signifikant. Die Patienten mit dem geringsten Abstand zur Transplantation zeigten bei beinahe allen Messmethoden die höchste Compliance im Gegensatz zur etwas geringeren Compliance der Patienten mit größerem Abstand zur Transplantation. Die während der Advagraf®-Phase mittels MEMS® gemessenen DC-, TC- und TiC-raten fielen höher aus als bei Einnahme von Prograf® (p(DC)=0,003; p(TC)=0,077; p(TiC)=0,003; Wilcoxon Vorzeichen-Rang-Test). Dieses Ergebnis untermauert die in anderen Indikationen gefundene Complianceverbesserung durch die einmal tägliche Arzneimittelgabe im Vergleich zur zweimal täglichen Gabe. Die Auswertung der Drug Holidays ergab für die Advagraf®-Phase hingegen niedrigere Complianceraten als für die Prograf®-Phase. Dieses Ergebnis ist auf die Definition des Drug Holidays (keine Arzneimitteleinnahme über 48 h) zurück zu führen. Die Chance Advagraf® einmal pro Tag zu vergessen ist doppelt so hoch, als Prograf® dreimal aufeinander fol-gend zu vergessen. Mit einer verhältnismäßigeren Definition von Drug Holidays (Einnahmepause von 72 Stun-den bei einmal täglicher Einnahme von Advagraf® entsprechend drei ausgelassenen Dosen von Prograf®) ist die Compliancerate 81%. Die Ergebnisse des Pill Counts waren sowohl bei Einnahme von Prograf® als auch von Advagraf® mit der jeweils gemessenen TC vergleichbar, was die Zuverlässigkeit der Messergebnisse bes-tätigt. rnDie zusätzlich eingesetzten Methoden verifizierten das Ergebnis der höheren Compliance mit der einmal tägli-chen Einnahme. Die während der Advagraf®-Phase beantworteten Fragebögen zeigten einen Trend zu besserer Compliance und Lebensqualität. Lediglich die Ergebnisse des MESI-Fragebogens und der Blutspiegelmessungen wichen sowohl während der Prograf®- als auch während der Advagraf®-Phase stark von den Ergebnis-sen der anderen Methoden ab. rnUnter Einbeziehung aller mittels MEMS® und Pill Count objektiv gemessenen Complianceparameter konnten während der Prograf®-Einnahme 54 von 60 Pat. (90%) und während der Advagraf®-Phase 59 von 62 Pat. (95%) als compliant eingestuft werden. Aufgrund subjektiver Compliancemessungen waren 49 von 58 Pat. (84%) während der Prograf®- und 54 von 59 Pat. (92%) während der Advagraf®-Phase als compliant einzustufen. Es wurde beobachtet, dass die zeitlich korrekte Einnahme der Morgendosis einfacher und bei Einmalgabe zu bevorzugen ist. Die wochentagsbezogene Auswertung ergab erwartungsgemäß, dass am Wochenende (Samstag und Sonntag) am häufigsten Dosen ausgelassen wurden. rnDie Umstellung von Prograf® auf Advagraf® stellte kein Problem dar. Beinahe alle Patienten waren dankbar und zufrieden mit der Reduzierung der Dosierungsfrequenz und der größeren Unabhängigkeit durch die entfallene abendliche Einnahme. Der positive Einfluss der geringeren Dosierungshäufigkeit auf die Langzeitcompliance der Patienten, ist ein hinreichender Grund die Entwicklung von Formulierungen zur einmal täglichen Ein-nahme für weitere Immunsuppressiva zu fordern. Insbesondere bei den häufig eingesetzten Kombinationstherapien von Immunsuppressiva würde der Effekt der Complianceverbesserung noch verstärkt werden, wenn alle eingesetzten Immunsuppressiva zur einmal täglichen Gabe geeignet wären.

Localized annealing of polysilicon microstructures by inductively heated ferromagnetic films

The monolithic integration of dissimilar microsystems is often limited by conflicts in thermal budget. One of the most prevalent examples is the fabrication of active micro-electromechanical systems (MEMS), as structural films utilized for surface micromachining such as polysilicon typically require processing at temperatures unsuitable for microelectronic circuitry. A localized annealing process could provide for the post-deposition heat treatment of integrated structures without compromising active devices. This dissertation presents a new microfabrication technology based on the inductive heating of ferromagnetic films patterned to define regions for heat treatment. Support is provided through theory, finite-element modeling, and experimentation, concluding with the demonstration of inductive annealing on polysilicon inertial sensing structures. Though still in its infancy, the results confirm the technology to be a viable option for integrated MEMS as well as any microsystem fabrication process requiring a thermal gradient.

Laser Shock Microformingof Thin Metal Sheets with ns Lasers

Continuous and long-pulse lasers have been used for the forming of metal sheets in macroscopic mechanical applications. However, for the manufacturing of micro-electromechanical systems (MEMS), the use of ns laser pulses provides a suitable parameter matching over an important range of sheet components that, preserving the short interaction time scale required for the predominantly mechanical (shock) induction of deformation residual stresses, allows for the successful processing of components in a medium range of miniaturization without appreciable thermal deformation.. In the present paper, the physics of laser shock microforming and the influence of the different experimental parameters on the net bending angle are presented.

Design, Technology and Characterization of Micromechanised Sensors and Actuators for Harsh Environments

Los sistemas micro electro mecánicos (MEMS) han demostrado ser una exitosa familia de dispositivos que pueden usarse como plataforma para el desarrollo de dispositivos con aplicaciones en óptica, comunicaciones, procesado de señal y sensorización. Los dispositivos MEMS estándar suelen estar fabricados usando tecnología de silicio. Sin embargo, el rendimiento de estos MEMS se puede mejorar si se usan otros materiales. Por ejemplo, el diamante nanocristalino (NCD) ofrece unas excelentes propiedades mecánicas, transparencia y una superficie fácil de funcionalizar. Por otro lado, el sistema de materiales (In; Ga; Al)N, los materiales IIIN, se pueden usar para producir estructuras monocristalinas con alta sensibilidad mecánica y química. Además, el AlN se puede depositar por pulverización catódica reactiva sobre varios substratos, incluyendo NCD, para formar capas policristalinas orientadas con alta respuesta piezoeléctrica. Adicionalmente, tanto el NCD como los materiales III-N muestran una gran estabilidad térmica y química, lo que los hace una elección idónea para desarrollar dispositivos para aplicaciones para alta temperatura, ambientes agresivos e incluso para aplicaciones biocompatibles. En esta tesis se han usado estos materiales para el diseño y medición de demostradores tecnológicos. Se han perseguido tres objetivos principales: _ Desarrollo de unos procesos de fabricación apropiados. _ Medición de las propiedades mecánicas de los materiales y de los factores que limitan el rendimiento de los dispositivos. _ Usar los datos medidos para desarrollar dispositivos demostradores complejos. En la primera parte de esta tesis se han estudiado varias técnicas de fabricación. La estabilidad de estos materiales impide el ataque y dificulta la producción de estructuras suspendidas. Los primeros capítulos de esta disertación se dedican al desarrollo de unos procesos de transferencia de patrones por ataque seco y a la optimización del ataque húmedo sacrificial de varios substratos propuestos. Los resultados de los procedimientos de ataque se presentan y se describe la optimización de las técnicas para la fabricación de estructuras suspendidas de NCD y materiales III-N. En un capítulo posterior se estudia el crecimiento de AlN por pulverización catódica. Como se ha calculado en esta disertación para obtener una actuación eficiente de MEMS, las capas de AlN han de ser finas, típicamente d < 200 nm, lo que supone serias dificultades para la obtención de capas orientadas con respuesta piezoeléctrica. Las condiciones de depósito se han mapeado para identificar las fronteras que proporcionan el crecimiento de material orientado desde los primeros pasos del proceso. Además, durante la optimización de los procesos de ataque se estudió un procedimiento para fabricar películas de GaN nanoporoso. Estas capas porosas pueden servir como capas sacrificiales para la fabricación de estructuras suspendidas de GaN con baja tensión residual o como capas para mejorar la funcionalización superficial de sensores químicos o biológicos. El proceso de inducción de poros se discutirá y también se presentarán experimentos de ataque y funcionalización. En segundo lugar, se han determinado las propiedades mecánicas del NCD y de los materiales III-N. Se han fabricado varias estructuras suspendidas para la medición del módulo de Young y de la tensión residual. Además, las estructuras de NCD se midieron en resonancia para calcular el rendimiento de los dispositivos en términos de frecuencia y factor de calidad. Se identificaron los factores intrínsecos y extrínsecos que limitan ambas figuras de mérito y se han desarrollado modelos para considerar estas imperfecciones en las etapas de diseño de los dispositivos. Por otra parte, los materiales III-N normalmente presentan grandes gradientes de deformación residual que causan la deformación de las estructuras al ser liberadas. Se han medido y modelado estos efectos para los tres materiales binarios del sistema para proporcionar puntos de interpolación que permitan predecir las características de las aleaciones del sistema III-N. Por último, los datos recabados se han usado para desarrollar modelos analíticos y numéricos para el diseño de varios dispositivos. Se han estudiado las propiedades de transducción y se proporcionan topologías optimizadas. En el último capítulo de esta disertación se presentan diseños optimizados de los siguientes dispositivos: _ Traviesas y voladizos de AlN=NCD con actuación piezoeléctrica aplicados a nanoconmutadores de RF para señales de alta potencia. _ Membranas circulares de AlN=NCD con actuación piezoeléctrica aplicadas a lentes sintonizables. _ Filtros ópticos Fabry-Pérot basados en cavidades aéreas y membranas de GaN actuadas electrostáticamente. En resumen, se han desarrollado unos nuevos procedimientos optimizados para la fabricación de estructuras de NCD y materiales III-N. Estas técnicas se han usado para producir estructuras que llevaron a la determinación de las principales propiedades mecánicas y de los parámetros de los dispositivos necesarios para el diseño de MEMS. Finalmente, los datos obtenidos se han usado para el diseño optimizado de varios dispositivos demostradores. ABSTRACT Micro Electro Mechanical Systems (MEMS) have proven to be a successful family of devices that can be used as a platform for the development of devices with applications in optics, communications, signal processing and sensorics. Standard MEMS devices are usually fabricated using silicon based materials. However, the performance of these MEMS can be improved if other material systems are used. For instance, nanocrystalline diamond (NCD) offers excellent mechanical properties, optical transparency and ease of surface functionalization. On the other hand, the (In; Ga; Al)N material system, the III-N materials, can be used to produce single crystal structures with high mechanical and chemical sensitivity. Also, AlN can be deposited by reactive sputtering on various substrates, including NCD, to form oriented polycrystalline layers with high piezoelectric response. In addition, both NCD and III-N materials exhibit high thermal and chemical stability, which makes these material the perfect choice for the development of devices for high temperatures, harsh environments and even biocompatible applications. In this thesis these materials have been used for the design and measurement of technological demonstrators. Three main objectives have been pursued: _ Development of suitable fabrication processes. _ Measurement of the material mechanical properties and device performance limiting factors. _ Use the gathered data to design complex demonstrator devices. In a first part of the thesis several fabrication processes have been addressed. The stability of these materials hinders the etching of the layers and hampers the production of free standing structures. The first chapters of this dissertation are devoted to the development of a dry patterning etching process and to sacrificial etching optimization of several proposed substrates. The results of the etching processes are presented and the optimization of the technique for the manufacturing of NCD and III-N free standing structures is described. In a later chapter, sputtering growth of thin AlN layers is studied. As calculated in this dissertation, for efficient MEMS piezoelectric actuation the AlN layers have to be very thin, typically d < 200 nm, which poses serious difficulties to the production of c-axis oriented material with piezoelectric response. The deposition conditions have been mapped in order to identify the boundaries that give rise to the growth of c-axis oriented material from the first deposition stages. Additionally, during the etching optimization a procedure for fabricating nanoporous GaN layers was also studied. Such porous layers can serve as a sacrificial layer for the release of low stressed GaN devices or as a functionalization enhancement layer for chemical and biological sensors. The pore induction process will be discussed and etching and functionalization trials are presented. Secondly, the mechanical properties of NCD and III-N materials have been determined. Several free standing structures were fabricated for the measurement of the material Young’s modulus and residual stress. In addition, NCD structures were measured under resonance in order to calculate the device performance in terms of frequency and quality factor. Intrinsic and extrinsic limiting factors for both figures were identified and models have been developed in order to take into account these imperfections in the device design stages. On the other hand, III-N materials usually present large strain gradients that lead to device deformation after release. These effects have been measured and modeled for the three binary materials of the system in order to provide the interpolation points for predicting the behavior of the III-N alloys. Finally, the gathered data has been used for developing analytic and numeric models for the design of various devices. The transduction properties are studied and optimized topologies are provided. Optimized design of the following devices is presented at the last chapter of this dissertation: _ AlN=NCD piezoelectrically actuated beams applied to RF nanoswitches for large power signals. _ AlN=NCD piezoelectrically actuated circular membranes applied to tunable lenses. _ GaN based air gap tunable optical Fabry-Pérot filters with electrostatic actuation. On the whole, new optimized fabrication processes has been developed for the fabrication of NCD and III-N MEMS structures. These processing techniques was used to produce structures that led to the determination of the main mechanical properties and device parameters needed for MEMS design. Lastly, the gathered data was used for the design of various optimized demonstrator devices.

Localized heating or cooling in mesoscopic devices by electron transport

We describe a method to produce local heating or cooling (depending on how the system is tuned) in a mesoscopic device by transport of electrons. The mechanism can operate on molecules or quantum dots, or any system where the local modes are coupled to vibrations. We believe this will be of future interest in micro electro mechanical systems (MEMS). The amount of heating/cooling obtained depends on the details of the device. We also perform a numerical calculation to display the effect. (C) 2004 Elsevier B.V. All rights reserved.

Lattice Boltzmann method for flow and heat transfer in microgeometries

Recent technological developments have made it possible to design various microdevices where fluid flow and heat transfer are involved. For the proper design of such systems, the governing physics needs to be investigated. Due to the difficulty to study complex geometries in micro scales using experimental techniques, computational tools are developed to analyze and simulate flow and heat transfer in microgeometries. However, conventional numerical methods using the Navier-Stokes equations fail to predict some aspects of microflows such as nonlinear pressure distribution, increase mass flow rate, slip flow and temperature jump at the solid boundaries. This necessitates the development of new computational methods which depend on the kinetic theory that are both accurate and computationally efficient. In this study, lattice Boltzmann method (LBM) was used to investigate the flow and heat transfer in micro sized geometries. The LBM depends on the Boltzmann equation which is valid in the whole rarefaction regime that can be observed in micro flows. Results were obtained for isothermal channel flows at Knudsen numbers higher than 0.01 at different pressure ratios. LBM solutions for micro-Couette and micro-Poiseuille flow were found to be in good agreement with the analytical solutions valid in the slip flow regime (0.01 < Kn < 0.1) and direct simulation Monte Carlo solutions that are valid in the transition regime (0.1 < Kn < 10) for pressure distribution and velocity field. The isothermal LBM was further extended to simulate flows including heat transfer. The method was first validated for continuum channel flows with and without constrictions by comparing the thermal LBM results against accurate solutions obtained from analytical equations and finite element method. Finally, the capability of thermal LBM was improved by adding the effect of rarefaction and the method was used to analyze the behavior of gas flow in microchannels. The major finding of this research is that, the newly developed particle-based method described here can be used as an alternative numerical tool in order to study non-continuum effects observed in micro-electro-mechanical-systems (MEMS).

Lattice Boltzmann Method for Flow and Heat Transfer in Microgeometries

Recent technological developments have made it possible to design various microdevices where fluid flow and heat transfer are involved. For the proper design of such systems, the governing physics needs to be investigated. Due to the difficulty to study complex geometries in micro scales using experimental techniques, computational tools are developed to analyze and simulate flow and heat transfer in microgeometries. However, conventional numerical methods using the Navier-Stokes equations fail to predict some aspects of microflows such as nonlinear pressure distribution, increase mass flow rate, slip flow and temperature jump at the solid boundaries. This necessitates the development of new computational methods which depend on the kinetic theory that are both accurate and computationally efficient. In this study, lattice Boltzmann method (LBM) was used to investigate the flow and heat transfer in micro sized geometries. The LBM depends on the Boltzmann equation which is valid in the whole rarefaction regime that can be observed in micro flows. Results were obtained for isothermal channel flows at Knudsen numbers higher than 0.01 at different pressure ratios. LBM solutions for micro-Couette and micro-Poiseuille flow were found to be in good agreement with the analytical solutions valid in the slip flow regime (0.01 < Kn < 0.1) and direct simulation Monte Carlo solutions that are valid in the transition regime (0.1 < Kn < 10) for pressure distribution and velocity field. The isothermal LBM was further extended to simulate flows including heat transfer. The method was first validated for continuum channel flows with and without constrictions by comparing the thermal LBM results against accurate solutions obtained from analytical equations and finite element method. Finally, the capability of thermal LBM was improved by adding the effect of rarefaction and the method was used to analyze the behavior of gas flow in microchannels. The major finding of this research is that, the newly developed particle-based method described here can be used as an alternative numerical tool in order to study non-continuum effects observed in micro-electro-mechanical-systems (MEMS).

Design, Fabrication, and Characterization of Carbon Nanotube Field Emission Devices for Advanced Applications

Carbon nanotubes (CNTs) have recently emerged as promising candidates for electron field emission (FE) cathodes in integrated FE devices. These nanostructured carbon materials possess exceptional properties and their synthesis can be thoroughly controlled. Their integration into advanced electronic devices, including not only FE cathodes, but sensors, energy storage devices, and circuit components, has seen rapid growth in recent years. The results of the studies presented here demonstrate that the CNT field emitter is an excellent candidate for next generation vacuum microelectronics and related electron emission devices in several advanced applications.

The work presented in this study addresses determining factors that currently confine the performance and application of CNT-FE devices. Characterization studies and improvements to the FE properties of CNTs, along with Micro-Electro-Mechanical Systems (MEMS) design and fabrication, were utilized in achieving these goals. Important performance limiting parameters, including emitter lifetime and failure from poor substrate adhesion, are examined. The compatibility and integration of CNT emitters with the governing MEMS substrate (i.e., polycrystalline silicon), and its impact on these performance limiting parameters, are reported. CNT growth mechanisms and kinetics were investigated and compared to silicon (100) to improve the design of CNT emitter integrated MEMS based electronic devices, specifically in vacuum microelectronic device (VMD) applications.

Improved growth allowed for design and development of novel cold-cathode FE devices utilizing CNT field emitters. A chemical ionization (CI) source based on a CNT-FE electron source was developed and evaluated in a commercial desktop mass spectrometer for explosives trace detection. This work demonstrated the first reported use of a CNT-based ion source capable of collecting CI mass spectra. The CNT-FE source demonstrated low power requirements, pulsing capabilities, and average lifetimes of over 320 hours when operated in constant emission mode under elevated pressures, without sacrificing performance. Additionally, a novel packaged ion source for miniature mass spectrometer applications using CNT emitters, a MEMS based Nier-type geometry, and a Low Temperature Cofired Ceramic (LTCC) 3D scaffold with integrated ion optics were developed and characterized. While previous research has shown other devices capable of collecting ion currents on chip, this LTCC packaged MEMS micro-ion source demonstrated improvements in energy and angular dispersion as well as the ability to direct the ions out of the packaged source and towards a mass analyzer. Simulations and experimental design, fabrication, and characterization were used to make these improvements.

Finally, novel CNT-FE devices were developed to investigate their potential to perform as active circuit elements in VMD circuits. Difficulty integrating devices at micron-scales has hindered the use of vacuum electronic devices in integrated circuits, despite the unique advantages they offer in select applications. Using a combination of particle trajectory simulation and experimental characterization, device performance in an integrated platform was investigated. Solutions to the difficulties in operating multiple devices in close proximity and enhancing electron transmission (i.e., reducing grid loss) are explored in detail. A systematic and iterative process was used to develop isolation structures that reduced crosstalk between neighboring devices from 15% on average, to nearly zero. Innovative geometries and a new operational mode reduced grid loss by nearly threefold, thereby improving transmission of the emitted cathode current to the anode from 25% in initial designs to 70% on average. These performance enhancements are important enablers for larger scale integration and for the realization of complex vacuum microelectronic circuits.

Integrated System Technologies for Modular Trapped Ion Quantum Information Processing

Although trapped ion technology is well-suited for quantum information science, scalability of the system remains one of the main challenges. One of the challenges associated with scaling the ion trap quantum computer is the ability to individually manipulate the increasing number of qubits. Using micro-mirrors fabricated with micro-electromechanical systems (MEMS) technology, laser beams are focused on individual ions in a linear chain and steer the focal point in two dimensions. Multiple single qubit gates are demonstrated on trapped 171Yb+ qubits and the gate performance is characterized using quantum state tomography. The system features negligible crosstalk to neighboring ions (< 3e-4), and switching speeds comparable to typical single qubit gate times (< 2 us). In a separate experiment, photons scattered from the 171Yb+ ion are coupled into an optical fiber with 63% efficiency using a high numerical aperture lens (0.6 NA). The coupled photons are directed to superconducting nanowire single photon detectors (SNSPD), which provide a higher detector efficiency (69%) compared to traditional photomultiplier tubes (35%). The total system photon collection efficiency is increased from 2.2% to 3.4%, which allows for fast state detection of the qubit. For a detection beam intensity of 11 mW/cm2, the average detection time is 23.7 us with 99.885(7)% detection fidelity. The technologies demonstrated in this thesis can be integrated to form a single quantum register with all of the necessary resources to perform local gates as well as high fidelity readout and provide a photon link to other systems.