1,629 research outputs found

    A fabrication process for electrostatic microactuators with integrated gear linkages

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    A surface micromachining process is presented which has been used to fabricate electrostatic microactuators. These microactuators are interconnected with each other and linked to other movable microstructures by integrated gear linkages. The gear linkages consist of rotational and linear gear structures, and the electrostatic microactuators include curved electrode actuators, comb-drive actuators, and axial-gap wobble motors. The micromechanical structures are constructed from polysilicon. Silicon dioxide was used as a sacrificial layer, and silicon nitride was used for electrical insulation. A cyclohexane freeze drying technique was used to prevent problems with stiction. The actuators, loaded with various mechanisms, were successfully driven by electrostatic actuation. The work is a first step toward mechanical power transmission in micromechanical system

    Sacrificial layer process with laser-driven release for batch assembly operations

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    Electrostatic microactuators with integrated gear linkages for mechanical power transmission

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    In this paper a surface micromachining process is presented which has been used to fabricate electrostatic microactuators that are interconnected with each other and linked to other movable microstructures by integrated gear linkages. The gear linkages consist of rotational and linear gear structures and the electrostatic microactuators include curved electrode actuators, comb drive actuators and axial gap wobble motors. The micromechanical structures are constructed from polysilicon. Silicon dioxide has been used as a sacrificial layer and silicon nitride was used for electrical insulation. A cyclohexane freeze drying technique is used to prevent problems with stiction. The actuators, loaded with various mechanisms, have been driven successfully by electrostatic actuation. The work is a first step towards mechanical power transmission in micromechanical system

    Surface micromachined mechanisms and micromotors

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    Electric micromotors are sub-millimeter sized actuators capable of unrestrained motion in at least one degree of freedom. Polysilicon surface micromachining using heavily phosphorus-doped LPCVD polysilicon for the structural material, LPCVD silicon nitride for the electrical isolation and deposited silicon dioxide for the sacrificial material has formed the fabrication technology base for the development of these micromotors. Two polysilicon surface micromachining processes, referred to here as the center-pin and flange, have been demonstrated for the fabrication of passive mechanisms and micromotors. Passive mechanisms such as gear trains, cranks and manipulators have been implemented on silicon. Reported operational micromotors have been of the rotary variable-capacitance salient-pole and harmonic (or wobble) side-drive designs. These micromotors are capable of motive torques in the 10 pN m order of magnitude range. Preliminary progress has been made in studying the operational, friction and wear characteristics of these micromechanical devices. Typical operational voltages have been as low as 37 V and 26 V across 1.5 mu m air gap salient-pole and harmonic micromotors. These excitations correspond to electric field intensities above 10(8) Vm-1 in the micromotor air gaps. Salient-pole and wobble micromotors have been reported to operate at speeds as high as 15000 rpm and 700 rpm, respectively. Micromotor lifetimes of at least many millions of cycles over a period of several days have been reported

    AN INTEGRATED ELECTROMAGNETIC MICRO-TURBO-GENERATOR SUPPORTED ON ENCAPSULATED MICROBALL BEARINGS

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    This dissertation presents the development of an integrated electromagnetic micro-turbo-generator supported on encapsulated microball bearings for electromechanical power conversion in MEMS (Microelectromechanical Systems) scale. The device is composed of a silicon turbine rotor with magnetic materials that is supported by microballs over a stator with planar, multi-turn, three-phase copper coils. The micro-turbo-generator design exhibits a novel integration of three key technologies and components, namely encapsulated microball bearings, incorporated thick magnetic materials, and wafer-thick stator coils. Encapsulated microball bearings provide a robust supporting mechanism that enables a simple operation and actuation scheme with high mechanical stability. The integration of thick magnetic materials allows for a high magnetic flux density within the stator. The wafer-thick coil design optimizes the flux linkage and decreases the internal impedance of the stator for a higher output power. Geometrical design and device parameters are optimized based on theoretical analysis and finite element simulations. A microfabrication process flow was designed using 15 optical masks and 110 process steps to fabricate the micro-turbo-generators, which demonstrates the complexity in device manufacturing. Two 10 pole devices with 2 and 3 turns per pole were fabricated. Single phase resistances of 46Ω and 220Ω were measured for the two stators, respectively. The device was actuated using pressurized nitrogen flowing through a silicon plumbing layer. A test setup was built to simultaneously measure the gas flow rate, pressure, rotor speed, and output voltage and power. Friction torques in the range of 5.5-33”Nm were measured over a speed range of 0-16krpm (kilo rotations per minute) within the microball bearings using spin-down testing methodology. A maximum per-phase sinusoidal open circuit voltage of 0.1V was measured at 23krpm, and a maximum per-phase AC power of 10”W was delivered on a matched load at 10krpm, which are in full-agreement with the estimations based on theoretical analysis and simulations. The micro-turbo-generator presented in this work is capable of converting gas flow into electricity, and can potentially be coupled to a same-scale combustion engine to convert high-density hydrocarbon energy into electrical power to realize a high-density power source for portable electronic systems

    Microturbopompe avec isolation thermique pour cycle Rankine sur puce

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    Les micromoteurs thermiques (Power-MEMS) pourraient offrir une alternative aux batteries pour rĂ©pondre aux besoins d’énergie compacte et distribuĂ©e pour des applications telles que l'Ă©lectronique portable, les robots, les drones et les systĂšmes embarquĂ©s, les capteurs et les actionneurs. La microturbine Ă  vapeur de cycle thermodynamique de Rankine fait partie de ce domaine de micromoteurs. Ce dispositif est destinĂ© Ă  la gĂ©nĂ©ration d’électricitĂ© Ă  petite Ă©chelle Ă  partir de la rĂ©cupĂ©ration de la chaleur perdue. Dans ce contexte, l’objectif de ce travail est la fabrication et la dĂ©monstration expĂ©rimentale d’une microturbopompe Ă  haute tempĂ©rature pour implĂ©menter le cycle de Rankine. Une configuration originale qui intĂšgre l’isolation thermique est, tout d’abord, proposĂ©e. Cette configuration est constituĂ©e d’un empilement de cinq tranches (silicium et verre) pour enfermer un rotor hybride (silicium et verre) supportĂ© par des paliers hydrostatiques. Le rotor est un disque de 4 mm de diamĂštre et de 400 ”m d’épaisseur avec des pales de turbine sur le dessus et une pompe visqueuse Ă  rainures en spirale sur le dessous. Une technique de micromoulage de verre a Ă©tĂ© dĂ©veloppĂ©e dans ce travail pour intĂ©grer du verre dans le rotor comme un matĂ©riau isolant thermiquement. La microturbopompe est fabriquĂ©e avec succĂšs en utilisant les mĂ©thodes de microfabrication des MEMS. Tout d'abord, les paliers hydrostatiques, la turbine et le fonctionnement de la pompe sont caractĂ©risĂ©s, jusqu'Ă  une vitesse de rotation de 100 kRPM. La turbine a fourni 0,16 W de puissance mĂ©canique et le dĂ©bit de la pompe Ă©tait supĂ©rieur Ă  2.55 mg/s. Ensuite, la premiĂšre dĂ©monstration d'une turbopompe MEMS fonctionnant Ă  des tempĂ©ratures Ă©levĂ©es a Ă©tĂ© rĂ©alisĂ©e. Une comparaison a Ă©tĂ© faite avec un rotor non isolĂ© pour prouver l'efficacitĂ© des stratĂ©gies d'isolation thermique. La turbopompe MEMS isolĂ©e a Ă©tĂ© dĂ©montrĂ©e Ă  160°C du cĂŽtĂ© de la turbine. Par extrapolation, la microturbopompe devrait fonctionner jusqu'Ă  une tempĂ©rature de 400°C avant que la tempĂ©rature dans la pompe n'atteigne 100°C. Pour la premiĂšre fois, une microturbopompe pour un fonctionnement Ă  haute tempĂ©rature est fabriquĂ©e et caractĂ©risĂ©e

    Design and Fabrication of a Micro-Bearing Assembly to Study Rotor Friction

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    The objective of this investigation was to design and fabricate a metrology tool for measuring the wear in micro-bearings. The critical component of the tool was a silicon test bed consisting of a bearing shaft and a set of microchannels to direct an air stream onto the fins of a micro-rotor assembled onto the bearing shaft. By driving the micro-rotor pneumatically, surface interactions between the bearing and the rotor can be studied over time. The silicon test bed mates to a custom aluminum chuck which has provisions for sealing the test bed and supplying air pressure from an external source. The silicon test bed was successfully fabricated by bulk micromachining using Deep Reactive Ion Etching (DRIE). Test rotors were also fabricated using DRIE and manually placed onto the bearing shaft of the test bed. A glass cover slide, held in place by the aluminum chuck, was used to seal the top of the test bed. Test rotors were successfully rotated using a minimum input air pressure of 0.5 psi

    Comb-drive actuators for large displacements

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    The design, fabrication and experimental results of lateral-comb-drive actuators for large displacements at low driving voltages is presented. A comparison of several suspension designs is given, and the lateral large deflection behaviour of clamped - clamped beams and a folded flexure design is modelled. An expression for the axial spring constant of folded flexure designs including bending effects from lateral displacements, which reduce the axial stiffness, is also derived. The maximum deflection that can be obtained by comb-drive actuators is bounded by electromechanical side instability. Expressions for the side-instability voltage and the resulting displacement at side instability are given. The electromechanical behaviour around the resonance frequency is described by an equivalent electric circuit. Devices are fabricated by polysilicon surface micromachining techniques using a one-mask fabrication process. Static and dynamic properties are determined experimentally and are compared with theory. Static properties are determined by displacement-to-voltage, capacitance-to-voltage and pull-in voltage measurements. Using a one-port approach, dynamic properties are extracted from measured admittance plots. Typical actuator characteristics are deflections of about at driving voltages around 20 V, a resonance frequency around 1.6 kHz and a quality factor of approximately 3

    Tribology of Microball Bearing MEMS

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    This dissertation explores the fundamental tribology of microfabricated rolling bearings for future micro-machines. It is hypothesized that adhesion, rather than elastic hysteresis, dominates the rolling friction and wear for these systems, a feature that is unique to the micro-scale. To test this hypothesis, specific studies in contact area and surface energy have been performed. Silicon microturbines supported on thrust bearings packed with 285 ”m and 500 ”m diameter stainless steel balls have undergone spin-down friction testing over a load and speed range of 10-100mN and 500-10,000 rpm, respectively. A positive correlation between calculated contact area and measured friction torque was observed, supporting the adhesion-dominated hysteresis hypothesis. Vapor phase lubrication has been integrated within the microturbine testing scheme in a controlled and characterized manner. Vapor-phase molecules allowed for specifically addressing adhesive energy without changing other system properties. A 61% reduction of friction torque was observed with the utilization of 18% relative humidity water vapor lubrication. Additionally, the relationship between friction torque and normal load was shown to follow an adhesion-based trend, highlighting the effect of adhesion and further confirming the adhesion-dominant hypothesis. The wear mechanisms have been studied for a microfabricated ball bearing platform that includes silicon and thin-film coated silicon raceway/steel ball materials systems. Adhesion of ball material, found to be the primary wear mechanism, is universally present in all tested materials systems. Volumetric adhesive wear rates are observed between 4x10^-4 ”m^3/mN*rev and 4x10^-5 ”m3/mN*rev were determined by surface mapping techniques and suggest a self-limiting process. This work also demonstrates the utilization of an Off-The-Shelf (OTS) MEMS accelerometer to confirm a hypothesized ball bearing instability regime which encouraged the design of new bearing geometries, as well as to perform in situ diagnostics of a high-performance rotary MEMS device. Finally, the development of a 3D fabrication technique with the potential of significantly improving the performance of micro-scale rotary structures is described. The process was used to create uniform, smooth, curved surfaces. Micro-scale ball bearings are then able to be utilized in high-speed regimes where load can be accommodated both axially and radially, allowing for new, high-speed applications. A comprehensive exploration of the fundamental tribology of microball bearing MEMS has been performed, including specific experiments on friction, wear, lubrication, dynamics, and geometrical optimization. Future devices utilizing microball bearings will be engineered and optimized based on the results of this dissertation
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