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Microelectromechanical Systems, Journal of

Issue 2 • Date April 2004

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Displaying Results 1 - 25 of 30
  • Table of contents

    Page(s): c1 - c4
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    Freely Available from IEEE
  • Journal of Microelectromechanical Systems publication information

    Page(s): c2
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  • A curved-beam bistable mechanism

    Page(s): 137 - 146
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB) |  | HTML iconHTML  

    This paper presents a monolithic mechanically-bistable mechanism that does not rely on residual stress for its bistability. The typical implementation of this mechanism is two curved centrally-clamped parallel beams, hereafter referred to as "double curved beams". Modal analysis and finite element analysis (FEA) simulation of the curved beam are used to predict, explain, and design its bistable behavior. Microscale double curved beams are fabricated by deep-reactive ion etching (DRIE) and their test results agree well with the analytic predictions. Approaches to tailor the bistable behavior of the curved beams are also presented. View full abstract»

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  • A low-temperature thin-film electroplated metal vacuum package

    Page(s): 147 - 157
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    This paper presents a packaging technology that employs an electroplated nickel film to vacuum seal a MEMS structure at the wafer level. The package is fabricated in a low-temperature (<250°C) 3-mask process by electroplating a 40-μm-thick nickel film over an 8-μm sacrificial photoresist that is removed prior to package sealing. A large fluidic access port enables an 800×800 μm package to be released in less than three hours. MEMS device release is performed after the formation of the first level package. The maximum fabrication temperature of 250°C represents the lowest temperature ever reported for thin film packages (previous low ∼400°C). Implementation of electrical feedthroughs in this process requires no planarization. Several mechanisms, based upon localized melting and Pb/Sn solder bumping, for sealing low fluidic resistance feedthroughs have been investigated. This package has been fabricated with an integrated Pirani gauge to further characterize the different sealing technologies. These gauges have been used to establish the hermeticity of the different sealing technologies and have measured a sealing pressure of ∼1.5 torr. Short-term (∼several weeks) reliability data is also presented. View full abstract»

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  • A self-acting gas thrust bearing for high-speed microrotors

    Page(s): 158 - 164
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    Micromachines rotating at high speeds require low drag bearings with adequate load capacity and stability. Such bearings must be compatible with the capabilities of microfabrication technology. A self-acting (hydrodynamic) gas thrust bearing was designed, fabricated and tested on a silicon microturbine. Conventional thrust bearing design techniques were adapted from macroscale literature. Microbearing design charts are presented that relate bearing performance to geometry. Such bearings exhibit a design tradeoff between load bearing capability and maximum operating speed (as limited by instabilities). The specific geometry described herein was intended to replace externally pressurized, hydrostatic thrust bearings in an existing device (a 4-mm-diameter silicon microturbine), thus the hydrodynamic bearing design was constrained to be compatible in geometry and fabrication process. The final design consisted of 2.2-μm deep by 40-μ wide spiral grooves around the 700-μm diameter bearing. The bearings were fabricated in silicon with standard RIE and DRIE techniques. Test devices demonstrated lift-off and operation up to 450,000 rpm with a load capacity of 0.03 N. Measurements of load capacity and stiffness were consistent with the analysis. View full abstract»

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  • MEMS-based solid propellant microthruster design, simulation, fabrication, and testing

    Page(s): 165 - 175
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    A new design concept of solid propellant microthruster is proposed for micropropulsion applications. Modeling and simulation have been performed before the fabrication of the microthrusters using MEMS technologies. At sea level, the predicted thrust magnitudes range from 0.76 mN to 4.38 mN and the estimated total impulses range from 1.16×10-4 N·s to 4.37×10-4 N·s using HTPB/AP/AL as the propellant. In space, the predicted thrust magnitudes range from 9.11 mN to 26.92 mN and the estimated total impulses range from 1.25×10-3 N·s to 1.70×10-3 N·s. Single microthruster, microthruster layers and arrays have been successfully fabricated. Preliminary testing for microcombustion is conducted to verify the feasibility of the novel design. Continuous combustion has been achieved after igniting the solid propellant and successful production of thrust has been verified by the microthruster displacement. View full abstract»

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  • Microassembly of 3-D microstructures using a compliant, passive microgripper

    Page(s): 176 - 189
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    This paper describes a novel microassembly system that can be used to construct out-of-plane three-dimensional (3-D) microstructures. The system makes use of a surface-micromachined microgripper that is solder bonded to a robotic manipulator. The microgripper is able to grasp a micropart, remove it from the chip, reorient it about two independent axes, translate it along the x, y and z axes to a secondary location, and join it to another micropart. In this way, out-of-plane 3-D microstructures can be assembled from a set of initially planar and parallel surface micromachined microparts. The microgripper is 380 × 410 μm in size. It utilizes three geometric features for operation: 1) compliant beams to allow for deflection at the grasping tips; 2) self-tightening geometry during grasping; and 3) 3-D interlocking geometry to secure a micropart after the grasp. Each micropart has three geometric features built into its body. The first is the interlock interface feature that allows it to be grasped by the microgripper. The second is a tether feature that secures the micropart to the substrate, and breaks away after the microgripper has grasped the micropart. The third is the snap-lock feature, which is used to join the micropart to other microparts. View full abstract»

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  • The MEMSNAS process: microloading effect for micromachining 3-D structures of nearly all shapes

    Page(s): 190 - 199
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    We propose a technological process for microfabrication of three-dimensional (3-D) structures with nearly all shapes. This is a one-mask process that uses equipment, widespread in the microelectronics laboratories and industry. The main idea is to take advantage from the microloading effect of reactive ion etching (RIE) in order to obtain multiple levels of heights in an array of microholes of different diameters. A 3-D profile results from an overlap of the neighboring microholes due to the isotropic nature of the etching. The final continuous and smooth 3-D structure is obtained after removal of the mask material and a second isotropic RIE step. This fabrication process was validated with the realization of various 3-D structures including microlenses, etched in a 30 μm deep cavity, with 375 μm in radius and 10 μm in height (sag). The resulting structures have shown a roughness down to 25 nm. A quantitative experimental study led to the calibration of three different processes and to an empirical theoretical model, which can serve as a basis of design rules for further fabrication of 3-D microstructures. View full abstract»

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  • Mechanical characterization of polysilicon through on-chip tensile tests

    Page(s): 200 - 219
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    Two new types of on-chip tests have been designed in order to evaluate the elastic Young modulus and the fracture strength of polysilicon used in microelectromechanical systems (MEMS). The former is a pure tension test, while the latter is a single-edge-notched tension test. The actuation in both tests is obtained by means of an ad hoc designed layout of parallel plates capacitors applying sufficiently high forces to reach significant strains in the tensile specimens and complete failure of the notched specimens. The pure tension tests on 20 specimens showed a low dispersion and gave a Young modulus for the polysilicon of 143 GPa. A total of 92 notched specimens were tested up to failure. The experimental results, supported by finite-element simulations, gave a value of the maximum stress for the notched specimens in the range 4144-4568 MPa. View full abstract»

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  • Measurement system for low force and small displacement contacts

    Page(s): 220 - 229
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    To support the continued miniaturization of electrical contacts in multichip systems, three-dimensional (3-D) systems, wafer probe cards, and MEMS relays, there is a need for combined measurements of electrical and mechanical phenomena during contact formation. We have carried out a study of electrical contacts in the nN-mN force range for future generation probe cards and novel electronic packaging. One critical phenomenon in the contact formation process is nm-scale deformation of the material layers. To directly study this contact displacement, we have designed a measurement system comprised of a piezoresistive cantilever and an optical interferometer. Together, this system simultaneously measures contact resistance (mOhm to kOhm), force (nN to mN), and displacement (nm-μm). These measurements allow the first direct observation of contact mechanical behavior in this important application range. These measurements show that asperities at the contact surface dominate the behavior of the contacts, causing deviations from the Hertzian model of elastic contacts. This paper describes the design and construction of this apparatus, and the operation in a contact mechanics experiment. View full abstract»

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  • Anelasticity and damping of thin aluminum films on silicon substrates

    Page(s): 230 - 237
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    A new dynamic measurement system has been developed to investigate damping in thin metal films. This system includes a vacuum chamber, in which a free-standing bilayer cantilever sample is vibrated using an electrostatic force, and a laser interferometer to measure the displacement and velocity of the sample. With this equipment, internal friction as low as 10-5 in micrometer thick metal films in a temperature range from 300 to 750 K can be measured. Free-standing cantilevers with different frequencies have been fabricated using well-established integrated circuit (IC) fabrication processes. The cantilevers consist of thin metal films on thicker Si substrates, which exhibit low damping. From measurements of internal friction of Al thin films at various temperatures and frequencies, it is possible to study relaxation processes associated with grain boundary diffusion. The activation energy calculated from the damping data is 0.57 eV, which is consistent with previous research. This value suggests that the mechanism of internal friction in pure Al films involves grain boundary diffusion controlled grain boundary sliding. A model to describe these damping effects has been developed. By deriving an expression for the diffusional strain rate using a two-dimensional (2-D) Coble creep model, and modifying the conventional standard linear solid model for the case of bending, it is possible to give a good account of the observed damping. View full abstract»

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  • High-fidelity modeling of MEMS resonators. Part I. Anchor loss mechanisms through substrate

    Page(s): 238 - 247
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    A computational model is developed for the prediction of wave propagation in the substrate of a MEMS resonator to study energy loss mechanisms from the vibrating beams to the substrate, viz., anchor loss. The model employs a modified classical Fourier transform method under periodic excitations at the anchor area. The present substrate model, when applied to a typical commercially fabricated substrate, estimates that the anchor loss of an ends-anchored resonator with its center frequency of 50 MHz can reach as high as 0.05% in terms of equivalent damping ratio. Anchor loss versus resonator center frequency is assessed by varying the beam dimension, which predicts that anchor loss increases a hundredfold for every tenfold increase in resonator center frequency in the case of two ends-anchored beam resonators. The substrate model has been integrated into a coupled beam-substrate-electrostatics model and validated with experimental data. Development of the detailed coupled-physics model and its validation is presented in Part II as a companion paper. View full abstract»

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  • High-fidelity modeling of MEMS resonators. Part II. Coupled beam-substrate dynamics and validation

    Page(s): 248 - 257
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    A computational multiphysics model of the coupled beam-substrate-electrostatic actuation dynamics of MEMS resonators has been developed for the model-based prediction of Q-factor and design sensitivity studies of the clamped vibrating beam. The substrate and resonator beam are modeled independently and then integrated by enforcing their interface compatibility condition and the force equilibrium to arrive at the multiphysics model. The present model has been validated with several reported single-beam clamped resonators. The validated model indicates that: the anchor loss is primarily engendered through coupling between the resonant modes and the waves propagating through the substrate inner layers; the resonant frequency of the beam decreases up to 5% due to substrate flexibilities interacting with beam at the anchors; and, for a given design the beam mass and its relative compliance with respect to the substrate are key parameters that influence the Q-factor degradation. In addition, the coupled model has also been used to predict the Q-factor of a paired-beam mechanical filter device with high fidelity when compared with the experimentally observed Q-factor. View full abstract»

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  • A micromachined 2 × 2 optical switch aligned with bevel-ended fibers for low return loss

    Page(s): 258 - 263
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    This paper presents the design and optical performance characteristics of a micromachined 2 × 2 optical switch with low return loss for an optical add-drop application. The switch is equipped with four optical fibers beveled at 8°. An intentional lateral offset was introduced to align the refracted light at the input fiber-air interface with output fibers. A micromirror was actuated into the optical path by an electrostatic comb actuator to change the direction of the input optical signal. The optical switch was fabricated using silicon deep reactive ion etching (DRIE) of silicon-on-insulator (SOI) wafers. Optical performance measurements of the fabricated optical switch revealed that the time dependent loss (TDL), polarization dependent loss (PDL), and wavelength dependent loss (WDL) were -0.04 dB, -0.05 dB and -0.71 dB, respectively. The switching time was within 5 ms for a 24-V electrical step signal. Because the beveled ends of the optical fibers kept the propagated light from reflecting backward into the input fiber, the return losses were just -43 dB. This return loss was used to theoretically analyze a model of the beveled end by considering backscattering due to the surface roughness, which thereby was determined to be about 41 nm. View full abstract»

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  • Application of a multilayered magnetostrictive film to a micromachined 2-D optical scanner

    Page(s): 264 - 271
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    A novel two-dimensional (2-D) optical scanner has been designed, manufactured and characterized. This scanner features a large mirror (8×6 mm) and is therefore suitable for industrial applications where cheap optical sources and lenses are requested. This scanner uses a multilayer film for its actuation. This film is well known for its high magnetostriction. The mechanical design has been optimized using conventional mechanical considerations as well as finite-element simulations. The device has been characterized in two configurations. Depending on the direction of the applied magnetic field, the magnetostrictive properties of the active film or the electromagnetic force are selectively used. Using this last, total optical deflection angles of 32° and 11° for an applied magnetic field of 0.3 mT are obtained. The ratio of the corresponding resonant frequencies is around 4.5, allowing a nice scanning pattern. Compared to our previous prototype on the same project , the mechanical-magnetic sensitivity has been improved by about a factor 24 when the magnetostriction is used, and by about a factor 75 when the electromagnetic force is used. View full abstract»

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  • MEMS tilt-mirror spatial light modulator for a dynamic spectral equalizer

    Page(s): 272 - 278
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    This paper presents a linear array of tilting mirrors used to attenuate the various wavelengths in a DWDM optical signal. Attenuation of 21 dB at snap-down was achieved by the tilting mirrors, substituting for a liquid crystal spatial light modulator (SLM) in a commercial dynamic spectral equalizer (DSE). Linear fill factor of 92% was achieved, allowing closely spaced wavelength channels to be individually attenuated. A two layer polysilicon process with a thick epi-poly mirror was used to fabricate the SLM. Initial mirrors had a radius of curvature of 25 cm. A novel accelerated HF-H2SO4 etch allowed 100 μm wide mirrors to be undercut in 12 min with no etch release holes. View full abstract»

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  • Low-voltage, large-scan angle MEMS analog micromirror arrays with hidden vertical comb-drive actuators

    Page(s): 279 - 289
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    This paper reports on novel polysilicon surface-micromachined one-dimensional (1-D) analog micromirror arrays fabricated using Sandia's ultraplanar multilevel MEMS technology-V (SUMMiT-V) process. Large continuous DC scan angle (23.6° optical) and low-operating voltage (6 V) have been achieved using vertical comb-drive actuators. The actuators and torsion springs are placed underneath the mirror (137×120 μm2) to achieve high fill-factor (91%). The measured resonant frequency of the mirror ranges from 3.4 to 8.1 kHz. The measured DC scanning characteristics and resonant frequencies agree well with theoretical values. The rise time is 120 μs and the fall time is 380 μs. The static scanning characteristics show good uniformity (<±3.2%) for a 1 × 10 array with a mirror pitch of 150 μm. The mechanical crosstalk between adjacent mirrors is less than 37 dB. These micromirror arrays have applications in 1×N wavelength-selective switches and N×N wavelength-selective crossconnects in wavelength-division multiplexing (WDM) networks. View full abstract»

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  • A 2-D microcantilever array for multiplexed biomolecular analysis

    Page(s): 290 - 299
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    An accurate, rapid, and quantitative method for analyzing variety of biomolecules, such as DNA and proteins, is necessary in many biomedical applications and could help address several scientific issues in molecular biology. Recent experiments have shown that when specific biological reactions occur on one surface of a microcantilever beam, the resulting changes in surface stress deflect the cantilever beam. To exploit this phenomenon for high-throughput label-free biomolecular analysis, we have developed a chip containing a two-dimensional (2-D) array of silicon nitride cantilevers with a thin gold coating on one surface. Integration of microfluid cells on the chip allows for individual functionalization of each cantilever of the array, which is designed to respond specifically to a target analyte. An optical system to readout deflections of multiple cantilevers was also developed. The cantilevers exhibited thermomechanical sensitivity with a standard deviation of seven percent, and were found to fall into two categories-those whose deflections tracked each other in response to external stimuli, and those whose did not due to drift. The best performance of two "tracking" cantilevers showed a maximum difference of 4 nm in their deflections. Although "nontracking" cantilevers exhibited large differences in their drift behavior, an upper bound of their time-dependent drift was determined, which could allow for rapid bioassays. Using the differential deflection signal between tracking cantilevers, immobilization of 25mer thiolated single-stranded DNA (ssDNA) on gold surfaces produced repeatable deflections of 80 nm or so on 0.5-μm-thick and 200-μm-long cantilevers. View full abstract»

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  • High-performance inductors using capillary based fluidic self-assembly

    Page(s): 300 - 309
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    In this paper, a batch microfabrication process is presented for creating high aspect ratio, micron-sized helical and toroidal inductors with Q greater than or equal to 50 at multi-GHz frequencies. With a maximum processing temperature of only 220°C, the inductors can be fabricated on top of standard CMOS wafers. This process can also be used to create "inductor chiplets", which are polymer-encapsulated inductors with the same form factor as an EIA (Electronics Industries Association) standard 0201 surface mount device. The chiplets can be assembled onto CMOS wafers using a fluidic microassembly technique. This technique allows for multiple electrical interconnects to the inductor chiplets. The 40-μm gap between the substrate and assembled inductor increases the Q by a factor of ∼3 compared to as-fabricated inductors. Assembled and as-fabricated inductors have been characterized on similar substrates and have maximum Q values of 50 and 15 with resonant frequencies of 10 GHz and 9 GHz, respectively. Performance of the assembled inductors is nearly comparable to that of inductors as fabricated and tested on quartz substrates. View full abstract»

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  • Computational study of band-crossing reactions

    Page(s): 310 - 322
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    A numerical study of band-crossing reactions is conducted using a quasi-one-dimensional (1-D) computational model that accounts for species bulk advection, electromigration velocities, diffusion, and chemical reaction. The model is used to simulate chemical reactions between two initially distinct sample zones, referred to as "bands," that cross each other due to differences in electromigration velocities. The reaction is described in terms of a single step, reversible mechanism involving two reactants and one product. A parametric study is first conducted of the behavior of the species profiles, and results are interpreted in terms of the Damköhler number and of the ratios of the electromigration velocities of the reactant and product. Computed results are then used to explore the possibility of extracting forward and backward reaction rates based on time resolved observation of integral moments of species concentrations. In particular, it is shown that in the case of fast reactions, robust estimates can be obtained for high forward rates, but that small reverse rates may not be accurately observed. View full abstract»

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  • Cross-coupling errors of micromachined gyroscopes

    Page(s): 323 - 331
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    A model is developed for the response of a micromachined, rotary gyroscope subject to a general input motion. The governing equations are formulated for weakly nonlinear oscillations of the rotor, suspended above the moving substrate via elastic beams. The method of multiple scales is used to separate the slow and fast responses. This approach allows quick computation of the long-term behavior of the rotor without the need to integrate over fast oscillations. The power of the model to evince cross-coupling errors is demonstrated through examples. View full abstract»

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  • The electromechanical response of multilayered piezoelectric structures

    Page(s): 332 - 341
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    The constitutive equations of multilayered piezoelectric structures are derived in a new form. In this form, the electromechanical coupling is presented as an additional stiffness matrix. This matrix is a true property of the piezoelectric structure and is independent of specific mechanical boundary conditions that may apply to the structure. A novel model of the electromechanical response of such structures is presented. This model accounts for the three-dimensional (3-D) kinematics of the structure deformation. Solution of example problems using the new model shows excellent agreement with full 3-D finite element simulations. These solutions are also compared to the results of previous two-dimensional (2-D) model approximations presented in literature, and the inaccuracies associated with these previous models are discussed. View full abstract»

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  • Analysis and analytical modeling of static pull-In with application to MEMS-based voltage reference and process monitoring

    Page(s): 342 - 354
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    The pull-in voltage of one- and two-degrees-of-freedom (DOF) structures has been symbolically and numerically analyzed with respect to drive mode dependence and hysteresis. Moreover, the time and temperature stability has been investigated and tested. Modeling results have been applied in the design of both folded-spring-suspended 1-DOF structures and single-side-clamped 2-DOF beams with a nominal pull-in voltage in the 5-10 V range and fabricated in an epi-poly process. Asymmetrically driven structures reveal pull-in close to the value predicted by the model (Vpi 1-DOF is 4.65 V analytically simulated and 4.56 V measured; Vpi 2-DOF is 9.24 V analytically simulated, 9.30 V in FEM and 9.34 V measured). Also the hysteresis is in close agreement (release voltage, Vr, 1-DOF is 1.41 V analytically simulated and 1.45 V measured; Vr 2-DOF is 9.17 V analytically simulated, 9.15 V in FEM and 9.27 V measured). In symmetrically operated devices the differences between the computed and measured Vpi and Vr are much larger and are due to process dependencies, which make these devices very suitable for process monitoring. The 2-DOF asymmetrically operated device is the most suitable for MEMS-based voltage reference. The stability in time is limited by charge build-up and calls for a 100-hour initial burn-in. Temperature dependence is -100 μV/K at Vpi≈5 V, however, is calculable and thus can be corrected or compensated. View full abstract»

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  • BESOI-based integrated optical silicon accelerometer

    Page(s): 355 - 364
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    The design, simulation, fabrication and characterization of a new integrated optical accelerometer is presented in this paper. The reduction of fabrication, packaging and thermomechanical stresses are considered by keeping the weak mechanical parts free of stresses. The mechanical sensor consists on a quad beam structure with one single mass. In addition, there are two waveguides on the frame of the chip self-aligned to one on the mass of the accelerometer. Four lateral beams increase the mechanical sensitivity and allow the flat displacement of the optical waveguides on the mass. The working principle is based on the variation of the output light intensity versus the acceleration due to the misalignment of the waveguides. The devices have been optimized by the finite-element method to obtain a mechanical sensitivity of 1 μm/g. The fabrication technology is based on BESOI wafers combining bulk an surface micromachining. Moreover, machined glass wafers with cavities are bonded to the silicon wafer for packaging and damping control. Special packaging considerations as dicing, polishing and alignment are also presented. Optical measurements at 633 nm shown an optical sensitivity of 2.3 dB/g for negative and 1.7 dB/g for positive acceleration. This difference in the sensitivity has been demonstrated as a consequence of the passivation layer located over the core of the waveguides. View full abstract»

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  • Self-aligning MEMS in-line separable electrical connector

    Page(s): 365 - 376
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    A MEMS in-line separable connector containing features for precision self-alignment is demonstrated. The concept relies on sliding connection between female and male halves to induce vertical deflections of a set of flexible conductors and establish stable electrical contacts. Electrodeposited photoresist is used to fabricate thick, nonplanar conductors, shaped by a silicon substrate that has previously been terraced by anisotropic etching. Further etched features ensure transverse and vertical self-alignment between conductor elements during mating. Prototype 10-way connectors are demonstrated with 200 μm wide conductors on a 250-μm pitch. Mechanical reliability of contacts during repeated mating and demating is demonstrated, and initial measurement of contact resistance reveals an encouraging value of 30 mΩ. View full abstract»

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Aims & Scope

The topics of interest include, but are not limited to: devices ranging in size from microns to millimeters, IC-compatible fabrication techniques, other fabrication techniques, measurement of micro phenomena, theoretical results, new materials and designs, micro actuators, micro robots, micro batteries, bearings, wear, reliability, electrical interconnections, micro telemanipulation, and standards appropriate to MEMS. Application examples and application oriented devices in fluidics, optics, bio-medical engineering, etc., are also of central interest.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Christofer Hierold
ETH Zürich, Micro and Nanosystems