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Microelectromechanical Systems, Journal of

Issue 3 • Date June 2010

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Displaying Results 1 - 25 of 36
  • Table of contents

    Page(s): C1 - C4
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  • Journal of Microelectromechanical Systems publication information

    Page(s): C2
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    Freely Available from IEEE
  • Thermally Actuated Omnidirectional Walking Microrobot

    Page(s): 433 - 442
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (984 KB) |  | HTML iconHTML  

    We describe a walking microrobot that is propelled by cilialike thermal bimorph actuator arrays. The robot consists of two actuator array chips, each having an 8 × 8 array of “motion pixels,” which are composed of four orthogonally oriented cilia. Each group of unidirectional cilia is controlled independently for each chip, which provides planar motion with three degrees of freedom (x, y, θ). The robot is approximately 3 cm in length, 1 cm in width, and 0.9 mm in height and has a mass of 0.5 g. By varying the actuation frequency and motion gait strategy, the direction and velocity of the motion can be controlled. In this paper, we present the system architecture, control mechanism, and modeling of the robot, as well as experimental results, during linear and rotary motion. The robot can carry loads up to seven times its own mass, and it can operate at speeds up to 250 μm/s with step sizes from 1 to 4 μm. View full abstract»

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  • Novel Capacitive Pressure Sensor

    Page(s): 443 - 450
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (423 KB) |  | HTML iconHTML  

    A new microelectromechanical-systems capacitive pressure sensor with extremely high sensitivity (2.24 ??F/kPa) is introduced. The sensor essentially consists of a small drop of mercury and a flat aluminum electrode that are separated by a 1 ??m-thick layer of Barium Strontium Titanate (a high dielectric-constant ceramic). The assembly constitutes a parallel-plate capacitor where the surface area of the electrodes is variable to a high degree. The mercury drop is pressured by a small corrugated metal diaphragm. As the electrode area of the parallel-plate capacitor varies, a total change in capacitance of more than 6 ??F is obtained. View full abstract»

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  • A Bidirectional Two-Axis Electrostatic MEMS Positioning System

    Page(s): 451 - 457
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (825 KB) |  | HTML iconHTML  

    We report on the design, fabrication, and testing of a bidirectional two-axis MEMS positioning system that is used to move a stage. Sandia National Laboratories' MEMS foundry process was utilized for the fabrication of the device; this process incorporates five layers of polysilicon and four sacrificial layers of silicon dioxide. The positioning assembly consists of a pin and slotted-arm arrangement, wherein the pin is constrained between the slotted arms and the positioning of the pin is achieved by identical electrostatic drives on both axes. The electrostatic drives consist of a comb drive interfaced with a compliant-mechanism-based distance multiplier. The stage is connected to a cantilever arm extending from the positioning pin. The crosstalk between the X- and Y-axes was less than 0.3 ??m through displacements of ~30 ??m in both X- and Y-directions. The displacement shows a quadratic relationship with the applied voltage. View full abstract»

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  • A Lateral-Axis Microelectromechanical Tuning-Fork Gyroscope With Decoupled Comb Drive Operating at Atmospheric Pressure

    Page(s): 458 - 468
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1993 KB) |  | HTML iconHTML  

    In this paper, a silicon bulk micromachined lateral-axis tuning-fork gyroscope (TFG) with a decoupled comb drive and torsional sensing comb capacitors is presented. The novel driving comb capacitors are used to suppress the parasitic out-of-plane electrostatic force and, hence, can decouple the mechanical crosstalk from the sensing mode to the driving mode in a simple manner. The torsional sensing combs are designed to differentially sense the out-of-plane rotational moment and are arranged centroidally to be immune to fabrication imperfections for good linearity and electrostatic force balancing. The torsional sensing combs adopted in the TFG help to lower the air damping of the sensing mode while the driving mode of the gyroscope is dominated by slide-film air damping; hence, it can work even at atmospheric pressure. The process for this lateral-axis gyroscope can also be used to fabricate z-axis gyroscopes; therefore, low-cost miniature monolithic inertial measurement units can be realized without vacuum packaging. The TFG is tested at atmospheric pressure with a sensitivity of 17.8 mV/??/s and a nonlinearity of 0.6% in a full-scale range of 1000??/s. The bias stability is measured to be 0.05??/s (1 ??) in 30 min with an equivalent noise angular rate of 0.02??/s/Hz1/2. View full abstract»

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  • Chip-Scale Quadrupole Mass Filters for Portable Mass Spectrometry

    Page(s): 469 - 483
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    We report the design, fabrication, and characterization of a new class of chip-scale quadrupole mass filter (QMF). The devices are completely batch fabricated using a wafer-scale process that integrates the quadrupole electrodes, ion optics, and housing into a single monolithic block. This process eliminates the electrode-to-housing misalignments inherent in other QMFs and enables the implementation of complex device architectures. To achieve the reported integration, 1 mm ?? 1 mm square electrodes of heavily doped silicon were utilized, resulting in quadrupoles with an effective aperture radius of 0.707 mm and a length of 30 mm. Mass filtering was demonstrated with this unconventional device showing a mass range of 650 amu and a resolution of ~30 at a drive frequency of 1.8 MHz. When operated in the second stability region at 2.0 MHz and a mass range of 50 amu, a peak width of 0.3 amu was achieved at mass 28, showing a resolution of ~90. This paper introduces operation in the second stability region as a reliable method for turning QMFs with less than ideal electrode geometries into high-performance devices. View full abstract»

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  • CNT-Based MEMS/NEMS Gas Ionizers for Portable Mass Spectrometry Applications

    Page(s): 484 - 493
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    We report the fabrication and experimental characterization of a carbon nanotube (CNT)-based MEMS/NEMS electron impact gas ionizer with an integrated extractor gate for portable mass spectrometry. The ionizer achieves low-voltage ionization using sparse forests of plasma-enhanced chemical-vapor-deposited CNTs as field emitters and a proximal extractor grid with apertures aligned to the CNT forests to facilitate electron transmission. The extractor gate is integrated to the ionizer using a high-voltage MEMS packaging technology based on Si springs defined by deep reactive ion etching. The ionizer also includes a high-aspect-ratio silicon structure (??foam) that facilitates sparse CNT growth and also enables uniform current emission. The devices were tested as field emitters in high vacuum (10-8 torr) and as electron impact ionizers using argon at pressures of up to 21 mtorr. The experimental data show that the MEMS extractor gate transmits up to 66% of the emitted current and that the ionizers are able to produce up to 0.139 mA of ion current with up to 19% ionization efficiency while consuming 0.39 W. View full abstract»

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  • Design, fabrication, and application of bio-implantable acoustic power transmission

    Page(s): 494 - 502
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    Fully packaged acoustic power receivers are introduced. They can provide electronic energy to other implanted devices by receiving an external acoustic wave generated from the skin surface of the subcutaneous tissue. Piezoelectric ceramics make the internal devices of the receivers, and they are directly charged, converting pressure into an extractable electrical energy. Moreover, cohesive gel is used to package the internal devices, and the packages are biocompatible and sufficiently soft to absorb the incident wave that is generated at the skin surface. Additionally, the effects of the shape of the scattering package and ratio of the stiffness of the package to that of the tissue are considered in designing the receivers. The dominant frequencies and the energy efficiency of the receivers are measured in the very streaky pork, which is used to simulate human subcutaneous tissue. The results indicate that the spherical packaging is preferable to the cubic packaging when buried in the muscular layer. The maximum efficiency of the power transmission is found to be -48.2 dB, using the spherical package in the muscular layer of the streaky pork. View full abstract»

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  • Micromechanical IBARs: Tunable High- Q Resonators for Temperature-Compensated Reference Oscillators

    Page(s): 503 - 515
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2066 KB) |  | HTML iconHTML  

    This paper presents a unique capacitive micromechanical resonator and oscillator architecture for temperature-compensated frequency references. The I-shaped bulk acoustic resonator (IBAR) is designed to have excellent electrical tunability for temperature compensation (TC) and dynamic frequency control. High quality factor and low motional resistance are also achieved. The applicable range of frequencies is 1-30 MHz, in which quality factors exceeding 100 000 have been measured. Resonator metrics, including the electrostatic tuning coefficient, normalized dynamic stiffness, and relative dynamic compliance, are introduced. A small-signal resistance in the resonator is reported and explained. This unexpected resistance is beneficial for oscillator functionality over a large temperature range. The interface IC, inclusive of all blocks for sustaining oscillations and TC, is also presented. A two-chip 6-MHz oscillator with a temperature stability of 39 ppm over 100??C is demonstrated. The interface IC consumes 1.9 mW. View full abstract»

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  • Micromechanical IBARs: Modeling and Process Compensation

    Page(s): 516 - 525
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    Manufacturability is a major challenge before widespread adoption of micromechanical resonators as frequency references. In this paper, the limits of frequency accuracy for a silicon resonator are investigated. The factors to these limits, including starting materials and process variations, are investigated. Design for manufacturing utilizing process compensation (PC) is presented. The I-shaped bulk acoustic resonator (IBAR) is considered since it has features that enable PC. A lumped-element model for the IBAR is developed. Assuming that variations in resonator geometry are locally systematic, the effect of process bias on resonator frequency is modeled. A procedure to obtain low sensitivity to process variations is explained. Process bias variation (i.e., skew) on a 10-MHz design is replicated with electron beam lithography. PC of a micromechanical resonator, confirmed with experimental data, is demonstrated for the first time. From the observations, strategies for obtaining absolute single-digit ppm frequency accuracy are presented. View full abstract»

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  • Experimental Validation of Mixed Electromechanical and Electromagnetic Modeling of RF-MEMS Devices Within a Standard IC Simulation Environment

    Page(s): 526 - 537
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2009 KB) |  | HTML iconHTML  

    The validity and applicability of a high-level simulation approach of radio-frequency microelectromechanical-system (RF-MEMS) devices, based on a library of analytical compact models of elementary MEMS components, are investigated through an extensive comparison between simulation results and measurements of some representative devices (variable capacitors and series ohmic switches). The in-house developed simulation tool is implemented in a standard IC simulation environment supporting behavioral description capabilities. The devices are built in a silicon substrate technology with suspended gold membranes. We analyze the mechanical, electrical, and RF response of the devices. The RF behavior is modeled by extracting a lumped element network from measured S-parameters (scattering-parameters) to account for parasitic effects and by wrapping this network around the intrinsic MEMS device simulated with the compact models. We show that an accuracy within 5% is obtained in all considered physical domains and conditions, provided that some effective parameters (including the residual air gap in the actuated state and the RF parasitic elements) are properly extracted from measurements and accounted for in the simulations. The main factors limiting the model's predictive capability are due to process nonidealities, such as plate bending due to residual stress gradient, oxide charging, surface roughness, and suspended membrane thickness variations, rather than for instance in-plane geometric process variations. View full abstract»

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  • High-Capacitance-Ratio Warped-Beam Capacitive MEMS Switch Designs

    Page(s): 538 - 547
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    This paper presents a detailed analysis of the design, fabrication, and testing of a high-isolation electrostatically actuated capacitive shunt switch for X-band applications. The dual-warped-beam switch's RF performance is fine-tuned simultaneously in the off and on states by introducing warped bimetallic beams to the switch's edge to increase the effective capacitive area in the downstate and to the switch's center to decrease the effective capacitive area in the upstate. As a result, the dual-warped-beam switches demonstrate an off-to-on capacitive ratio of up to 170 without the need for thin dielectrics or high dielectric constant materials, exhibiting excellent RF performance. High isolation at X-band of less than 40 dB is also obtained with the introduction of inductive meandered springs into the switch structure. This novel tuning design mechanism for capacitive switches utilizing warped bimetallic beams has the advantage of simplicity and flexibility without the added complexity of using thinner dielectrics, tuned circuits, or larger size. View full abstract»

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  • Wafer-Level Transfer Technologies for PZT-Based RF MEMS Switches

    Page(s): 548 - 560
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    We report on wafer-level transfer technologies to integrate PZT-based radio frequency (RF) microelectromechanical-systems switches on CMOS. Such heterogeneous integration can overcome the incompatibility of PZT material with back-end-of-the-line (BEOL) CMOS technology. The PZT stack and the transfer process have been optimized to avoid degradation of the PZT actuators during the transfer. In particular, we have optimized the seed layer for the growth of highly oriented PZT on a patterned TiO2-Pt layer, optimized the electrodes structure, and developed an Al2O3 capping layer to prevent degradation of PZT during the transfer process. A full wafer-level transfer process and a selective transfer technology allowing the distribution of RF switches from one source wafer to many receiving wafers has been demonstrated. The latest transfer process demonstrated exhibits great potential for cost optimization of wafer-level transfer of microdevices. In a separate experiment, we have demonstrated the BEOL CMOS compatibility of our integration technique. Switch characterization showed insertion loss of less than 0.5 dB and an isolation better than 30 dB for the 0.4- to 6-GHz frequency range with 15-V actuation voltage. View full abstract»

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  • Development of a High-Performance Microelectrostatic Repulsive-Force Rotation Actuator

    Page(s): 561 - 569
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (749 KB) |  | HTML iconHTML  

    A high-performance microelectrostatic repulsive-force rotation actuator is developed and tested. A model of the actuator is also developed and used for design optimization. The model is developed using a hybrid approach that combines analytical analysis with numerical simulations. Expressions and a systematic method are developed based on this model for selecting the parameters of the actuator in order to achieve the maximum stroke for given operating conditions and geometrical parameters. An expression for the finger width leading to generating a maximum torque within the actuator was derived. A method was then developed to optimize the finger length and finger width of the actuator to achieve the maximum stroke. The design-optimization process proposed was used to design a repulsive-force rotation actuator which was fabricated using a standard multiuser surface micromachining process. The performance of the optimized actuator showed an improvement of more than 100% in comparison with a nonoptimized design which was fabricated using the same process and which had the same size, the same suspension spring stiffness, and was subject to the same driving voltage. The optimized actuator can rotate a 312 ??m ?? 312 ??m micromirror out of plane by 4.4?? at a driving voltage of 200 V, while the nonoptimized actuator could only rotate a micromirror of the same size by 2.1??. View full abstract»

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  • Multifrequency Pierce Oscillators Based on Piezoelectric AlN Contour-Mode MEMS Technology

    Page(s): 570 - 580
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    This paper reports on the first demonstration of multifrequency (176-, 222-, 307-, and 482-MHz) oscillators based on the piezoelectric AlN contour-mode microelectromechanical systems technology. All the oscillators show phase noise values between -88 and -68 dBc/Hz at 1-kHz offset frequency from the carriers and phase noise floor values as low as -160 dBc/Hz at 1 MHz offset. The same Pierce circuit design is employed to sustain oscillations at the four different frequencies; on the other hand, the oscillator core consumes 10 mW. The AlN resonators are currently wire bonded to the integrated circuit realized in the AMIS 0.5-??m 5-V complimentary metal-oxide-semiconductor process. Limits on phase noise and power consumption are discussed and compared with other competing technologies. This paper constitutes a substantial step forward toward the demonstration of a single-chip multifrequency reconfigurable timing solution that can be used in wireless communications and sensing applications. View full abstract»

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  • Fabrication and Characterization of the Capillary Performance of Superhydrophilic Cu Micropost Arrays

    Page(s): 581 - 588
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    We report the fabrication of dense arrays of super-hydrophilic Cu microposts at solid fractions as high as 58% and aspect ratios as high as four using electrochemical deposition and chemical oxidation techniques. Oxygen surface plasma treatments of photoresist molds and a precise control of the initial electrodeposition current are found to be critical in creating arrays of nearly defect-free Cu posts. The capillary performance of the micropost arrays is characterized using capillary rate of rise experiments and numerical simulations that account for the finite curvatures of liquid menisci. For the given wick morphology, the capillary performance generally decreases with increasing solid fraction and is enhanced by almost an order of magnitude when thin nanostructured copper oxide layers are formed on the post surface. The present work provides a useful starting point to achieve optimal balance between the capillary performance and the effective thermal conductivity of advanced wicks for micro heat pipes. View full abstract»

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  • Design and Fabrication of DRIE-Patterned Complex Needlelike Silicon Structures

    Page(s): 589 - 598
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    This paper reports the design and fabrication of high-aspect-ratio needlelike silicon structures that can have complex geometry. The structures are hundreds of micrometers tall with submicrometer-sharp protrusions, and they are fabricated using a series of passivated and unpassivated deep reactive-ion etching (DRIE) steps. A simple model is presented to predict the geometry of the structure based on the etch mask and the etch sequence. Model predictions are in good qualitative agreement with fabrication results, making it a useful design tool. The model is compared with literature reports on tapered DRIE. View full abstract»

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  • Magnetic Self-Assembly of Millimeter-Scale Components With Angular Orientation

    Page(s): 599 - 609
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    The focus of this paper is the demonstration and evaluation of a multifunctional self-assembly process driven by the intermagnetic forces between permanent (hard) magnets on 1 mm ?? 1 mm ?? 0.5 mm Si parts. Composite bonded-powder micromagnets are embedded in silicon components using back-end low-temperature wafer-level microfabrication techniques. Part-to-part assembly is demonstrated by batch assembly of free-floating parts in a liquid environment with the assembly yield of different magnetic patterns varying from 88% to 90% in 20 s. Part-to-substrate assembly is demonstrated by assembling an ordered array onto a fixed substrate in a dry environment with assembly yield up to 99% in just 20 s. In both cases, diverse magnetic shapes/patterns are used to control the alignment and angular orientation of the components. Experimental analysis of many different magnetic patterns shows that patterns with more planes of rotational symmetry result in faster assembly speeds. View full abstract»

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  • Multifunctional Tunable Optical Filter Using MEMS Spatial Light Modulator

    Page(s): 610 - 618
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    In this paper, we introduce a multifunctional tunable microelectromechanical systems (MEMS) optical bandpass filter that can continuously and independently tune the center wavelength and the passband spectral width. The filter function is achieved by dispersing the input light on a MEMS spatial light modulator (SLM) that is implemented with gold-coated mirrors microassembled on a MEMS platform. The mirrors are actuated by electrostatic combdrives that are bidirectional and have a maximum stable displacement of 44 ??m in both directions for a total range of 88 ??m. By actuating the SLM, the 1-dB bandwidth of the filter can be continuously tuned from 0.1 to 1.3 nm, and the 3-dB bandwidth can be tuned from 0.3 to 1.5 nm. In addition, the center wavelength can be fine tuned by actuating the movable blocking mirrors and coarsely tuned over a large spectral range by rotating the grating. View full abstract»

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  • Design, Fabrication, and Characteristics of a MEMS Micromirror With Sidewall Electrodes

    Page(s): 619 - 631
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2027 KB) |  | HTML iconHTML  

    This paper presents a 2-DOF silicon-on-insulator (SOI) microelectromechanical systems (MEMS) mirror with sidewall (SW) electrodes. The biaxial MEMS mirror with SW is actuated by electrostatic actuators. The dimension of mirror plate is 1000??m ?? 1000??m, with a thickness of 35 ??m. The analytical modeling, fabrication process, and performance characteristics are described. This paper analyzes the effects of the three-end single crystal serpentine torsion bar width and the bottom and SW electrodes on the performance of the mirror. A new fabrication process based on SOI wafer, hybrid bulk/surface micromachined technology, and a high-aspect-ratio shadow mask is presented. In comparison to previous fabrication processes and the Optical iMEMS process, the process is novel, easily understood, and simple to realize. The measured maximum angular deflection achieved is ??11??(mechanical angle) at a static operating voltage and is ?? 21??(mechanical angle) at resonance frequency driving. This mirror is well suited for applications where these characteristics are critical, such as in confocal or endoscopic scanning elements View full abstract»

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  • Rotating Out-of-Plane Micromirror

    Page(s): 632 - 639
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    Out-of-plane micromirrors have been developed for a wide range of applications including optical switching, beam steering, and precise transmission and reception of bio-optical signals. This paper focuses on the design, simulation, and testing of a rotating out-of-plane micromirror. The system consists of a polysilicon micromirror, which is erected to an out-of-plane position using a relatively simple postprocessing procedure. The mirror is mounted on a gear which has a rotational freedom of 360?? and can be driven at frequencies ranging from 1 to 1000 Hz using an electrostatically actuated rotational drive. Multiple out-of-plane configurations of the mirror are possible, with each utilizing a serpentine spring that attaches the mirror to the gear and a position specific ??catch block?? to allow 30 ??, 45?? , 60??, 75??, and 90?? orientations of the mirror. This paper focuses on the 45?? out-of-plane mirror, and it was tested for robustness as well as optical performance. A good correlation was found between experiment and various simulations. View full abstract»

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  • Investigation of Optical Power Tolerance for MEMS Mirrors

    Page(s): 640 - 646
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (630 KB) |  | HTML iconHTML  

    Optical power tolerance on micromirrors is a critical aspect of many high-power optical systems. Absorptive heating can negatively impact the performance of an optical system by altering the micromirror's curvature during operation. This can lead to shifts in the beam waist locations or imaging planes within a system. This paper describes a scheme to measure the impact of mirror heating by optical power and determine the power tolerances of micromirrors with gold and aluminum coatings using a 532-nm laser. Results are compared with an analytical model of thermally induced stress and optical absorptive heating. Experimental data shows that gold-coated mirrors are able to handle 40 mW of optical power with a beam waist displacement of less than 20% of the output Rayleigh length, while aluminum-coated mirrors can tolerate 125 mW. Measured data along with modeling suggest that, with proper metal coating, optical powers greater than 1 W should not adversely affect the system performance. View full abstract»

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  • Nonlinear Dynamics of MEMS Arches Under Harmonic Electrostatic Actuation

    Page(s): 647 - 656
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1455 KB) |  | HTML iconHTML  

    We present an investigation of the nonlinear dynamics of clamped-clamped micromachined arches when actuated by a dc electrostatic load superimposed on an ac harmonic load. The Galerkin method is used to discretize the distributed-parameter model of a shallow arch to obtain a reduced-order model. The static response of the arch due to a dc load actuation is simulated, and the results are validated by comparing them to experimental data. The dynamic response of the arch to a combined dc load and ac harmonic load is studied when excited near its fundamental natural frequency, twice its fundamental natural frequency, and near other higher harmonic modes. The results show a variety of interesting nonlinear phenomena, such as hysteresis, softening behavior, dynamic snap-through, and dynamic pull-in. The results are also shown demonstrating the potential to use microelectromechanical systems (MEMS) arches as bandpass filters and low-powered switches. An experimental work is conducted to test arches realized of curved polysilicon microbeams when excited by dc and ac loads. Experimental data are shown for the softening behavior and the dynamic pull-in of the curved microbeams. View full abstract»

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  • Nanomechanical Proximity Perturbation for Switching in Silicon-Based Directional Couplers for High-Density Photonic Integrated Circuits

    Page(s): 657 - 662
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (570 KB) |  | HTML iconHTML  

    We describe and demonstrate nanomechanical near-field proximity perturbation for tuning the effective refractive index of silicon-based high-density photonic integrated circuits. The proximity perturbation technique causes an antisymmetric refractive index change in a directional-coupler implementation, enabling switching action from the cross to the bar state. An almost 8-dB extinction ratio with ~14 ?? ??s switching speeds is experimentally achieved using this technique with our single-mode waveguides of 500 nm ?? 200 nm cross section coupled to a movable 100-nm perturbing dielectric. A practical single-level switch with ring resonators fabricated by CMOS-compatible methods is also demonstrated. 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